A dehumidifier is mechanically very similar to an air conditioner and can cost as much per minute to operate. Here are 16 pages on how to improve dehumidifier energy efficiency – how to buy, install and use whole house and stand alone dehumidifiers to use less electricity.
Residential Dehumidifier Basics
Should You Use a Dehumidifier?
How to Buy and Install Stand Alone Dehumidifiers for Improved Dehumidifier Energy Efficiency
Energy Tips for Stand Alone and Whole House Dehumidifiers
Residential Dehumidifier Basics
Conventional residential dehumidifiers, both “whole house” and “portable”, remove water using the refrigeration cycle. This technology is used by refrigerators and heat pumps, and dehumidifiers also consume much electricity. Air is drawn in and runs over cold coils, moisture collects on the coils and it drips into a collection pan.
Whole house dehumidifiers remove moisture by drawing in air through the HVAC ducts and returning it through the registers. The dehumidifier can work in conjunction with the air conditioner, but can also work independently when the air conditioner is not running. Most portable and whole house dehumidifiers are controlled by a humidistat, which detects the moisture in the air and turns the dehumidifier on and off to keep the moisture at the level selected.
The ability of a dehumidifier to remove water from the air is called it’s capacity, and is given in pints. This is the amount of water it could remove in one day if it ran continuously. The average amount of water that a dehumidifier removes from the air will be a fraction of this. A typical portable model has a capacity of 30 pints, but may remove an average 10 pints of water per day. Portable dehumidifiers are normally called “stand alone dehumidifiers”.
Whole house dehumidifiers normally cost between $1000 and $2000, which is high, but they last long and need few repairs. The smallest units draw about 7 amps when running and the largest units draw about 14 amps. You will need to hire an electrician to install a branch circuit for it. If your home has only 100 amps the electrician may tell you that you cannot install a new circuit. Most homes have 200 amps.
Conventional stand alone and portable dehumidifiers, which are designed to remove moisture from one room or a basement, also use the refrigeration cycle. They can be set up to drain into a floor drain, a sump (which has a sump pump), a utility sink or a basement shower, and in some cases through a hole in the wall see How to Buy and Install a Stand Alone Dehumidifier for Maximum Energy Savings. If you have no place for it to drain you can drain it into a 5 gallon bucket. Almost all models have a bucket or tray, allowing you to set them up either way, but these may need to be emptied every day.
Before buying a stand alone dehumidifier you must check if the nearby outlet is on a branch circuit that can allow the amperage it will use, or if there are other appliances putting a high demand on the circuit. The largest stand alone models have a capacity of about 70 pints and can be used to dehumidify an entire basement. These models draw about 6 or 7 amps. Most basement circuits allow 15 amps. An extension cord could be used to power the dehumidifier from a farther away outlet, but it must be oun outdoor extension cord and it must be 14 gage wire. The smallest stand alone dehumidifiers have a capacity of about 25 pints. They are suitable for a small bedroom or a large closet. They draw about 4 amps.
When a stand alone dehumidifier is used in a basement, it will dry the air in the basement, but if moisture is entering the home through the basement walls it will collect it before it can raise the humidity level on the floors above. To buy and install a stand alone dehumidifier, see How to Buy and Install a Stand Alone Dehumidifier for Maximum Energy Savings and Energy Tips for Stand Alone and Whole House Dehumidifiers.
“Desiccant dehumidifiers” and “thermoelectric dehumidifiers” use different technologies which use much less electricity, but they are only effective for small rooms. Desiccant dehumidifiers use a desiccant material such as silica, which absorbs moisture from the air. They dry the air by blowing it over this material. The material is dried by air flowing in the opposite direction. The air leaves the house carrying the moisture. A wheel cycles the desiccant material. When the desiccant is at the bottom of the wheel, air from inside the house blows through it to dry. When it is at the top, air blows through it to to carry out the moisture.
Desiccant dehumidifiers are more often used by industries than by homeowners. They are less energy efficient than conventional dehumidifiers, and they do not control the humidity well because their effectiveness depends on the outside temperature and humidity. They can only be used in very humid conditions.
Thermoelectric dehumidifiers, which are also called “petite dehumidifiers” or “Peltier dehumidifiers”, are very small dehumidifiers which also do not use the refrigeration cycle. They use “Peltier technology”, in which an electric current passes through metals to create heat. The air passes through the hot metals to have the moisture removed. They are much less expensive than other stand alone dehumidifiers, but only suitable for small rooms. They are used in small bedrooms to help the residents sleep more comfortably.
