Pin It


How to Insulate Windows of All Types and Repair Windows to Seal Air Leaks, and How to Cover Windows With Heat Control Window Film and Reflective Window Film.


Topics

How to Check Your Primary Windows for Air leaks
How to Check Your Storm Windows for Air Leaks
Energy Tips for Windows
Types of Exterior Caulk and How to Apply Caulking
Weatherize Old, Wooden Double Hung Windows with Sash Cords
Weatherize and Repair Modern Vinyl, Fiberglass, Wood, and Aluminum Double-Hung Windows
Weatherize and Repair Old, Wooden Hinged Windows
Weatherize Sliding Windows
Weatherize and Repair Casement Windows
Weatherize Fixed Windows
Temporary Ways to Weatherize Your Windows
Heat Control Window Film and Reflective Window Film
Solar Screens
 

You can make any window air-tight, and it is better to do it yourself because hiring someone may cost more than you would save in energy costs. Also, if you do it yourself you can re-do it when necessary. Windows that have storm windows should also be weatherized, especially if your climate is cold or windy.

Many of the places where air can leak in also allow rain to enter, possibly causing damage to the walls. I found this information from my experience in weatherizing and repairing windows as a handyman, and from seeing weatherization that was done on windows I was repairing, and from reading do-it-yourself websites.

How to Check Your Primary Windows for Air Leaks

Primary windows are any windows that are not storm windows. Air leaking in or out of the house is called “infiltration”. “Air leaks” and “infiltration” are used interchangeably in this web page. A sash is a panel that contains one pane of glass or many small panes of glass. Most windows are double hung windows, which have an upper and a lower sash. A fixed window has a single sash, which does not open. 

Before testing a window that has a storm window, open the storm window. Windows with storm windows should be checked for infiltration because the storm windows may be left open occasionally, especially in summer when infiltration will raise the air conditioning bills. Also, storm windows have two “weep holes” at the bottom to let rain water flow out, and there may be cracks in the caulking between the storm window frame and the walls of the house.


Seal the Visible Gaps before Testing for Air Leaks

    • Before testing the windows for air leaks, seal all of the visible cracks and gaps where air could enter the house. Inside the house, caulk any visible gaps between the wall and the window trim (casing), along the sides, top and bottom. Use siliconized acrylic latex caulk, for “indoor/outdoor use”. This is more durable than the main alternative, latex painter’s caulk. See the topic, Types of Exterior Caulk and How to Apply Caulking

    • Outside the house, caulk any visible gaps between the molding around the windows (brick mold) and the wall of the house, and between the window frame and the molding. If you have wooden molding covered by vinyl or aluminum sheet metal, apply a wide bead of caulk where the sheet metal meets the wall of the house and press it down firmly with your finger. The caulk seals the edge of the strip to the wall.

If you have vinyl (PVC) windows, use an exterior sealant that lists vinyl as a material it adheres to. Check around the outer edges of the vinyl window frame and where the trim contacts the wall. It is important to check along the bottom edge of the window frame because gaps here will allow rain to enter the walls most easily, but  gaps anywhere could also allow rain to enter. To caulk vinyl windows, see the section Insulate and Repair Vinyl Windows. To caulk outside the house, see the topic, Types of Exterior Caulk and How to Apply Caulking

Brick Molding Around Hinged Window

    • Before testing a double hung window for infiltration, close the thumb latch and check that this closes the gap between the sashes. If the thumb latch (or thumb latches) are missing or broken, replace it before testing the window. If a thumb latch does not close because its two parts will not line up because the lower sash is too high, remount the rear piece of the thumb latch to a slightly higher level by putting a piece of cardboard or shim under it. Replace its screws with longer screws or the thumb latch will not secure the window as well.

    • Before checking a window for air leaks, open it and inspect the insulation strips that are compressed against the frame (not those on the sides of double hung windows that the sashes slide against). There may be, for example, metal strips that are flattened out and you can bend back into place. There may be vinyl fins that are damaged and you can fix or replace.

    • If a wooden sash rattles when the wind blows, it is loose and air will leak through. Remove the window stops and nail them slightly closer to the sashes. Nail on each window stop with only two 1½” finish nails, and then check that the sash opens easily before nailing in more nails.


Test for Air Leaks

    • Whether you test in summer or winter, it is best to test on a windy day. If you are testing in winter, choose a very cold day to detect the smallest air leaks. If you are testing in summer, choose a very hot day. Take these to lower the air pressure in your home. You are testing for warm air entering the home and more will enter this way.

      1. Turn off all air conditioners immediately before testing. These blow air into the home, raising the air pressure.
      2. Turn on all kitchen and bathroom exhaust fans and vented kitchen range hoods.

    • If you are testing the basement windows in the summer, do not take steps to lower the air pressure. In the basement, cold air flows out of the house because the air pressure is high there when the air conditioning is running. It flows out most forcefully when the pressure in the house is highest.

    • There are several ways to check for air leaks. One good way to check in winter is to moisten your hand on a very cold day and feel for air. The most accurate way to find air leaks is by using an incense stick. This can be used in winter or in summer, when no other way is effective. If the flame doesn’t rise straight up air leaking in is pushing it to one side. Incense sticks are better than candles for this purpose because their smoke is colored, but candle smoke can be almost invisible. Incense sticks are sold at some large discount stores and at several types of specialty stores.

Spot Thermal Camera

    • Another way to check for air leaks is with a “spot thermal camera”. You can order this at some home centers for about $200 for their least expensive model and you can use it to check for leaks around the doors and other places where air could be entering. It shows heat patterns by measuring infrared radiation. In winter, it shows cold spots where cold air enters, and in summer it shows warm spots where warm air enters. This will save you much time if you are checking many windows and doors.

    • Using one of the methods above, check around the outer edges of the glass and the outer edges of the sashes and where the sashes meet. If there are visible gaps where the window trim (casing) meets the wall, check there also. Check from the inside of the house.

    • In the summer months, while a home is being cooled by central air conditioning, warmer outside air will enter through gaps around the windows. This is convection, in which warmer air flows to displace cooler air. At times, the air in the basement can be the coldest in the house, and the air pressure there is higher than outdoors. This is especially true in a three-story house with good air conditioning. Cold air falls downward, increasing the air pressure in the basement. When the air pressure there is high, air escapes through any gaps around basement windows and doors. To test for air leaks in the basement windows with a thermal camera, view the windows from the outside and from the inside because it is unknown which way leaking air is flowing.

    • In the winter months when the central heating is operating, the air pressure is always lowest in the basement and highest on the top floor.  This is because the central heating causes the air to expand, become lighter, and rise to the top of the house. This is called “the chimney effect”. The air escapes through the attic vents, and draws in an equal amount of cold, outside air through opened doors and leaks in the house. Since the air pressure is lowest in the basement, gaps around basement windows will allow air to be drawn in most forcefully, so these should be carefully found and fixed.

On the top floor, the air pressure in the heating season will be close to the outdoor air pressure. There could be gaps that you don’t detect because no air is leaking through them. Check them on a windy day using an incense stick. Wind draws air out of the house so the smoke will lean toward the window if there is a gap. If you have central air conditioning, you could check for infiltration on the top floor when it is turned on.

    • To determine if your upper floor windows have air leaks, tape a 1 mil thick plastic drop cloth over some of these windows on a windy day. If there is infiltration the drop cloths will billow.

    • If you live in a climate where you use no central heating and you use fans and window A/C units in place of central air conditioning in summer, there are ways to check for air leaks. You can check for air leaks on a very windy day at any season of the year using an incense stick to detect air motion. A strong wind draws air out of the house. On a day with mild wind, you could tape a 1 mil thick plastic drop cloth over the windows you are checking and watch them while the wind blows. If there is an air leak, the drop cloths will billow when the wind blows.

a
How to Check Your Storm Windows for Air Leaks

    • At each window that has a storm window, open the primary window and check the storm window for air leaks. If there are air leaks the storm window is probably not sealed tightly against the window frame. Either the screws that mount it have come loose or the caulking around the edges of the storm window has failed, or caulking was never applied. There should be two holes in the metal frame of the storm window where it contacts the window sill. These allow rain to escape if the storm window is open during a rain. Check that these holes are open and not clogged with dirt.

a
Energy Tips for Windows

How do you insulate windows instead of replacing them with double pane windows? There are many small things you can do.

    • If you have windows of any type, sliding, hinged, etc., that you never open, caulk around their sashes with clear interior/exterior caulk to seal the gaps. If you have double hung windows with upper sashes that you never open, these will probably be painted shut and the gaps around the sashes will be sealed by paint. Check if there are visible gaps around those that don’t slide down and caulk to seal the gaps. If there are upper sashes that slide down which you never open, caulk those also with interior/exterior caulk.
    • Do not seal the gaps around the window of your furnace room if you have an old furnace that does not have air supplied to it from outside through a pipe, unless the furnace room has a louvered door. A louvered door has slots to allow air to flow through. The air supply pipe is a large plastic pipe. These have been required for many years. In some old homes, the door is not louvered and a drafty furnace room window provides much of the oxygen used by the furnace flame.

A gas furnace that operates with very poor combustion due to a serious lack of oxygen could produce a dangerously high level of carbon monoxide. If you weatherize a drafty window in your furnace room and you are afraid that the furnace may not receive enough oxygen, there are two ways to increase the oxygen: 1) replace the furnace room door with a louvered door, or 2) cut off 1” or more from the bottom of the door. Also, mount a carbon monoxide monitor on the basement wall near the floor. All homes with gas furnaces or gas ovens should have one. They sound an alarm when poor combustion causes a high level of carbon monoxide.

    • If you live in a hot, sunny region and your air conditioning costs are very high, consider replacing your screens with solar screens. See the section Solar Screens
    • Check that all double hung windows have working thumb latches. Thumb latches are designed to pull the two sashes together to close the gap between them, which would allow air to leak through. On some windows, closing the thumb latch prevents the upper sash from falling slightly, leaving a small gap at the top. This happens when the springs in the spring balances lose tension from being stretched.

If a thumb latch will not close, it is either because the upper sash doesn’t reach the top or the lower sash doesn’t set low enough. Clean out the channels and scrape the paint from surfaces of the sashes at the top and bottom of the window. If it still will not close, remount the rear piece of the thumb latch at a slightly higher level by putting a shim or two or three pieces of cardboard under it. To make a shim, use a knife to cut a piece the size of the latch from an 8” wooden shim. The screws will be too short, so replace them with longer screws, such as 1¼” drywall screws.

