This guide shows many ways for do-it-yourselfers to weatherize windows of all types. It explains different types of window coverings and screens you can put on yourself to reduce the heat flow into your home and lower your air conditioning bills. bbbb bbbbb bbbb bbb bbb bbbb bbbb bbbbbbb bbbbbbbbb bbbbbb bbb

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, you will know how to  re-do it when the weather strip wears out if you did it yourself. Windows with 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.

First, here are a few definitions. Infiltration is air Air leaking into or out of a house. A sash is a panel that has one pane of glass or many small panes of glass. A double hung window has an upper and a lower sash which you can slide up and down. A fixed window has a single sash that does not open. A primary window is any window which is not a storm window.

Before checking a window for air leaks (infiltration) testing a window that has a storm window, open its storm window if it has one. Windows with storm windows should be checked for infiltration, partly because the storm windows may be left open occasionally. Also, because strong winds will draw air out of the house through gaps around the primary windows and the storm windows. 

Seal the Visible Gaps Before Testing for Air Leaks

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.

To caulk vinyl windows, see  How to Insulate Modern Vinyl, Fiberglass, Wood, and Aluminum Double-Hung Windows .To caulk outside the house, see  Types of Exterior Caulk and How to Apply Caulking.

1. Cut through the paint along the edges of the window stop.
2. Pry off the window stops with a stiff putty knife.
3. Nail the window stops back on. First nail in two nails and check if the window opens easily before nailing in the rest of the nails.
4. Caulk around the window stop with white, interior caulk.

Test for Air Leaks

1)  Hang a thin strip of tissue paper and check if it flutters. It will flutter if air is leaking in or out.

2)  If the outside air is cold, moisten your hand and check for cold air.

3) The most accurate way, in winter or summer is by using an incense stick. If the flame doesn’t rise straight up, air is leaking in. 

Candles are less effective because their smoke can be almost invisible. Incense sticks are sold at large discount stores.

4)  Use a “spot thermal camera” These are inexpensive if ordered from a home center. They can be used all over the the home.

5)  Use a “smoke pencil” (smoke pen). These emit powder to detect slight air movements. They normally must be ordered.

Check Storm Windows for Air Leaks

There are many small things you can do to insulate your windows.

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.

higher level by putting a shim or several pieces of cardboard under it. A shim can usually be cut from a paint stirring stick. Replace the screws with longer screws, such as 1¼” drywall screws.

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 fell out on one edge of the pane because the pane was not 

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.

1. Chisel out the putty with a sharp wood chisel.ssssssssss sssssssss sssssssssss s sssssss ssssssssss
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.sss sssssss sssssssss sssssssssss sssssss
3. If the putty fell out on one edge of the pane because the pane was not 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.

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. 

1) 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.

2) 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

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 weather strip. 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 with “window and door caulk”.

To insulate that window, mount vinyl bulb weather strip (tubular vinyl weather strip) all around the window frame. It should be used because it is more durable than felt or foam rubber weather strip. It is not self adhesive, so it must be stapled on or nailed on with brass weatherization nails. These are sold in the weatherization section of home centers and hardware stores.

How to Caulk Windows

1)  If you are replacing old caulking, use a sharp wood chisel or a stiff putty knife and thoroughly scrape it out. Some types of caulk do not stick to others. Also, the old caulking may be too dirty 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. 

 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 force the caulk into the gap.

3) Check for “weep holes” at the bottoms of sashes and avoid covering them with caulk. These must stay open. If closed, water would be trapped when the screen is closed.

4) 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.

5) 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”

Silicone Sealant

Polyurethane Sealant

All Weather Sealants

Insulating old, drafty wooden double hung windows lowers your utility bills and can do several other things. It may prevent uncomfortable cold drafts, it may make your home quieter, and it may prevent water from entering the walls, damaging the walls.

How to Seal the Gap Between the Upper and Lower Sashes

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.b

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.  ssssss sssssssss  ssssssssss ssssss 

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.  ssssss  sssssss sssssssssssssssssssssss 

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.

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 weather strip to the sash, see, How to Remove and Replace Window Stops and Mount Spring Bronze.

How to Remove and Replace Window Stops and Mount Spring Bronze Between the Sashes

TOOLS AND MATERIALS:

STEPS:

1. Cut the paint along the edge of the window stops. ssssssssssssss ssssssssss sssssssssssss sssssssssss 
2. Use a stiff putty knife or paint scraper to pry off the window stops. Be careful not to nick the wood.sssssssss ssssssssss ssssssssssssss sssssssssss sssssssss 
3. Move the lower sash away from the upper sash enough to mount weather strip 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. ssssssssssss sssssssssss sssssssssssss sssssssssss sssssssssss
4. Using shears or sharp scissors, cut a piece of weather strip.ssssssssssss ssssssssssssssss ssssssssssssss ssssssssss 
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.ssssssssss ssssssssss ssssssssssss sssssssssss sssssssssssss sssssssss
6. Check that the weather strip has been mounted with no bends. If it has a bend, replace it.ssssssssss ssssssssssss ssssssssssssss ssssssssssss ssssssssssss 
7. Carefully bend the weather strip away from the sash, without causing permanent waves in it. It is initially flat but must be bent out to contact the sash.sssssssss ssssssss ssssssssss ssssssssss ssssssssssss sssssss
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.sssssssss sssssssssss ssssssssssss ssssssssss sssssssss
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. ssssssssssss ssssssssss sssssssssssssss ssssssssss ssssssssss
10. Caulk where the window stops meet the window frame.