The phrase “relative humidity” is used interchangeably with humidity. Relative humidity is the percentage of water vapor that the air can hold at that temperature. For example, the relative humidity may be 100% in a bathroom while running a shower because the air there cannot hold any more water vapor at that temperature. at a higher temperature it could hold more water vapor.
Should You Use A Dehumidifier?
If you have whole house air conditioning or several window unit air conditioners, you can lower your air conditioning electric costs by using dehumidifiers because you can raise your home’s temperature slightly when using them. The comfort level will be the same at a slightly higher temperature if the air is less humid. This savings alone may not pay for the cost of using a dehumidifier, but there are other reasons to use one. These include: reducing allergy and asthma symptoms; improving sleep; make a humid basement more comfortable; protecting your home from mold damage; preventing musty smells; protecting belongings stored in your basement; and reducing the repairs to your air conditioner.
The homes built in recent decades need dehumidifiers more than older homes because newer homes have better vapor barriers, they have more weather stripping on their windows and doors, and they have other improvements designed to prevent infiltration. Also, if you are doing a thorough weatherization of your home, including sealing the gaps that allow infiltration, you may have greater need for a dehumidifier.
Signs that the humidity level in your home may be too high:
- Musty odor
- Increased allergy or asthma symptoms. Allergy symptoms can be triggered or increased by mold, bacteria, and dust mites. Asthma symptoms can be triggered by dust mites, which grow in high humidity.
- Mold stains on the ceiling and walls.
- Water dripping off of window panes on very cold days
- You have trouble sleeping because your skin feels clammy.
- You set the air conditioning temperature lower than necessary because you feel uncomfortable.
- Water from condensation drips from water pipes
Also, if the humidity level in your home is too high, the moisture may eventually damage structural wood, carpets and paint, especially at the bottom of basement walls. If water occasionally enters your basement during a storm, you could use a dehumidifier for days or weeks afterward to remove the excess moisture from your home.
If you use a stand alone unit in a basement storage room to help protect perishable items, you cannot assume that they will be protected, so the dehumidifier may be wasting electricity. Water vapor enters through the wall and under the door. To check if the humidifier is lowering the relative humidity in your storage room, mount a hygrometer in the room. If the humidity is higher in your storage room than outside of it, replace its door with louvered doors.
Very small dehumidifiers, such as 4 pint per day Peltier dehumidifiers, which are inexpensive to buy and inexpensive to operate, can be used to lower the humidity in small bedrooms. This may allow the persons sleeping there to sleep better, so the central air conditioning can be turned off at night. In a large master bedroom a conventional portable dehumidifier can be used, but these cost about as much to operate as a small window air conditioner, and the branch circuit it would use may not have enough extra capacity for it.
Small, portable dehumidifiers are useful in rooms that tend to be too hot, such as rooms with large windows with sun exposure. They remove some of the moisture to make the room more comfortable.
Stand alone dehumidifiers can be expensive to operate because they don’t last very long and they are not very repairable. Their replacement parts are normally not sold. Expect service problems within a few years. Whole house dehumidifiers offer complete replacement part lists and are relatively easy to repair.
All dehumidifiers are expensive to use, especially if you include their replacement costs, but before deciding whether to buy one, read Energy Tips for Stand Alone and Whole House Dehumidifiers.
It is very hard to estimate how much a stand alone dehumidifier would lower your air conditioning costs over its life, partly because you cannot estimate how many years it will last and they often don’t last very long.
Stand alone dehumidifiers control the basement humidity levels of some homes relatively well but in other homes they control it very little or not at all. This is because water leaks in through the basement walls in some homes, causing the relative humidity to be 100% most of the time whether or not there is a dehumidifier.
To estimate how much it would cost to run a stand alone unit in your basement, you can assume that if your basement is relatively dry the unit would run closer to 15% and if your walls leak during a rain, it would run most or all of the time. To roughly estimate this, buy an inexpensive hygrometer. If the relative humidity is near 100% after a rain, the walls leak.
If there would be no way to set it up a stand alone humidifier to drain, you can buy a model that shuts off automatically when the bucket or tray is full.
How to Buy and Install a Stand Alone Dehumidifier for Improved Dehumidifier Energy Efficiency
Before buying a stand alone dehumidifier, estimate the capacity you will need. If its capacity is too large it will waste electricity because it will cycle on and off too often, and electricity is used when it cycles on. Also, it will cost more to buy. It will probably have a larger bucket or tray, so if you drain it manually you will have to drain it less often, but it will be heavier.