Glazier’s Points
    • If there is infiltration between the glass and the window frame in a window with glazing putty, replace the glazing putty because it has dried out. Check the other windows because they were probably glazed at that time. If glazing putty is many decades old, it contracts and water enters the crack and freezes and breaks out the putty. Air can leak through and water can damage the wood. If there is infiltration because the pane is slightly too small, do not seal the leak with thicker glazing putty. The pane would knock it out because it has no glazier’s points on that edge. Replace the pane with a larger pane. To replace the putty:
        1. Chisel out the putty with a sharp wood chisel
        2. Prime the areas where the wood is bare using an oil-based primer. Paint at least two days after a rain and allow the paint to dry before applying the putty.
        3. If the putty has fallen out on one edge of the pane, the pane may have been mounted without enough glaziers’ points, allowing it to vibrate and break out the putty. There should be at least two glaziers’ points on each edge of the pane. If there aren’t, put in more. Push them in with a chisel or putty knife, being careful not to crack the glass.
    • On wooden and metal windows with glazing putty, paint the putty to extend its life. Glazing putty should be painted when applied, but rarely is because the glazier must return days later to do this. The paint traps the linseed oil, and unpainted, the oil very slowly evaporates until the putty shrinks and falls out. Painting it also seals the gap between the putty and the glass, preventing water from entering. If the window is double glazed, i.e., it has two panes with an air gap between, painting the putty will help prevent water vapor from entering the air gap and fogging up the window.

To seal the gap, apply the paint slightly onto the glass, covering the crack. Use high quality oil-base paint. Paint on a warm, sunny day so the glass will be dry, and do not paint before 10 AM because the surfaces may be damp from dew.

    • Thumb latches on double hung windows pull the sashes together to close the gap and prevent infiltration. Some people don’t close the second floor thumb latches because they believe their only purpose is to lock the windows. If your thumb latches are often left open, stick small self-sticking labels next to them, with PLEASE CLOSE THIS LATCH.

    • Make improvements to lower your home’s humidity if you have drafty windows and you don’t weatherize them because your home would become too humid, or if you leave some windows partially open on very cold days to prevent them from fogging up. These are ways to lower your home’s humidity:
      1. If you have a crawl space with a bare ground floor, cover it with 6-mil thick polyurethane sheeting. This is sold in the paint departments of home centers and in paint stores.
      2. Hire a contractor to install bathroom exhaust fans in the bathrooms where the showers or bathtubs are used every day, and/or a range hood that vents outdoors if you cook food often in boiling water. The cost of installing and operating either of these would probably be greater than the money you save by insulating your windows, but these improvements have other advantages. Installing bathroom exhaust fans will prevent your bathroom mirrors from fogging up, reduces mold from forming on the bathroom ceiling, and increases the property value of the home. A range hood will remove much of the smoke when frying food to keep the kitchen clean, and increase the property value of your home.
    • If you have single pane windows and will not install storm windows, replace the sashes with double pane sashes. These will greatly reduce the R-value of the panes and you can install low-E glass for even greater insulation. See the section, Heat Control Window Film and Reflective Window FilmThere are two ways to replace your sashes with double pane sashes:
      1. Mount double glazed panes in the existing sashes. You can only do this if you have wooden sashes. These may be called “thermopane” windows. A millwork shop should do this unless you have a wood shop and the necessary power tools.  The least expensive double glazed panes are not recommended because they may fog up in 10 to 20 years and cannot be repaired, but if your climate is dry they will last much longer.
      2. Install “double pane replacement sash kits”. These can be installed by do-it-yourselfers. A kit includes an upper and lower sash and window jambs with spring balances. The sashes and window jambs are mounted into the opening that held the old sashes so the windows are smaller in height and width.
Double Pane Replacement Sash Kit
    • If your windows have factory-installed pile, vinyl bulb or vinyl strip weatherstrip, check if it is damaged or missing. Pile weatherstrip is in thin, brush-like strips. Replace any worn-out weatherstrip. Home centers carry a small selection of these, window repair stores have a greater selection, and retail stores that carry that brand of window should have the weatherstrip available. Weatherstrip for windows is often unique to that brand and must be ordered from the manufacturer.
    • If the original windows had counter balance weights (window weights) and were replaced by windows using spring balances, fill the chambers that contain the counter balance weights with insulation. The chambers are large, hollow boxes. The air in them is cold in winter and it leaks into the house through large gaps at the window pulleys. Use “minimal expanding” spray foam insulation, also called “spray foam for doors and windows”. Other types of spray foam insulation could cause the jamb to bend. Shoot it in through the openings at the window pulleys. The disadvantage is that each window will require two cans, which, for the entire house is expensive and only a good investment if your climate is very cold.
    • If a lower sash with spring balances rises slightly when you release the thumb latch, the springs are too tight. It should be repaired because residents may occasionally close the window without latching the thumb latch, allowing the sash to rise. To repair it, disconnect the balance on one end, rotate it a few  turns and reconnect it.
    • If your basement is well lit with electric lighting, you could cover the basement windows with heavy plastic sheeting for inexpensive, long-lasting insulation. Heavy sheeting is translucent (lets light through), but is not transparent. This should be more durable than the transparent “shrink film” but doesn’t let in as much light. Staple it on, then nail on a frame of thin wooden strips such as furring strips to make it air-tight and permanent. For better insulation use several layers with air gaps between. Plastic sheeting is sold in paint departments and paint stores, for use as a drop cloth.
Portable air purifier
    • If you leave a window partially open in winter because a smoker uses the room, buy an air purifier for that room so the window can be closed. Air purifiers have a fan that blows the air through a filter. Models  suitable for smokers are portable and are sold in many types of stores for $150 to $200. Their labels or websites indicate that they “remove odors and particulars”. Air purifiers with HEPA filters may be unnecessarily expensive. They are designed to remove allergens. Most if not all portable air purifiers have three or more speeds, so if the highest speed trips the circuit breaker a lower speed can be used.
    • If you have a broken double glazed window pane you can replace it yourself. Remove the sash and take it apart by removing the screws. Use a utility knife to cut the rubber to remove the pane. Buy a pane of this size from a hardware store and reassemble the sash.
    • If there is a transom above your front door, check the transom for infiltration. These homes are very old, so air often leaks in from around the pane because the glazing putty has fallen out. Seal leaks around the pane by re-glazing the window. The instructions for glazing are given on a can of glazing putty. If the putty is hard to remove, use a sharp wood chisel. Re-glazing the transom also prevents moisture from destroying the wood. Allow the putty to dry for the period of time given on the can, and then paint it. Paint to very slightly cover the glass to seal the crack between the putty and the glass. This will prevent water from entering, freezing and breaking out the putty.
    • If you have a stained glass window with infiltration around the edges of the glass, seal the gaps with clear silicone caulk designed for windows and doors.
Cupola
    • If your home was built in the nineteenth or early twentieth century, there may be a window on the ceiling of the top floor that opens to allow air to flow up to a cupola on the roof. Cupolas have vanes that are tilted to prevent rain from entering, but air passes through them freely. The window is a sash which opens by pivoting at its center when a chain is pulled downward.
Vinyl bulb weatherstrip

When the window is closed, the sash does not rest against a window stop, so there will by a narrow gap around it, unless it is sealed with weatherstrip. If there is a gap, wind blowing over the cupola draws air forcefully up through it, so it should be sealed. If the window is never opened, caulk the gap.

If the window is opened, mount vinyl bulb weatherstrip (tubular vinyl weatherstrip) to the upper surface of the sash, along the edges that move up when the window is opened. Where the edges of the sash move downward, mount weatherstrip to the window jamb.  Vinyl bulb weatherstrip should be used because it is more durable than felt or foam rubber weatherstrip. It is not self adhesive, so it must be nailed on. Use brass weatherization nails, sold in the weatherization section of home centers and hardware stores.

nnnnnnnnnnnnnnnnnnnnnnnnnnn
Types of Exterior Caulk and How to Apply Caulking
nnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn
How to Apply Caulking at Windows

  1. If you are replacing old caulking, use a very sharp wood chisel or stiff putty knife and thoroughly scrape it out. Some types of caulk do not stick to some others.  Also, the old caulking may be too dusty for the other to stick to it, and the old caulking may come loose if it is very old. If you fill a crack in old caulking, the new caulk can’t expand enough when the surfaces move relative to each other, so it may become loose. aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
  2. Cut off the tip of the tube of caulk with a knife. Don’t use the cutter in the handle of a caulking gun; these don’t cut well. To fill a gap outside the house, where appearance is less important than inside, push the caulking gun forward as you release the caulk to force the caulk into the gap. aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
  3. The variety of caulks available at home centers and paint stores can be overwhelming, but it can be simplified. Most exterior caulks are labeled as “sealants”. A sealant is a caulk that is formulated to be more elastic. Always use a sealant when you caulk outside the house because the gap may expand and contract with changing temperature. This is particularly important when sealing a gap between metal and wood or brick. Carefully read the label before buying a sealant. They differ in allowable weather conditions for application, materials they adhere to, and in other ways. aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
  4. Some sealants do not adhere well to vinyl. When caulking vinyl windows or siding (where window trim meets the siding), use a sealant that lists vinyl a material it adheres to. Most, if not all brands of polyurethane sealant list it, but this is hard to apply neatly because it can smear. Silicone sealants do not list it. There are brands of “window, door and siding sealant” that do list vinyl.

Types of Exterior Caulk

Siliconized Acrylic Latex Caulk, for “Indoor/Outdoor Use”

    • Ideal for weatherizing inside the home
    • May be called “silicone acrylic”
    • Less durable than most outdoor caulks and sealants, may be labeled “lasts 10-20 years”
    • Paintable, unlike most sealants
    • Available in many colors.
    • Adheres to many materials, brands differ

Silicone Sealant

    • Excellent durability, may be formulated to last 50 years
    • Excellent elasticity, may be labeled as expands 30%
    • Surfaces must be completely dry before caulking. Surfaces may be damp when you cannot see dampness, as in shady areas on cool days.
    • Not Paintable.
    • Most brands do not adhere to brick or concrete
    • Adheres to glass
    • Can be applied at very low temperatures
    • Can be used in very damp areas
    • Available in several colors
    • Most brands should not be used with vinyl because it damages vinyl while it cures.