How to Seal a Gap Under the Lower Sash

Types of Weather Strip to Mount to the Bottom Surface of a Lower Sash

STEPS:

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 copper weatherization nails, which should be in the package (tiny nails are called wire brads). Use either a hammer with needle nose pliers to hold the nails, or 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”.

5)  Close the window and check that the thumb latch closes.

6) If the thumb latch doesn’t close, remount the part in the rear (the keeper) at a higher level. Mount it on a piece cut from a paint stirring stick, or on a few pieces of cardboard. Replace the screws with longer screws if a paint stirring stick is used.  

How to 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. These ways are explained below.

How to Mount Tubular Vinyl Gasket Weather Strip to the Window Frame

1)  Staple the weather strip 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 weather strip will wear out much sooner.

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

How to Insert Spring Bronze Weather Strip Between the Sash and the Window Frame on Each Side

Spring bronze weather strip is mounted by nailing on one edge and bending the weather strip away from the wooden surface. It is common on windows of very old homes that had no storm windows. It has advantages and disadvantages over the other good types of weather stripping.

Advantages and Disadvantages

TOOLS AND MATERIALS:

STEPS:

1. How to Use a wood chisel or sandpaper to smooth the surface of the window jambs where the weather strip will be mounted.
   
   
2. Use metal shears or sharp scissors to cut one piece of weather strip an inch longer than the height of the sash. Only one weather strip 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 weather strip 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 weather strip. 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 strength. Lower the sash and put nails in at the top.
   
   
7. Bend the weather strip 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 weather strip on the other side. If the window is not hard to open, mount a weather strip 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.

How to Mount Pile Weather Strip to the Sides of a Window Sash 

Pile weather strip, also called “brush weather strip”, may be the best weatherization material for wooden double hung windows. It is very durable and doesn’t make the windows harder to open, but is the hardest to mount.

You must remove the sash and cut channels for it. This is a do-it-yourself project, but you must cut the channels with a plunge router or table saw. Plunge routers are better for this and are not expensive. 

Pile weather strip 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 weather strip with a base approximately ¼” wide and thickness of about 5/16” (.312”) or 350”. (The pile weather strip sold at hardware stores is less than 5/16″ thick).

If the supplier does not indicate the adhesive to use or what the backing is made from, test several brands of epoxy. Glue a piece of the weather strip to wood and check how hard each is to remove when it is dry. 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 weather strip. 

There are advantages and disadvantages to using pile weather strip:

TOOLS AND MATERIALS:

STEPS: (lower sash only)

1. Work on a day that is not cold if this is possible. The epoxy may have a requirement that the temperature be 50° 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. Cut the channels in a lead-safe work zone such as outdoors or in a garage with open doors. Old wooden windows often have lead paint as their lower coats of paint. Also, wear a mask.
   
   
6. Cut channels for the weather strip. 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 weather strip to hold down the ends. This will hold the ends in place while the epoxy dries and also add bonding strength.

How to Remove the Window Stops and Remount them Closer to the Sash

If a sash rattles when the wind blows, 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:

STEPS:

1)  Cut the paint where the window stops meet the window frame.sssssssssssss 

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 surfaceof 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 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.

Install a “Side Window Lock” on Each Side of the Sash

a “ side window 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.

How to Insulate Windows with Windowsills That Are Not Level

If your home is very old, some of the windowsills may not be level because the home’s foundation has settled or the wall frame below the windowsill is badly rotted.

STEPS:

1) Cut the beveled piece of wood to one end the thickness of the gap and the other end paper-thin. 

2) Sand the bottom surface of the sash with a palm sander or sanding block to remove the paint. sssssssssss ssssssss

3) Glue the piece of wood to the sash with polyurethane construction adhesive. This is better than nails because nails expand and contract as the outdoor temperature changes.

How to Repair or Replace Spring Bronze Weather Strip

How to Fix Rotted Areas at the Bottom of a Sash

If rotted areas on the bottom surface of the lower sash allow infiltration, repair these areas with epoxy wood filler.

STEPS

1. Buy a wood epoxy that is formulated for rotted windows.
2. Follow carefully the instructions on the label.
3. In addition to the instructions, it is best to make the bonds stronger than other places where wood epoxy is applied, because closing the sash could shake off the epoxy.
4. Make the bonds stronger by drilling many tiny holes onto the sash where the epoxy will be applied. This gives it much better adherence.