The capacity you will need depends on the size of the room or area and its dampness. For example, you would need a much higher capacity unit in a basement with block walls which rain water leaks into. A rule of thumb is that it is best to use a 70-pint model in the basement, which may be the largest model available where you shop. A model this large should not be used anywhere else because basements are larger than any room and because the humidity there is often high.
The chart below, published by the Environmental Protection Agency, gives estimates of how many pints of water per day must be removed by a dehumidifier for different size areas under different degrees of dampness. The capacity of the dehumidifier you use should be 2 or 3 times greater than the amount of water that must be removed. For example, if the room is 1000 sq. ft. and moderately damp, the table shows that 14 pints of water per day must be removed. For this, a 25- or 30-pint dehumidifier would be most suitable. There are other factors, such as whether a window on the floor is left open and whether the house has much infiltration. The recommendation given with one brand is that you use a 60 or 70 pint unit for an open basement and a 25 or 30 pint unit for a single room.
SSSSSCAPACITY OF DEHUMIDIFIER REQUIRED IN PINTS/DAY
|500 sq. ft.||1000 sq. ft.||1500 sq. ft.||2000 sq. ft.||2500 sq. ft.|
|Moderately Damp (feels damp and musty odor when weather is humid)||10||14||18||22||26|
|Very Damp (always feels damp with musty odor; damp spots show on walls and floor)||12||17||22||27||32|
|Wet (feels and smells wet; walls or floors sweat, or seepage is present)||14||20||26||22||38|
|Extremely Wet (laundry drying, wet floor, high load conditions)||16||23||30||37||44|
Source: Association of Home Appliance Manufacturers (AHAM)
Before buying a stand alone model, check that the branch circuit it will use has enough spare electrical capacity. Stand alone dehumidifiers have power requirements ranging from about 400 watts (3.3 amps @120v) to about 750 watts (6.25 amps @ 120v). This is printed on the box or given in the Use and Care Manual. Your 120v outlets will all be for 15- or 20-amp branch circuits. This will be indicated on the circuit breaker by the number 15 or 20 (an electric dryer may have a 30-amp circuit, but the plug for a dehumidifier will not fit into its outlet).
If you have a fuse box, the fuses for the 120 volt circuits will be labelled as 15 amp or 20 amp, but this is not proof of a circuit’s capacity because an incorrect fuse may be installed. The capacity of a circuit can be determined by the gage of the wire entering the fuse box, 15 amp fuses are used for 14 gage wiring and 20 amp fuses are used for 12 gage wiring (12 gage is heavier than 14 gage). However, if the fuse is 15 amps and the wiring is 12 gage, it is possible that a section of the circuit is 14 gage, so assume that a 15 amp fuse is the correct fuse and it is a 15 amp circuit.
If the power requirement of a dehumidifier is listed only in watts, compute its requirement in amps by dividing the wattage value by 120v (wattage = amperage x voltage.) For example, if a dehumidifier uses 500 watts, it uses 4.17 amps. To determine if the outlet you want to use is on a circuit with enough spare capacity for the model you want to buy, turn off the circuit breaker for that outlet. The outlets and lights that lose their power are on that circuit. Add the wattages or amperages of all the appliances and lights that are at times plugged into those outlets. Basement outlets are occasionally on first or second floor branch circuits, so if a basement outlet is the only outlet or light in the basement on that circuit, check on the first and second floors.
- Buy a dehumidifier with a bucket or tray that is the right size for you. They range from about 35 pints (2.2 gal) to about 135 pints (8.4 gallons). A large one may be too heavy to carry. A bucket or tray that is too small will on some days fill twice a day, so there will probably be days when the dehumidifier shuts off because you didn’t empty it.
- Stand alone dehumidifiers designed for energy efficiency are often called, “low energy dehumidifiers”.
- Models that are ENERGY STAR qualified have the highest energy efficiencies. The energy efficiency of a dehumidifier is measured by its “energy factor”. This is the liters of water removed per kilowatt-hour of energy consumed (L/kWh). When the energy factors for all ENERGY STAR qualified dehumidifiers were published by the EPA, the results indicated that almost all ENERGY STAR models with capacities of 30 pints had energy factors close to 1.4, and almost all models with capacities of 70 pints had energy factors of close to 1.8. The energy factors of smaller capacity models can be roughly estimated from this. You can estimate the cost of using an ENERGY STAR qualified model better than other models because you know, approximately, its energy factor.