Polyurethane Sealant

    • Most brands are hard for an inexperienced person to work with. They are sloppy and smear, giving poor appearance.
    • Excellent durability, but may deteriorate with long-term exposure to direct sunlight.
    • Very elastic
    • Many brands can be applied to a slightly damp surface.
    • Available in many colors.
    • Some brands adhere to wood, metal, stone, PVC, glass and masonry, but not all brands, so you must read the label.

All Weather Sealants

    • May be applied at very low temperatures
    • May be applied to wet surfaces

 

Weatherize Old, Wooden Double Hung Windows with Sash Cords 

 

Wooden Double Hung Window

Insulating old, drafty wooden double hung windows not only lowers your utility bills, but may prevent uncomfortable cold drafts, may make your home quieter, and may prevent water from entering the walls, doing damage to the home.

Seal the Gap between the Upper and Lower Sashes

    • If there is infiltration between the top rail of the lower sash and the bottom rail of the upper sash (between the “meeting rails”), first try to close this gap without mounting weatherstrip because weatherstrip may not be permanent and some types are unattractive. Double hung wooden windows were designed to have no gap between the sashes when the thumb latch is closed. The thumb latch pulls the bottom rail of the upper sash tightly against the top rail of the lower sash. If you can make these mating surfaces smooth, no air will leak through.
      1. The gap between these surfaces is most often caused by drops of paint, so first, try to remove any drops of paint by sliding a hacksaw blade through the gap.
      2. If the mating surfaces appear smooth but there is still infiltration and the window is very wide, replace the thumb latch with two thumb latches. This will pull the sashes together more tightly. Mount each thumb latch about ¼ of the way in from one end.
      3. If the gap still will not close, expose the two surfaces and scrape and sand them. They will be exposed if you lower the upper sash and raise the lower sash higher than the upper sash. If the upper sash will not slide down, paint is holding it. Cut through the paint with a utility knife, and use a pry bar or stiff putty knife to loosen it. Be careful not to make marks in the wood.
      4. If you cannot lower the upper sash because it has been painted shut from the outside and you don’t want to cut the paint from the outside, expose the two mating surfaces by removing the window stops and tilting the lower sash toward you. The sash cords will normally extend a few inches to allow the sash to tilt.
Lower sash raised above upper sash. View from outside the house.
    • To seal the gap by mounting weatherstrip between the sashes, nail a strip of spring bronze weatherstrip to the bottom rail of the upper sash.

Expose the mating surface of the upper sash, as explained above, either by removing the window stops and tilting the lower sash outward, or by raising the lower sash and lowering the upper sash until the lower sash is higher than the upper sash. If you remove the stops and tilt the sash forward you can close gaps between the window stops and the lower sash. Sand the surface of each window stop that contacts the sash and the surfaces they slide against on the sash. Wax them with paraffin wax or a candle and nail them on slightly closer to the sash than they were to lightly contact the sash. To remove and replace the window stops and mount spring bronze weatherstrip to the sash, see below, How to Remove and Replace Window Stops and Mount Spring Bronze.  bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

    • If you cannot expose the rail to mount spring bronze weatherstrip to it, you could mount vinyl bulb weatherstrip to the top of the lower sash. This will seal the gap well but it looks a little unattractive. Nail it on with copper weatherization nails. These are ¾” long and designed to attach weatherstrip. They are sold where weatherstrip is sold. Push them in using a brad driver or nail them in, holding them with needle nose pliers. It may be better to use a brad driver because using a hammer could knock loose pieces of glazing putty.

How To Remove and Replace Window Stops and Mount Spring Bronze

Tools and Materials:

    • 1½” finish nails
    • Painters putty
    • Caulk that matches color of window frame
    • Spring bronze weatherstrip, weatherizing nails should be packaged with it
    • Brad driver
    • Utility knife
    • Flexible putty knife to apply painter’s putty
    • Stiff putty knife or paint scraper to pry off window stops

Procedure:

      1. Use a utility knife to cut the paint where the window stops meet the frame
      2. Use a stiff putty knife or paint scraper to pry off the window stops. Be careful not to knick the wood
      3. Move the lower sash away from the upper sash enough to mount weatherstrip to the upper sash. The sash cords will normally extend out at least a few inches, so you won’t need to disconnect them to do the work
      4. Using shears or sharp scissors, cut a piece of weatherstrip
      5. Nail it to the bottom rail of the upper sash using the copper nails in the package, with its bottom edge slightly below the bottom edge of the sash. This will prevent the lower sash from catching on its lower edge when the lower sash is raised. To keep it perfectly straight and avoid bends, put in a nail on one end, pull it tight and put in a nail on the other end. Then put in nails at all of the nail holes
      6. Check that the weatherstrip has been mounted with no bends. If it has a bend, replace it
      7. Carefully bend the weatherstrip away from the sash, without causing permanent waves in it. It is initially flat but must be bent out to contact the sash
      8. Clip off or hack off the nails from the window stops. Don’t push them back through and reuse them because this could damage the wood
      9. Nail on the stops with 1 ½ “ finish nails. Use nail set to drive them below the surface and cover them over with painter’s putty
      10. Caulk where the window stops meet the window frame

Seal the Gap Under the Lower Sash

Palm sander
    • If there is infiltration below the bottom of the lower sash (or above the upper sash if you open it) and the window is very old, try to repair the bottom surface instead of mounting weatherstrip. Make both surfaces smooth to create a tight seal. Sand the bottom surface of the sash with a palm sander using coarse sandpaper if it is not smooth, or use a belt sander if necessary. Be careful not to sand the edges and round them off. Scrape the paint from the window sill where the sash rests on it. On an old house there may be large drops of paint, or dried puddles of paint in the corners.
    • If you still have infiltration after repairing the window, there are several types of weatherstrip you could mount to the bottom surface of the sash. If you use self adhesive weatherstrip, nail it down because lifting the sash would otherwise break it loose. The weatherstrip must be very thin or the thumb latch will not close.

Types of Weatherstrip to Mount to the Bottom Surface of Lower Sash:

Spring Bronze Weatherstrip
      • Spring bronze weatherstrip. This is very thin when compressed. It is not perfectly air-tight but it should last for many years.
      • 3/16” thick foam self adhesive weatherstrip. This may have different names, such as “weather seal self-stick tape”. It is paper-thin when compressed, so it is ideal if the sash contacts the window sill on one side only. It is not durable.

Mount Spring Bronze:

    1. Check that the bottom surface of the sash and the sill below it are smooth and flat
    2. Cut a piece of the spring bronze using shears or sharp scissors
    3. Nail it on using weatherization nails, which should be in the package. Use either a hammer with needle nose pliers to hold the nails, or use a brad driver. Space the nails closely and nail in every other nail at a slight angle for greater strength. This is “toe nailing”. Without toe nailing them in they may not be strong because the wood may be slightly rotted
    4. Bend the strip out a little. Bend it carefully to not cause “waves” in it
    5. Close the window and check that the thumb latch still closes
    6. If the thumb latch doesn’t close, remount the part in the rear (the keeper). Remove it, put two pieces of cardboard under it as shims and screw it back down. Cut the cardboard around the thumb latch using a utility knife

 

Thumb Latch with Shim                      Copper Weatherization Nail           Brad Driver

Insulate the Sides of the Sashes

There are many ways to seal the gaps along the sides of a sash, depending on your ability as a do-it-yourselfer, the condition of the window, and other factors.

    1. Mount tubular vinyl gasket weatherstrip to the window frame. This looks a little unattractive and the weatherstrip will wear out from the sash rubbing against it. It may be suitable on windows that aren’t opened often.
    2. Insert spring bronze weatherstrip betwe en the sash and the window frame on each side. On many sashes there is not enough space for them, and they normally make the window harder to open.
    3. Remove the sash, cut grooves in it and mount pile weatherstrip into the grooves.
    4. Remove the window stops and remount them slightly closer to the sash. Smooth them and wax them so the sash opens fairly easily. This will block most of the infiltration. While they are removed you could mount spring bronze weatherstrip to the bottom rail of the upper sash.
    5. Install a “side window lock” on each side of the sash. These can be closed to push the sides of a sash against the window stop on the opposite side (the bead) to tightly close the gap.

These ways are explained below.

Heavy Duty Staple Gun

A. Mount tubular vinyl gasket weatherstrip to the window frame

Staple the weatherstrip to the window frame using a heavy duty staple gun and 3/8” staples, or nail it on with brass weatherization nails using a brad driver. Mounted with staples, it would not look as good but would be more durable. Mount it to very lightly contact the sash, because if the bulb is compressed by the sash, the weatherstrip will wear out much sooner.

Use sandpaper to smooth the surface of the sash that the weatherstrip will slide against. The weatherstrip will last much longer if it slides against a smooth surface and will make a tighter seal.

B. Insert spring bronze weatherstrip between the sash and the window frame on each side.

Typical spring bronze weatherstrip

Spring bronze weatherstrip is mounted by nailing on one edge and bending the weatherstrip away from the wooden surface. It is common on doorways of older homes. It has major advantages and disadvantages over the other good types of weatherstripping

    • Durable
    • Not air-tight
    • Often causes the sash to be harder to open
    • Often causes the sash to be harder to open
    • Can be mounted without removing the sash

Tools and Materials:

    • Package of spring bronze weatherstrip with brass weatherization nails in package
    • Metal shears or sharp scissors
    • Tape measure
    • Sharp 1/2″ or 3/4″ wood chisel
    • Brad driver, or needle nose pliers and hammer

Procedure:

    1. Using a wood chisel or sandpaper, smooth the surface of the window jambs where the weatherstrip will be mounted
    2. Use metal shears or sharp scissors to cut one piece of weatherstrip an inch longer than the height of the sash. Only one weatherstrip should be mounted, then test if the window has become harder to open. If so, you may not mount one on the other side.
    3. Raise the sash to the top and slip the weatherstrip in between the sash and the window jamb, being careful not to bend it.
    4. Locate the piece of wood that is the access panel for the window weight. This should be about 8” or 10” high, and is held in with one large screw at the top. Do not put any wire nails into it, unless they can be pushed in easily with a brad pusher. The access panel will break at the top if hammered into.
    5. Using a brad driver, or a hammer with needle nose pliers to hold the nails, nail the piece at the top and bottom, pulled tightly to avoid waves. If the access panel reaches the bottom of the channel, put one or two nails into it at the very bottom. It is stronger there than at its top.
    6. Put a nail in at each nail hole in the weatherstrip. If any of the nails go in more easily than the others, the wood is slightly rotten. This can be noticed more easily if you use a brad driver than if you hammer in the nails. If the wood is slightly rotten the nails may not hold. If the wood is soft, put in extra nails with every other nail driven in at a small angle. This is “tow nailing”; finish nails are often nailed in this way for greater strengthLower the sash and put nails in at the top.
    7. Bend the weatherstrip outward a little all along its edge. Be careful not to make bends in it, making it “wavy”; the bends will not straighten
    8. Check if the window is hard to open. If it is hard to open, do not mount a weatherstrip on the other sideIf the window is not hard to open, mount a weatherstrip on the other side.
    9. To make the window easier to open, rub a block of paraffin wax along all of the running surfaces, including the stops.