How to Fix Rotted Areas Between Glass and the Sash

If a sash is badly deteriorated and air leaks in between a pane of glass and the sash, remove the pane of glass and repair the rotted sash. The gap could be sealed with caulk, but the sash would continue to rot until it must be replaced. This work must be done on a day when it has not rained for one or two days. The sash should be very dry to paint, before putting the window back in.

TOOLS AND MATERIALS:

STEPS:

1) Cover the area under the window with a large drop cloth to catch tiny pieces of glass.sssssssssssss 

2) Remove the pane of glass by carefully chiseling out the window putty and pulling out the glaziers points. Use a sharp ½” wood chisel and a flexible 1″ putty knife. The pane is likely to break, so before starting, check if your local hardware store has glass in stock, and a person to cut the glass. sssssss sssss

3) Repair the rotted area using wood epoxy. See section directly above, “Fix Rotted areas at Bottom of Sash”.sssssssss 

4) Prime and paint the areas where the wood is bare. Paint one or two days after a rain, depending on the outdoor temperature, and allow the paint to dry before replacing the glass and applying the glazing putty. sssssssss 

5) Replace the pane of glass.

6) Push in two or three glazier’s points on each edge of the pane. Push them in with a chisel or a putty knife, being careful not to crack the glass.

7) Apply the glazing putty with a 1″ flexible putty knife. Carefully read the instructions on the container. 

8) Days later, paint the glazing putty. The time required to dry is given on the container. 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. 

How to Seal the Gap Above an Upper Sash by Fastening It to the Frame

If an upper sash which is never opened falls slightly, leaving a thin gap, fasten it into place with two screws and then caulk around its edges with clear indoor/outdoor caulk. This will prevent air from leaking through and also prevent the sash from slipping down.

STEPS:

1) Buy two 2″ to 2½”trim screws. These have small heads which is more attractive.

2)  Put in the screws through the bottom surface of the sash, at 45° angles. The window jambs, which the sashes slide against, are ¾” thick and behind them are sash cords, so don’t use longer screws that could snag the sash cords.

How to Re-Attach the Bottom Rail of a Sash

STEPS:

1)  Buy two 6″x6″ flat corner braces and twelve 1″ screws. The screws in the packages are too short.  

2)  Push up the bottom rail and fasten it with the 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. 

3)  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.

How to Repair a Fallen Windowsill in a Very Old Home

If your home is very old, typically over 100 years old, some of the window sills may have fallen slightly to create a gap between the lower sash and the window sill. Very old wooden window sills normally have one piece inside the house and one piece outside the house. When the window is closed, the sash rests on the piece that is outside the house.

If this piece has fallen significantly and become separated from the other piece, leaving a gap below the sash, try to repair it. If left unrepaired it will fall farther. 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 to the left. In place of using 3″ finishing nails, you could screw in 2 1/4″ trim screws, or 2 1/2″ star bit screws with the smallest heads available. Star bit screws are strongest but you must buy them by the box and they are expensive, and buy a star bit.  

How to Seal a Small Gap Under the Lower Sash 

To seal the gap below a lower sash, use 1/8” thick ribbed profile EPDM weather strip (weatherseal). EPDM is a type of rubber designed for weather strip. It is very durable it and is elastic at sub-zero temperatures. 1/8” thick ribbed profile EPDM weather strip is the thinnest EPDM weather strip, it compresses to about 1/16″. It is self-adhesive, but copper weatherization nails should be used to add strength.

The surface must be above 40° F degrees and dry for adhesion. If the outdoor temperature is cold or 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. thumb latch no longer closes after putting in weather strip, mount the rear part of the thumb latch onto a wooden shim or about two pieces of cardboard to make it higher. Screw it back on using slightly longer screws. 

Caulk the Channel in the Top Rail of the Lower Sash

On the lower sash of a wooden double hung window, the top edge of the pane 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.

The “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.

weather strip can usually be easily replaced on modern double hung windows if you find matching weather strip. You simply remove the sash from the window opening, slide out the old weather strip 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.

How to Insulate a Window If Air Leaks Under the Sash Because the Sash is Crooked

If a sash is crooked, mount 1/4″ thick self-adhesive low density foam weather strip tape to the window sill where the weather strip on the sash rests on it. Low density foam weather strip 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.

How to Replace Damaged or Missing Weather Strip

If air leaks through above or below the sashes due to damaged or missing weather strip, try to order identical weather strip 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.

Weather strip on the top and bottom of a sash is normally vinyl, and normally “kerf-style”, that is, it is inserted in a kerf, a thin slot in the sash. If it is instead pile weather strip, ????? ,

Shown to the right are two shapes of kerf-style vinyl window weather strip used on the tops and bottoms of window sashes. Shown below is a vinyl sash with pile weather strip. 

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