C. Remove the sash, cut grooves in it and mount pile weatherstrip into the grooves.

5/16″ Thick Pyle Weatherstrip

Pile weatherstrip, also called “brush weatherstrip” or “wool pile” may be the best weatherization material for wooden double hung windows, but it is the hardest to mount. It is very durable and doesn’t make the windows harder to open. To mount it you must remove the sash and cut channels for it. This is a do-it-yourself project, but you must have use of a plunge router or a table saw to cut the channels. Plunge routers are better for this and are not expensive.

Plunge router

Pile weatherstrip sold at home centers and hardware stores should not be used because it is only 3/16” thick (the pile plus the backing). It is sized for storm doors. Thicker pile is available at window repair stores and from online suppliers. Use pile weatherstrip with a base approximately ¼” wide and thickness of about 5/16” (.312”) or 350”. (The pile weatherstrip sold at hardware stores is much thinner).If the supplier does not tell you which adhesive to use or what the backing is made from, test several brands of epoxy by gluing a piece of the weatherstrip to wood. If it is made from vinyl, use an epoxy with vinyl listed as a recommended material. Not all epoxy’s can be used for vinyl. The least expensive plunge routers are good for cutting the channels for the weatherstrip. They are available for about $80 at home centers.

There are advantages and disadvantages to using pile weatherstrip:

    • Very durable
    • Air-tight
    • Does not make the sash harder to open
    • You must remove the sash to mount it
    • You must cut channels to mount it in
Brad driver

Tools and Materials:

    • Plunge router or table saw
    • Utility knife
    • Pry bar
    • Hammer
    • Metal shears or sharp scissors
    • Brad driver, or hammer and needle nose pliers to hold nails
    • Brass weatherization nails
    • Paint scraper
    • Sanding block
    • Paraffin wax
    • Epoxy for weatherstrip
    • 1 1/2″ finish nails
    • Nail set or square-cut nails
    • Painters putty
    • Putty knife
    • Interior caulking
    • Caulking gun
    • Touch-up paint
    • Paint brush
    • Mask designed for use with lead paint

Procedure: (lower sash only)

    1. If possible, work on a day that is not cold. The epoxy may have a requirement that the temperature be 50 degrees for many hours to dry
    2. Pry off the left or right window stop for the lower sash using a stiff putty knife or paint scraper. To prevent damaging the paint, first cut the paint with a utility knife where the window stop meets the jamb
    3. Saw off or clip off the nails sticking out from the window stop. Do not pull them out, this could damage the wood.
    4. Remove the sash. If it has sash cords with pulleys, remove the sash cords and tie them to objects that will stop them from falling into the chamber in the wall. If you don’t, the window weights will pull them into the chamber.
    5. Find a lead-safe work zone, such as outdoors or in a garage with open doors, to cut the channels. Old wooden windows often have lead paint as their lower coats of paint. Also, wear a mask.
    6. Cut channels for the weatherstrip. A router is the best tool for cutting the channels but a table saw could also be used. Cut them on the bottom and side surfaces. On the top rail, cut a channel on the surface that contacts the upper sash. Cut them 1/8” deep, and the width of the backing you bought. Backing is approximately 1/16” thick
    7. Glue in the pile with epoxy. You may need to leave the sashes inside all day as the epoxy dries if it is a cold day.
    8. Put in a brass weatherization nail or similar wire nail in each end of each piece of weatherstrip to hold down the ends. This will hold the ends in place while the epoxy dries and also add bonding strength.

D. Remove the window stops and remount them slightly closer to the sash.

If a sash can rattle forward and backward, there are gaps between the window stops and the sash that allow infiltration. Remount the window stops closer to the sash to seal the gaps.

Tools and Materials:

    • Sandpaper
    • 1 ½” finishing nails
    • Painter’s putty
    • Interior caulk
    • Sandpaper
    • Nail set or hard cut nail (square nail

Procedure:

    1. Cut the paint where the window stops meet the window frame.
    2. Use a paint scraper or stiff putty knife to pry off the window stops. Be careful not to damage the wood.
    3. Clip off the nails with a wire cutter or cut them with a hack saw.
    4. Scrape or sand the surface of the window stops that the sash slides against, down to the bare wood. It does not need to be repainted. Sand outdoors or wear a dust mask because it may be lead paint.
    5. Apply wax heavily to the bare wood surface to help the window open more easily. Use a candle or paraffin wax sold in bars.
    6. Sand the sash where it slides against the window stop and apply wax. Nail on the window stop to close the gap, use four 1 ½” finishing nails. Use a nail set or hard cut nail to drive the nail below the surface and fill the holes with painter’s putty.
    7. Caulk the crack between the window stop and the window frame.
    8. Check for paint drops on the small stop that separates the sashes (the bead) and remove them.
    9. Paint the window stops after the caulk has dried.
Side window lock

E. Install a “side window lock” on each side of the sash.

A side window lock or “window cam lock” pushes the sash against the window stop behind it. One can be mounted to the window stop on each side of the window. When you close them, you push the sash tightly against the stops behind the sash, which are the “beads” or “parting stops”. This closes the gaps. You will probably need to order them online.

Insulate or Repair Windows with Out-of-Square Frames

If your home is very old, some of the window sills may not be level because the home’s foundation has settled. These window frames will be out of square, causing a gap between the sash and the sill on one side of the sill and a similar gap at the top of the upper sash.

    • The most durable way to weatherize a window with an out-of-square frame is to cut a beveled piece of wood, the length of the window sill, to fill the gap. For example, if your window is 28” wide and 1 1/2 “thick, cut the piece 28” long and 1 1/2 “thick. Cut it as a wedge, with one end the thickness of the gap the other end paper-thin. A table saw should be used. Sand the bottom surface of the sash with a palm sander to remove all of the paint and glue the shim to it with polyurethane construction adhesive. This is better than nails because nails expand and contract as the outdoor temperature changes.
Beveled Piece of Wood Glued to Bottom of Sash
    • Instead of repairing it, you could use ¼ “x 1 ½ “ foam weatherstrip. This is not durable. Mount it in two layers where the gap is wide and one layer where the gap is narrow. It is self-adhesive, but you should also staple it using a heavy duty stapler.
    • If the upper sashes are painted shut and you use air conditioning, try to free up some of them to cool the home a little through convection. This should probably only be done if you have storm windows on those windows because freed up upper sashes might be a cause of infiltration. On evenings when it is cooler outside than inside, you can lower some upper sashes by a few inches and raise the lower sashes. Warm air from the top of the rooms will flow out and cooler outside air will flow in. This was commonly done before air conditioning was used. You can normally free up an upper wooden sash by cutting through the paint, and prying the sash free using two paint scrapers or stiff putty knifes. Sashes are rarely painted shut from outside of the house, but check for this first. If they are, you would need to free them from the outside of your house.
    • If a window with spring bronze weatherstrip mounted to the window jambs or to the top of the upper sash or the bottom of the lower sash is allowing infiltration, bend out the spring bronze. It may have flattened a little over time. If there is still an air leak, the spring bronze may have been mounted with a slight curvature and must be re-mounted. They are not original to old wooden windows, so they may have been mounted poorly.
    • If there is a small rotted area on the bottom surface of the lower sash which allows infiltration, fill it with epoxy wood filler. First, scrape away the wood that is soft because it contains rot, which will spread. Then, drill many small, short holes into the sash, for the epoxy wood filler to adhere better. Without these holes the wood filler would be knocked off more easily by closing the window. Apply a wood hardener to that surface, which is designed for this purpose. Wood hardener and epoxy wood filler are sold at hardware stores, paint stores and home centers.
    • If a sash is badly deteriorated, check if the bottom of the pane(s) contacts the bottom rail of the sash. The bottom rail may have deteriorated from rot, allowing a gap. If there is a large gap, apply wood hardener to prevent further rotting. Seal the gap with clear “silicone caulk for windows, doors and siding”. Silicone is one of the few caulks that adheres to glass. If the weather is cold or was cold earlier in the day, the sash and the glass will be slightly damp from condensation. If so, dry the area thoroughly with a hair dryer before applying silicone caulking.
Fasten upper sash into place with two screws
    • If an upper sash is working but you never open it, fasten it into place with two screws and caulk around its edges with clear indoor/outdoor caulk. Long trim screws are good for this because they have small heads that you barely see. Put in the screws through the bottom surface of the sash, at a 45 degree angle to go into the window frame.
    • If the bottom rail of either sash has separated slightly from the side rails, repair the sash. The pane may have fallen down onto the rail, leaving a gap above it. Force the bottom rail up, if possible and fasten it with two metal corner braces on the outer side of the window. If the pane cannot be forced back up, fasten it in the position it is in using corner braces to prevent it from falling further. If there is a gap above the pane that you can’t close, seal it with clear “silicone caulk for windows, doors and siding”. Silicone is one of the few caulks that adhere to glass. If the weather is cold or was cold earlier in the day, the glass will be slightly damp from condensation, so first dry it with a hair dryer.
Bottom of sash repaired with braces
    • If your home is very old, some of the window sills may have fallen slightly, causing a gap between the lower sash and the window sill. Old wooden window sills have two pieces; one inside the house and one outside the house. They overlap and the piece inside the house is above the outside piece. When the window is closed, the sash rests on the piece that is outside of the house. On very old homes, this piece may fall and become separated from the other piece, leaving a gap below the sash. To repair it, first apply construction adhesive between the two pieces. Lift the lower piece to its original position by screwing a large screw into it and lifting the screw with a pry bar or crowbar. Nail the lower piece to the upper piece by “toe nailing” 3” finishing nails into it. Toe nailing is hammering in nails at small angles for greater strength. Some of the nails are angled to the right and some are angled to the left.
Window Sill of Old House
1/8″ Thick Ribbed Profile EPDM Weatherstrip
    • To seal the gap below the sash, use 1/8” thick ribbed profile EPDM weatherstrip. EPDM is a type of rubber designed for weatherstrip. It is very durable and is elastic at sub-zero temperatures. 1/8” thick ribbed profile EPDM weatherstrip is the thinnest EPDM weatherstrip, it compresses to about 1/16″. If after you put it in the thumb latch doesn’t close, remove the part in the rear (the keeper), put two pieces of cardboard under it as shims and screw it back down. Cut the cardboard around the thumb latch using a utility knife. It is self adhesive, but copper weatherization nails should be used to add strength. For adhesion, the surface must be above 40 degrees and dry. If the temperature was cold earlier in the day, the surface may still be slightly damp from condensation, so dry it with a hair drier. Also, prepare the surface for adhesion by sanding it.
    • On the lower sash of wooden double hung windows, the top edge of the pane(s) of glass fits into a channel. They are designed this way because the bottom rail of the upper sash prevents the glass installer from applying glazing putty there. Glazing putty should be put into the channel before the pane is pushed in to prevent infiltration, but this is often not done. Check from inside if the channel has putty in it. If there is no putty, caulk the channel with indoor/outdoor siliconized acrylic caulk. This will not stick to the glass but will stick the wooden sash.

a
Weatherize and Repair Modern Vinyl, Fiberglass, Wood and Aluminum Double Hung Windows

Vinyl double hung window

“Modern double hung windows” refers here to any windows with spring balances in place of window weights. Spring balances have springs in long tubes. All very old, double hung windows have in place of spring balances large window weights hidden behind the window jambs, with sash cords and pulleys that are visible.

The weatherstrip can usually be easily replaced on modern double hung windows if you find matching weatherstrip. You simply remove the sash from the window opening, slide out the old weatherstrip and slide in the replacement piece.

“Vinyl windows” have hollow frames and are made from PVC, which is the plastic. “PVC windows” are also made from PVC but have frames that are solid, made from cellular PVC. Both types of windows are often called “Vinyl windows” because they are both constructed from the vinyl product, PVC.

Inexpensive vinyl windows are not all designed to be perfectly air-tight, so if you measure very slight infiltration from a vinyl window, it may not be repairable. Hollow frame vinyl windows are not as rigid as the other types of windows.

Left side of sash is closer to window sill than right side
    • If there is infiltration at the bottom of the lower sash and the weatherstrip on the sash is not worn or damaged, check if one side of the sash and not the other contacts the window sill, that is, check if the sash is slightly crooked. If the sash is crooked, mount 1/4″ thick self-adhesive low density foam weatherstrip tape to the window sill where the weatherstrip on the sash rests on it. Low density foam weatherstrip tape is very compressible, it will become paper thin on the side where the sash contacts the window sill. Before applying the tape, clean the surface by rubbing it with a scouring pad or sand paper.
    • If there is infiltration at the top or bottom of either of the sashes due to damaged or missing weatherstrip, try to order identical weatherstrip from the manufacturer. Other brands may make your windows hard to open or hard to latch or may not fit in tightly or may not seal the gap. Weatherstrip on the top and bottom of a sash is normally “kerf-style”, that is, it is inserted in a kerf, a thin slot in the sash. It may be vinyl or pile.  Below are some of the many shapes of kerf-style vinyl window weatherstrip used on the tops and bottoms of window sashes. bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

      Types of Vinyl Kerf Weatherstrip Used on Tops and Bottoms of Window Sashes

To replace a strip of vinyl weatherstrip, pull it out and push in the new strip. To replace a strip of pile weatherstrip, on most sashes you slide out the old strip and slide in the new strip.  On some sashes, however, there is no way to slide it out, but you can  pry it out using the tip of a knife. Insert the new piece by pressing it in with a “spline tool”. This has a wheel, and is designed to put in splines, which hold in screening. It is sold at hardware stores.

Bronze weatherstrip used above upper sash and on window sill

On wooden sashes, the weatherstrip on the top and bottom could be bronze weatherstrip nailed to the window sill and the frame above the window. It fits into grooves in the sash. If there is infiltration, the groove may be filled with debris or the weatherstrip may be slightly bent. 

    • If there is infiltration between the upper and lower sashes of a wooden window, check if it has interlocking bronze strips, one on each sash. They interlock to seal the gap. If they are bent, take out the bends. If there is pile or vinyl weatherstrip that appears worn out, replace it. If the sashes are not removeable, get access to the area of the weatherstrip by raising the lower sash and lowering the upper sash until the lower sash is higher than the upper sash.
    • If there is infiltration at the sides of a sash which has pile weatherstrip, replace the weatherstrip (the sides will not have vinyl weatherstrip). It can be replaced by any pile weatherstrip of very close dimensions, or you can use a strip with a wider backing by trimming the backing with scissors. Pile weatherstrip sold in some hardware stores and home centers is too thin (the pile is too short) for most windows. To slide out a piece of weatherstrip, you may need to remove the latch at the top of the sash. The latch is force-fitted in and can be pulled out with pliers. On some sashes you must pull out the weatherstrip with needlenose pliers and press in the replacement weatherstrip.
Bronze Weatherstrip
That Is Mounted to Window Jambs

If there is infiltration at the sides of a sash that has bronze weatherstrip mounted to the window jambs, try to smooth it out by knocking out the bends. Bronze weatherstrip is sometimes used on wooden windows. The weatherstrip fits into a groove in the wood. They are nailed on so if you remove them they are easily damaged. They are available through online suppliers if the window is not too old.




Energy Tips for Vinyl, Fiberglass, Wood and Aluminum Double Hung Windows

Aluminum trim with mortar joints correctly caulked
  1. Check outside of the house for missing caulk wherever the aluminum or vinyl trim meet the house wall.
  2. If you have brick walls, check the mortar joints. Do not caulk the mortar joints with polyurethane sealant because it is sloppy and can easily get smeared onto the bricks. If the caulking is cracked or falling off, scrape it off and replace it with an exterior sealant. See Types of Exterior Caulk and How to Apply Caulking. After scraping off the caulking and before replacing it, bend the trim away from the wall and look behind it to check if there is insulation, occasionally installers fail to put it in. To install insulation, cut strips from a roll of 3 ½” fiberglass insulation and stuff them in around the window frame. This material is sold at home centers and builders supplies.
  3. If you have vinyl windows and your home is relatively old, they are probably not the original windows and the installers may have used the wrong caulking for vinyl. Outside of the house, caulking seals the gaps between the vinyl window frame and the original wood or aluminum flashing. If the caulking appears to not stick well to the vinyl, scrape it all out and replace it with an exterior caulk that lists vinyl as a material it adheres to.
  4. There is a space above vinyl window frames that is covered by a movable piece of vinyl wrapped around the top of the window. Check if this has fallen down slightly. If it has, fill the gap with a very adhesive caulk, such as polyurethane sealant or silicone sealant to seal the gap and hold the piece of vinyl in place.
  5. If one of the top corners of the lower sash does not close tightly against the upper sash, the latch on that side of the sash is broken and should be replaced. Order a replacement latch from the manufacturer or from an on-line supplier, or buy it at a window repair store.
  6. Vinyl and aluminum windows may be installed with a wide aluminum sheet metal trim strip around them that contacts the walls of the house. This is normally done when the original wooden windows were replaced with vinyl or aluminum windows. The aluminum trim strip may be held in place only by caulking that sticks it to the wall of the house because it doesn’t contact the window frame. If it has broken loose from the wall, push it to check if contacts the window frame. If it doesn’t, use a thick bead of exterior sealant to re-attach it.
    Inserting pile with spline tool
  7. With vinyl windows, there may be a small gap between the side of a sash and the window frame at the top or bottom of the sash. Seal the gap by removing the pile weatherstrip and replacing it with thicker pile weatherstrip. This must be ordered online. To replace the weatherstrip, pry it out with a paring knife. Push in the replacement pile weatherstrip using a spline tool. These are available in hardware stores and are used to insert splines, which mount screening.
  8. Vinyl windows can have a small gap along the side of a sash if the frame is bowed. You may be able to close this gap by turning the jamb adjustment screws to move the window jamb. These are halfway up the window frame. Turn them clockwise slightly to close the gap. Don’t over-adjust them because you could crack the vinyl. If you cannot close the gap, replace the pile weatherstrip with thicker pile weatherstrip, which must be ordered online. To insert pile weatherstrip, see paragraph above.
  9. If you have double hung windows with vinyl jamb liners and air leaks past the side of the sashes, the jamb liner could be loose. Remove the sashes and pull out the jamb liner. Stick thick self-adhesive foam insulation tape to the back of the jamb liner. If it is tightly compressed it will push the jamb liner out slightly to close the gap.
  10. If a window sill is not level, causing a gap above it on one side, it can be repaired from the outside of the house. The window frame is not square. It is mounted in an opening in the wall that is larger than it and the wood shims it rests on were put in poorly. If the frame is not square, try to remove the vinyl or aluminum capping on the outside to access the shims. Replace them with thinner or thicker shims to make the frame square. In some windows, making the frame square is easy and in some it can be very hard.
  11. Outside of the house, check where the outer edges of the window frames meet the metal or vinyl trim. Check for cracks in the caulking. To re-caulk it, scrape off the old caulk using a sharp wood chisel and apply a thick coat of caulk. First, locate the two “weep holes” at the bottom of the window frame. These must stay open to allow rain water to flow out

 

 

Vinyl Window Frame with Aluminum Trim

a
Weatherize and Repair Old, Wooden Hinged Windows

If you have an old, wooden hinged window that leaks, it may need to be repaired, so try to repair it before mounting weatherstripping. Also, if you have to slam the window shut to close the latch, try to find the problem and fix it so members of your household don’t at times  leave it open. To repair it:

    • If the latch doesn’t close the sash tightly, the latch may be loose because the latch screws are in slightly rotted wood. If it is, replace the screws with longer or wider screws.
    • Check if several coats of thick paint is causing the problem. Large drops of oil paint on the side surface of the sash with the hinges will make the sash hard to close tightly. Scrape off the paint using a sharp wood chisel; if it is oil paint it is hard to remove. Repaint the bare wood. To avoid buying primer and exterior paint you could use “exterior paint + primer”. Also, check if loose paint fell off and is lying at the bottom, making the sash harder to close.
    • If the hinge screws are loose, replace them with longer or wider screws. They may be loose because the wood next to them is slightly rotten, so if you tighten them, they will become loose again. Replace them with 2” screws. If it is a basement window with hinges on the side of the sash, the hinges may be mounted to a board that is nailed directly to the foundation wall, so you can’t use longer screws. Replace the screws with wider screws. The screws’ heads will be wider than the holes in the hinges, so drill out the holes in the hinges to make them slightly wider.
    • If the hinges are on the side of the sash, and the bottom surface of the sash rubs against the window sill, try to repair it, because the people in the house may not always close the window. Check if the sash is out of square, causing it to sag. To repair it, try to raise the latch edge of the sash using a pry bar or small crowbar. If this makes the sash square, buy four 6”x6” flat corner braces and screw them on to strengthen the sash. Use 1” screws, not the shorter screws that are packaged with the braces.
    • If you have fixed the problems listed above and there is still infiltration, mount weatherstripping:
      1. Prepare the surfaces where the weatherstrip will be mounted. It should be mounted to the surface of the window frame where the hinges are mounted. On the other three sides it should be mounted to the window stop (see drawing). If the paint is not smooth, scrape it off with a sharp ½” wood chisel. Repaint it with “exterior paint + primer”. If the surface is smooth, sand it so the weatherstrip sticks well.
        nnnn
        bbbbbbbbbbbbbbbbbbbbbbWeatherstripping On Hinged Window
      2. On each of the four sides, use self-adhesive foam weatherstrip where the gap is very thin. Where the gap is larger use EPDM weather seal tape. This is made from a very durable material. Ribbed profile EPDM weatherstrip is the thinnest, it is 1/8” thick and can be compressed to about 1/16”. D-profile EPDM is ¼” thick and can be compressed to about 1/8” thick. The problem with using EPDM is that you may need to buy rolls of different thicknesses for different sides of the window, and a roll costs $5 to $6, more than the cost of the energy you would save. It is self-adhesive tape, but it should be nailed down at the ends with copper weatherization nails.

a
Weatherize Sliding Windows

    • If a sliding window with factory-installed weatherstripping allows infiltration, check if the weatherstripping is damaged or missing. You may need to buy weatherstripping that is designed only for that brand of windows because there are many shapes and sizes of weatherstripping used, such as the “kerf-style” bulb weatherstrip shown above. If you cannot order it from the manufacturer, remove a piece, measure its dimensions and order it on-line. Do not glue in weatherstrip that is slightly different, it will not stay attached.

      Aluminum Sliding Window

    • Some sliding windows are designed to be air-tight with no weatherstripping at the top or bottom. If these leak air they may not be repairable. Others have pile weatherstrip, which is replaceable. The picture shows an aluminum sliding window with pile weatherstrip.
    • If the channels above and below the sashes are bent, allowing infiltration, you may be able to replace them but replacement channels are available at some home centers and building supply stores.
Thin Foam Self-Adhesive Tape
    • Gaps between the sides of the sashes and the window jambs can be sealed using 3/16” thick self-adhesive foam weatherstrip, but this is not as durable as the weatherstrip supplied by the manufacturer. The other types must be nailed on and you cannot nail into vinyl, fiberglass or aluminum. Also, it compresses to be paper-thin, which is necessary for the latch to close. To mount self-adhesive weatherstrip, thoroughly clean the surface with rubbing alcohol, because this dries fast, or sand it and wipe off the dust.
    • After mounting weatherstrip to the jambs, if the latch doesn’t close, remount the latch if possible. Many are similar to the thumb latch on a double hung window, with a rotating part in the front and a “keeper” in the back. If it is this type, take off the keeper and remount it with two pieces of cardboard between it and the sash.

Weatherize Old Wooden Sliding Windows with No Weatherstripping

If you have old, wooden sliding windows with no weatherstripping, mount weatherstrip to the window jambs where it will be compressed by the sashes, and to one of the rails where the sashes meet.

    • If the weatherstrip mounted to the jambs must be compressed paper-thin for the latch to close, spring bronze weatherstrip is good for this purpose. It is made from a durable material and it is not held on by adhesive, so it will last very long. To mount it, it is best to use a brad driver because hammering in that location would be difficult. Check that the surface of the sash that compresses against it is very smooth to make an air-tight seal.
    • If the weatherstrip mounted to the jambs must be compressed paper-thin, you could also use 3/16” thick self-adhesive foam weatherstrip tape. To mount this onto a window jamb: Sand the surface of the jamb if it is rough or dirty, or wash it with rubbing alcohol, which dries quickly. If the temperature is cold, dry off the surface with a hair dryer because condensation may be on the surface. Stick it on and staple down the ends using a heavy duty stapler.
    • Mount weatherstrip to one of the rails where the sashes meet. Either spring bronze weatherstrip or tubular vinyl weatherstrip could be used. Spring bronze weatherstrip is not completely air-tight. It is not attractive but would only be seen from outside the house. It will fit in a very narrow gap between the sashes. Nail it on with a brad driver rather than a hammer because hammering could cause window putty to fall out or break the glass. If the latch does not close after mounting the spring bronze, remount the smaller piece of the latch (the keeper). Remove it and put two pieces of cardboard between it and the sash, clamped between the keeper and the sash. Tubular vinyl weatherstrip should also be nailed on with a brad driver.

Pile Weatherstripping

Pile weatherstripping is the best type for old, wooden sliding windows, but it is the hardest to mount. It is very durable, doesn’t make the windows harder to open, and can seal very narrow gaps. To mount it you must remove the sashes and cut channels. This type, unlike the others, can be mounted to the top surfaces of the sashes. This is a do-it-yourself project, but you must have a plunge router or a table saw to cut the channels. Plunge routers are better for this and are not expensive.

Brad driver

Tools and Materials to Mount Pile:

    • plunge router or table saw
    • brad driver or hammer and needle nose pliers to hold nails
    • brass weatherization nails
    • epoxy
    • pile weatherstrip, base approximately ¼” wide and the pile should be as short as possible, approximately .350”

Procedure:

    1. If possible, work on a day that is not cold because the epoxy may have a requirement that the temperature be 50° for many hours to dry.
    2. Remove the sashes. The sashes may be removable from the center of the window opening.
    3. Find a lead-safe work zone such as outdoors or in a garage with open doors. Also, wear a mask. Old wooden windows normally have lead paint as their original coat of paint.
    4. Cut channels for the weatherstrip. Cut them on the surfaces that contact the sides of the window jamb. Cut one on a surface where the sashes meet and cut them on the sides of the sash at the top and bottom. A router is the best tool for cutting the channels but a table saw could also be used. Cut them 1/8” deep and the width of the weatherstrip’s backing, which may be 1/16”.
    5. Glue in the pile with epoxy. If it is a cold day, you may need to leave the sashes inside all day as the epoxy dries.
    6. Put in a brass weatherization nail in each end of each piece of weatherstrip. This will hold the ends in place while the epoxy dries and also add bonding strength. These nails have notches to hold better.
                 Pile Mounted to Sliding Window Sashes                       

hhhhhhhhhhhhhhhhh
Insulate Old Metal Sliding Windows with No Weatherstripping

If you have a very old, metal sliding window in a metal frame, which never had weatherstripping, mount 3/16″ thick foam self-adhesive weatherstripping to the jambs. This is the only type of weatherstripping that is sufficiently compressible. Before sticking it on, lightly sand the jambs to remove rust or corrosion. If it is a cold day, dry the jambs carefully with a hair dryer. Also, mount weatherstripping to one of the rails where the sashes meet, but not where a rail would slide against it, because it would not last. Mount it on one rail for the other rail to barely contact when the window closes.

nnnnnnnnnnnnnnnnnnnnn
Weatherize and Repair Casement Windows

Casement windows, also called “crank-out windows”, are opened and closed by a crank. Each window has a single sash which swings open and is held in place by a steel arm. They have advantages over double hung windows; the entire window can be opened to allow more air to enter, and they can direct air into the house when the wind blows.

Normally, they swing outward but some smaller casement windows now sold swing inward. They normally open from the side, but there are small casement windows that open from the top, call hopper windows, and from the bottom, called awning windows. Old casement windows have steel frames, because the frames must be strong enough to support them when a strong wind blows. All modern casement windows, unlike old steel frame casement windows, have factory-installed weatherstripping.

Old, Steel Casement Windows

Old Steel Casement Windows

Many of the homes built in the mid-twentieth century had casement windows with panes of glass in thin steel frames. These normally become drafty because they have no weatherstripping and they can become rusty and slightly bent. First, try to restore them to make them close tightly with a minimum of infiltration, and then mount weatherstripping. Also, check for visible gaps between the steel frame and the wall. If there are gaps, caulk them on the outside with silicone caulk and on the inside with a paintable caulk.

The weatherstrip can only be stuck on and will not be durable. First, use a sharp ½” wood chisel to scrape off the rust, dirt and paint that prevent the sash from closing tightly. After scraping off the paint, paint the bare metal with metal primer and a high quality exterior paint.  If the sash still does not close tightly, there are several ways to repair it:

    • If the crank assembly is hard to turn, it may be slightly rusty. Spray in WD-40 lubricant. If this fails, disassemble it and replace the grease on the gears. Grease for gears is sold at auto parts stores.
    • Replace the crank assembly (operator). Those available at home centers only fit newer casement windows. Take the crank assembly to a window repair store and ask their technicians if it can be replaced, or do an online search.
    • If has a broken locking handle, replace it. This will probably need to be ordered online.
    • With some windows, inserting a cardboard shim between the locking handle and the frame will cause the sash to be pulled more tightly against the frame.

If the sash closes tightly and air leaks around it, there are several ways to seal the gap:

    • First, prepare the contacting surfaces thoroughly. Scrape off any rust with a wood chisel. If bare metal is exposed, paint it with metal primer and high quality exterior paint. Lightly sand the areas that were not painted to clean them, and wipe off the sanding dust. If the weather is cold, thoroughly dry the frame with a hair dryer because warm, inside air creates condensation on a cold surface. bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    • One way to seal the gap is to use clear silicone caulk to create a form-fitted gasket. Put packing tape over the sash’s surface that will press against the window frame so the silicone won’t stick to it while it is drying, because silicone does not stick to it’s waxy surface. Apply a thick bead of clear silicone caulk to the window frame where it will be squeezed to the shape of the gap when you close the window. If the packing tape sticks to the caulk, put a strip of wax paper between the sash and the silicone and close the sash onto it; silicone does not stick to wax paper. You could also try brushing powder, such as flour onto the tape. bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    • Another way to seal the gap is to stick 3/16” thick, foam weatherstrip tape to the window frame. This is not durable, but it can be compressed paper-thin.

If it cannot be made to close tightly and it will not be opened in the winter, there are ways to seal the gap while the window is closed in winter.

    • Caulk around the edges of the sash with “removable weatherstrip caulk”. This is designed to be applied at the beginning of the heating season and be easily removed at the end of the season. It is available at hardware stores and home centers. bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
    • Cover the window openings with shrink film. This is mounted for the winter only. It prevents all infiltration if applied well and leaves the windows transparent. It is mounted to the frame so it creates a dead air space between the shrink film and the glass, which increases the R-value of the window. It is thin plastic sheeting that is taped to the frame with double-face (double sided) tape. After taping it on, heat it with a hair dryer, causing it to shrink very slightly to become transparent. It can be reused for several years but is it less transparent each year and you must replace the tape. Shrink film is available at home centers and hardware stores. Double sided tape is sold in drug stores and home centers. Plastic drop cloth can be much thicker than shrink film, but it does not insulate better because the surfaces create the resistance to heat flow.

Wood, Vinyl, and Aluminum Casement Windows

Modern Aluminum Casement Window

 Wood, vinyl and aluminum casement windows have sashes with thick frames and weatherstripping on the sash or the window frame. If air leaks around a sash:

    • If it leaks because it does not close tightly:
      • Check if the crank is mounted crooked. The wood may be rotten next to the screws that support the crank. If it is crooked, remount it using longer or thicker screws. bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb
      • Check if the bottom surface of the sash rubs against the window frame due to large drops of paint. Scrape the paint from the bottom surface of the sash and from the window sill. Repaint the two surfaces. To avoid buying primer and exterior paint you could use “exterior paint + primer”. bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb 
      • Check if the bottom surface of the sash rubs against the window frame because the sash is sagging. This should be fixed because it will probably get worse until someone breaks the crank by turning it too hard. Some casement windows have adjustment nuts that allow you to raise the sash slightly. There may be one at the bottom where window sill rests on the channel or where the crank assembly rests on the window frame, or possibly somewhere else. There will be one at the top that you should adjust if you adjust the nut at the bottom. If there are no adjustment screws, raise the sash slightly by putting a shim under the channel that the sash slides on. If it cannot be raised, use a belt sander or wood plane to sand or plane the bottom of the sash. Paint the bare wood.
Wood Casement Window
    • If a wood, vinyl, or aluminum casement window is closing tightly and has air leaks, try to replace the weatherstrip with identical weatherstrip. It will probably have to be ordered from the manufacturer or from an online supplier of weatherstripping. Other types of weatherstrip would probably not be durable or air-tight.
    • If a window leaks and you cannot buy identical weatherstrip, mount thin foam weatherstrip to the frame, such as 3/16” thick foam self adhesive weatherstrip tape. This is not durable, but it can be compressed paper-thin. Before applying the weatherstrip on a cold day, dry off the frame with a hair dryer. The warm air in the house deposits condensation on a cold window frame. After drying the frame, clean it with rubbing alcohol because this dries quickly, or sand it with fine sand paper. If the frame is wooden, staple the ends of each piece of weatherstrip with a heavy duty staple gun because self adhesive weatherstrip comes loose at the ends.

Energy Tips for Casement Windows

    • Insulate casement windows by mounting shrink film. On windows you open, mount it to the frames of the sashes. On windows you don’t open you could mount it to the the wood window trim (casing) to seal any gaps around the sashes. To mount shrink film:
      1. If you mount it to the frames of the sashes on a cold day, dry the frames thoroughly with a hair drier because they will be slightly damp from condensation.
      2. Clean the surfaces where the shrink film will be mounted. If you use rubbing alcohol, they will dry quickly.
      3. Mount the shrink film following the instructions given. A hair drier must be used. Be careful not to overheat the film.
      4. To re-use the shrink film the next heating season, mount it with “double-sided tape”, which is sold in drug stores.
    • If you don’t open your casement windows because they have no screens, build screens from a kit. Opening your casement windows can allow you to use less air conditioning.  A casement window “scoops wind into the house” when wind blows  along the wall of that window.  Screen kits are sold at hardware stores and home centers.
      How to insulate windows

      Corner key

  •  
    • If you don’t open some of your casement windows because their screens are broken, try to repair them. If the corners are broken, replace the “corner keys” which join the frame at the corners.  There are many models of corner keys, but window repair stores and online suppliers should have the ones you need.

a
Weatherize Fixed Windows

“Fixed windows” are windows of any style that are not designed to be opened. Large picture windows, for example are fixed windows.

Energy Tips for Fixed Windows

    • If you find an air leak around a fixed window, caulk it from the outside if possible. This will prevent water from entering and rotting the frame of the sash or entering the wall. The wood outside of a house may be damp for days after a rain from trapped water. A few exterior caulks, such as silicone sealant, are formulated to stick to damp surfaces. This will be written on the label. If you caulk from the inside on a very cold day, the window frame will be cold, causing slight dampness from condensation, and interior caulk does not stick to damp surfaces. Dry the area with a hair dryer before caulking. See Types of Exterior Caulk and How to Apply Caulking
    • If you have fixed vinyl windows or vinyl-covered wooden windows which are next to each other, check for infiltration where their frames meet. The seam between the frames is covered by a vinyl U-shaped channel, inside and outside of the house. Air may leak around it and between the two frames. If you find an air leak, caulk both sides of the U-shaped channel. Caulk it with an exterior sealant with vinyl given as one of the materials it adheres to because many exterior caulks do not adhere to vinyl.
Fixed vinyl windows. The gap between them is covered by U-shaped channel
    • If air leaks in from under the sash because it has rotted away there, repair the rot damage. The most durable product for repairing rotted wood is “epoxy wood filler”. The instructions indicate how thick an area of wood it is designed to fill, so try to cut out only that thickness of wood. After repairing the sash, prime it, and paint it with high-quality oil-base paint to prevent further damage.
    • If it is a single-glazed fixed wooden window with infiltration around the edges of the glass, replace the window putty.
      1. Buy glazing putty. Read the instructions before removing the old putty. The weather conditions may not be acceptable for glazing.
      2. Scrape out the glazing putty with a sharp 1/2 “ wood chisel. Be careful not to break the glass (don’t use a hammer).
      3. Apply the window putty using a 1” flexible putty knife.
      4. When the putty has dried, paint it with oil-base paint. The number of days required is given on the container. This will seal the crack between the putty and the glass to prevent water from entering, freezing and breaking out the putty.

a
Temporary Ways to Weatherize Windows

How do you insulate windows that you don’t open all winter for just one winter? There are many quick and easy ways to insulate them. All of the methods explained below are done from inside the house. If you install temporary insulation from the outside using staples or small nails, you would leave holes in the wood which would allow rot. If the insulation were taped on, the wind would tear it off.

    • If a room has single glazed windows, make it warmer in the winter by inserting a tightly-fitting piece of thick rigid foam insulation into each window opening. This may not be a good investment for lowering your heating costs, but it would make the room warmer. The insulation panels are sold as 4 ft. x 8 ft. sheets in the building materials departments of home centers. Most brands of rigid foam insulation cannot be used because they emit noxious fumes in a fire, but these all have warnings on their labels such as “This product should be separated from the building interior by a thermal barrier, usually ½” gypsum board”. Draw the curtains to cover the insulation from sight. If the pieces of insulation don’t fit tightly and fall out, tape them in with painter’s tape, which is designed not to damage the paint when removed. 
    • If a room has single glazed windows and no storm windows, you could make the room warmer in the winter at almost no cost by making insulating panels from one or two pieces of corrugated cardboard to fill the window openings. Corrugated cardboard has air spaces, which create dead air insulation.  Some small grocery stores will give customers large cardboard boxes. 

Materials and Tools:

    • 48” T-square or 48” straight edge and framing square
    • Utility knife
    • Large sheet of plywood or long, wide board to lay cardboard on while cutting with utility knife
    • Tape measure
    • Duct tape
    • Glue
    • Cardboard from large cardboard boxes, enough for three panels for each window opening

Procedure:

      1. Cut three pieces of cardboard for each window to fit tightly into the window opening.
      2. Cut 1”wide strips of cardboard to glue around the edges of the pieces of cardboard as spacers.
      3. For each window panel, glue the 1” strips around the edges of two pieces of cardboard.
      4. Form each window panel by taping together three pieces of cardboard with duct tape, separated by the 1” wide spacers.
      5. Insert the window panels in the window openings. If they don’t fit tightly, tape them in with painter’s tape to hold them in and block infiltration.
    • Fill gaps around sashes by caulking them with removable weatherstrip caulk. This is easily peeled off as a long string at the end of the heating season, and is transparent. It is sold in paint departments.
    • Mount roller shades or use ones that are there; pull them down and tape them along the sides. This will trap the cold air behind them if you thoroughly seal them on all four sides. Clear weatherization tape is very strong but may damage the paint, so the frame may require a small touch-up when you remove it the tape. Permanent double sided tape is not as durable but is not unattractive attractive because it would be hidden behind the shades. It does not damage the paint. Tape the shades on tightly because air will escape through a small gap due to the force of convection. Seal the gap between the roll at the top and the window frame with a rag or with tape.
    • Fill larger gaps around old, drafty wooden sashes by stuffing in either 3/8” diameter foam caulk backer rod or self-adhesive foam weatherstrip tape.
    • Cover the windows with shrink film. This is also called an “indoor window insulation kit”. It prevents all infiltration if mounted carefully, and leaves the windows perfectly transparent. It is mounted to the frame so it creates a dead air space between it and the glass, which increases the R-value of the window. It is thin plastic sheeting that is taped to the frame with double-sided tape. After taping it on, heat it with a hair dryer, causing it to shrink very slightly to become completely transparent. It can be reused for several years but is less transparent each year, and you must replace the tape each year. After the first year, buy double sided tape, sold in drug stores. Shrink film is available at home centers and hardware stores. Shrink film kits for large picture windows are available at some home centers.

To mount shrink film:

      1. If the air is cold, dry the window frame surface with a hair dryer. It may be slightly damp from condensation.
      2. Clean the window frame surface with rubbing alcohol because it dries quickly.
      3. Mount the shrink film using the instructions given in the package; be careful not to overheat the film.
Bubble Wrap
    • Cover each pane of glass with bubble wrap. This could be done in addition to mounting shrink film. It creates good insulation and allows light to enter the room. It has large, round pockets of air that are designed to protect objects when they are shipped, which create good dead air insulation.

Cut a piece the size of each pane of glass and stick it to the glass; no adhesive is needed. First, clean the pane. Mix water and a small amount of dish soap, and spray it in a thin film onto the flat side of the bubble wrap, and press it against the glass. For better insulation, tape it on with the bubble side facing the glass. This will create a dead air space between the flat side of the bubble wrap and the glass, in addition to the spaces in each bubble. Tape it on with clear, ½“ double-sided tape. This is sold in drug stores and home centers.

    • Twist plastic wrap (kitchen wrap) into rope form and stick it into the gaps around the sashes with a butter knife. Leave 2” hanging out at the end of each piece to pull it out.

a
Heat Control Window Film and Reflective Window Film

Applying Heat Resistant Film

Heat control window film and reflective window film are thin, plastic films which you mount directly to the glass. Some require gluing, but most stick on by “static cling”. Reflective window film resists the flow of heat into the house by blocking UV radiation, the form of radiation which transfers solar energy. Sun tan lotion is designed to block UV radiation. “Heat control window film”, also called “all season window film” is reflective to block UV radiation and also “low-E” to resist infrared radiation. Infrared radiation carries heat energy from the warmer side of the window to the cooler side. Low-E stands for “low emissivity”.

“Low-E window film” blocks only infrared radiation. It is not often found in stores. Reflective window film and heat control window film are available at home centers and hardware stores but in a very limited selection. A home center may have only one heat control window film and it may darken the rooms more that you want, but they may have others which you can have sent to their store for pick up. Installation instructions are given in the packages. Some manufacturers have a wide selection, but most if not all require that their installers put up their film, which would greatly lengthen its payback period. Any window film can also be mounted onto patio doors. The prices of window films are in the range of about $30 to about $40 for a roll large enough to cover about three windows.

Any window film can be used to correct temperature imbalances in your home. If, for example, a room is too hot in the summer, reflective window film could be mounted to those windows only.

Reflective Window Film

Reflective window film, also called “solar window film” is designed to block UV radiation to keep your home cooler in summer. It also gives you privacy by preventing persons from seeing into your home. UV radiation is also called “solar radiation”. It transfers the energy of sunlight through glass. There are two basic types of reflective window film:  “mirror reflective” and “tinted reflective”. Mirror reflective film looks like a mirror from outside the house. It is fairly transparent from the inside the house, except after dark. It should not be installed on a north-facing wall because there it would not be effective.

Some reflective films can be easily removed after the winter months are over and reused each year. These are installed by “static cling”.

Some homeowners choose reflective window film because it prevents persons from looking into their home during the day. However, at night persons can see in when lights are on. Some choose it because it can reduce glare on TV and computer screens. It may help to prevent furniture damage caused by fading, but it may prevent some house plants from receiving enough sunlight.

The instructions for some brands of double pane windows warn that reflective film may damage the window, due to the heat. The instructions for other brands of windows indicate that reflective film is safe to use. When the sun is shining brightly, the film, which is on the inner pane, reflects much UV radiation back to the outer pane, making the gas between the panes very hot.

Reflective window film can be mounted on low-E windows. It will effectively block UV radiation. Low-E windows have factory-installed coatings to resist infrared radiation. These coatings are similar to those on Low-E window films.

Tinted Reflective Window Film

Windows Covered With Tinted Reflective Window Film

Tinted reflective window film reduces the light that enters a room, slightly darkening the room. Some manufacturers offer a range of these films, from film that reflects the least UV radiation and is virtually invisible from inside the house, to film that reflects the maximum UV radiation and makes the room noticeably darker. The manufacturers that offer a range of films may require that their installers mount the film. Some home centers offer a range of these films, but only one will be at their stores. The others you can request to be sent to the store for pick-up.

Mirror Reflective Window Film

Mirror reflective window film

This is the most effective way to block UV radiation and keep the home cooler in summer. It is also called “one-way mirror window film”, “one-way privacy daytime window film” and “mirror silver privacy window film”. It has the appearance of a mirror from the outside and is fairly transparent from inside the house. Mount it on the windows that the sun shines directly through. It can be most effective on east- and west-facing walls because the sun shines in at a lower angle. Most, but not all of these films have the problem that after dark, persons inside the house cannot see out, although persons outside can see in if the lights are on. There are films that are designed to solve this problem, which can be ordered online. Mirror reflective window film is available at some hardware stores.

Heat Control Window Film

The name, “Heat control window film” is given to window film that is reflective to block UV radiation and also has a low-E coating to block infrared radiation. Its manufacturers call it by different names, but it will be described with phrases such as “blocks UV rays” and “low-E coating to retain winter heat”.

Low-E coating is a thin layer of microscopic particles of metal or metal oxide which blocks infrared radiation. Infrared radiation transfers heat energy from the hotter to the cooler side of the window.  Thus, low-E coating holds heat in the house on cold days and keeps out the heat on hot days. This low-E coating is the same coating that is applied to low-E windows.

Low-E stands for “low thermal emissivity”.  A material’s emissivity is the measure of how much infrared radiation will pass through it. The emissivity is about 30% for some window films.

Heat control window films are available in a range of clarities. The films with the lowest clarity provide the best insulation but make the room noticeably darker. Your local hardware store or home center may carry only one heat control window film. To know which clarity is best for you, you may need to buy a package and mount it on the windows of one room. Films that are mounted by static cling can be easily removed. If it makes the room too dark you may be able to order a different film from that manufacturer. The websites of some window film manufacturers show how much a room is darkened by each of their films, and give the emissivity, i.e., effectiveness at blocking heat flow, of each film. The websites will also tell you the dealer closest to you, but the dealers may require that they put on the window film.

Before buying a heat control window film, try to find its product details on the manufacturer’s website. These will give the emissivity of the film. A film with a low emissivity such as .30, allows only 30% of the infrared radiation to pass through. Some heat control window films are very hard to look through from inside after dark.

On the website of one manufacturer, they claim that their “clearest window film” will allow 70% “visible light transmittance” when used on a single-pane window. Their window film with “highest energy savings”, used on a single-pane window allows only 33% visible light transmittance. On the website of another manufacturer, they claim that their window films have a “visible transmittance” ranging from 31% to 59% for various films when used on single-pane windows. This is how well you can see through the window. They also give the emissivity of each film.

How Much Could You Save in Utility Costs By Installing Window Film?

The Department of Energy has considered window film a “top-tier technology for energy conservation with one of the fastest paybacks”. The proof of its effectiveness is that many utility companies offer incentives for installing it.

Window film is effective on double glazed windows, especially at blocking UV radiation. A study published by The International Window Film Association in several cities in California (where UV radiation is relatively high), reported that the return on investment varies greatly among houses for both single pane and double pane windows, and that it was higher in cities in hotter climates such as San Diego. The returns on investment for insulation installed on double pane windows were, on average, more than half as high as on single pane windows. Their study concluded that, though return on investment varies greatly, it is often about two years in hot, sunny regions of the state for single glazed windows.

There are too many factors to estimate how long it would take to recover your investment in window film, but it is a relatively good investment if certain conditions apply in your home, such as:

    • Relatively high direct sunlight and hot climate. Closing your curtains or blinds on the windows with much direct sunlight does little to prevent solar energy from entering your home. It enters through the glass and heats the curtains or blinds, which radiate heat into the rooms.
    • Your winter months are very cold and you have single pane windows. Heat control window film or low-E window film would be a good investment, unless you have thermal curtains or blinds that are designed to trap the air behind them. Closing curtains or blinds that do not trap the air behind them does not insulate the windows well because this air flows out in a convection cycle. If the air is trapped behind the curtains or blinds it becomes cold and doesn’t emit as much heat energy through the glass.

a
Solar Screens

Solar screens are close weave screens that block most of the light from entering through a window. They are installed mainly in the hottest, sunniest regions of the country, by homeowners who need to lower high air conditioning bills. They can be removed when the summer months are over. Their disadvantages may outweigh their advantages in other regions of the country.

Solar screens can be confused with “solar screen shades” and “solar shades”, two names for roll down shades that are installed inside the house.

Pros and Cons of Installing Solar Screens

    • Like mirror reflective film and the darkest reflective film, they greatly reduce air conditioning costs. But, unlike reflective film, solar screens can be removed after the summer months.
    • If you order solar screens and install them yourself, they may cost approximately $50 each. This is much less expensive than replacing your windows with low-E windows, but more expensive than mounting reflective window film.
    • In winter, they reduce wind-chill. This could lower your heating bills if it is windy where you live.

Disadvantages:

    • They make the home less attractive from the outside.
    • If left on throughout the year they block UV radiation in winter, which helps heat the house. Your heating bills could become slightly higher. 
    • They significantly darken the inside of the home.
    • They are more likely that other screens to be torn off by strong winds because at the same wind speed the force on them is much greater than on conventional screens.
    • They reduce airflow into the home, allowing less ventilation.

Kits to build solar screens are available online. The suppliers offer screens in black, tan and gray. You cannot replace the fiberglass or aluminum screening you have with solar screen fabric and use the same frame because the channels are too narrow. One online supplier advertises a kit for about $32 which is described below:

    • choice of frame color
    • choice of screen color (black, tan, light gray)
    • spline roller tool (to mount spline and screen into frame)
    • 4 pieces of heavy duty frame
    • 4 external solid corners (no miter cuts required)
    • 2 slide-in corner leaf springs
    • 2 lift tabs
    • spline (rubber tube that holds screen into frame)

With a lot of work I’m sure you can lower your heating and cooling bills greatly without replacing your windows, by using methods and energy tips in “How to Insulate Windows of All Types”.

Pin It