- If you are buying a model for the basement and there would be no way for it to drain, buy a model that shuts off automatically when the bucket or tray is full. Most, if not all models do this.
- If you are buying a model for the basement and there will be a way to set it up to drain, such as a floor drain to empty into, buy a model that allows for automatic draining. Most stand alone dehumidifiers allow you to hook a hose to them to drain automatically.
- A stand alone dehumidifier with a humidistat can save electricity because it cycles on and off to keep the air around it at the relative humidity you select. It may not be able to lower it to this level on many or even most days, but it will save electricity on other days. These dehumidifiers are labelled, ”with humidistat” or “with relative humidity control”.
- If you buy a model that does not have a humidistat, buy one with a timer. These models will shut off after a set number of hours. You may, for example, operate it 4 hours each day. To determine how many hours is best, buy a hygrometer and test the humidity with the humidistat set to run 4 hours per day, 6 hours per day, etc.
- If you must set the dehumidifier next to a wall, buy a model with a top-mounted air discharge, which most models have as an optional way of setting it up. Models that discharge from the sides run less efficiently when mounted next to a wall.
- If the dehumidifier will be in a location where the temperature can fall to below 65°, buy one that is rated for low temperatures. Frost can form on the condensing coils if the air temperature drops below about 65°, depending on the model, because the condensing coils are always cold. Frost will insulate the coils so they don’t transfer heat well, making the dehumidifier inefficient, so it runs too many hours per day.
You could also buy a model with an “anti-frost sensor”, which turns off the unit when the air temperature drops below a set temperature. Either of these would be a good choice if they are ENERGY STAR rated. If you use a dehumidifier in your basement which is not rated for low temperatures, turn it off if frost forms on the coils because it is wasting electricity.
- Large stand alone models are slightly noisy because they are similar to room air conditioners. If this would be a problem, buy a model with a relatively low noise level. The noise level in decibels is given on the box or in the Use and Care Manual.
- If a dehumidifier will be used in an open basement, the largest available model should probably be used. Home centers carry models as large as 70 pints, and this is popular for large open basements, but larger models can be ordered. The wattage requirements of 70 pint dehumidifiers are 6 or 7 amps, which is probably too high for the branch circuit you plan to use. Most of the branch circuits in your house, except in bathrooms and the kitchen, are probably 12-amp circuits, and one of these should not be used for a 70 pint dehumidifier.
However, it may not be expensive to hire an electrician to install a 20-amp circuit for a dehumidifier if the dehumidifier can be located close to the main electrical panel, or if the basement is unfinished, making it easy to run the cables.
Estimate the Electric Cost
Before buying a stand alone dehumidifier you could roughly estimate how much it will cost in electric use. In addition, a significant part of its cost will be its replacement cost because they don’t last too many years and they are not very repairable. A very rough estimate of one month’s electric cost for a typical home is computed below. Your costs may be much different because the amount of water absorbed from the air each day depends on the humidity outside, how often it rains (the relative humidity is 100% on rainy days), and the average outside temperature.
The estimate uses a 70 pint model, which can remove 70 pints/day, but for this calculation it will be assumed that it removes 32 pints/day, because the chart above, published by the Environmental Protection Agency, shows that 32 pints per day must be removed to maintain a comfortable humidity level. The calculation is for an ENERGY STAR qualified model, the electric rate is $.12/kWh, and the basement is “wet” (space feels and smells wet, walls or floor sweat, or seepage is present) An energy factor of 1.8 liters/kWh is used because this is typical for a 70 pint ENERGY STAR model.
(8.35 kWh/day) x (30 day/month) x ($.12/kWh) = $30.07/ month.
The calculation shows this dehumidifier would cost $30.07/month in a wet month, which would normally be one of the hottest months of the year.
Where to Install a Stand Alone Dehumidifier for Maximum Efficiency
- Dehumidifiers with top-mounted air discharge can be placed against a wall. If yours doesn’t have this feature as an option, it should be located away from walls and furniture, so that air can circulate freely around it, for greater efficiency. Your owner’s manual will give you this distance.
- Don’t install it near a major source of dust, dirt or sawdust (e.g., woodworking equipment). This could clog the coils and filter.
- If possible, don’t install it where the temperature can fall below about 65°. This temperature may be different for some models. The coils can become covered with frost at low temperatures, which will reduce their performance.
How to Install a Self-Draining Stand Alone Dehumidifier in a Basement
- To install a stand alone dehumidifier in a basement, first buy the correct extension cord if one must be used. It must be a 14/3 cord, which have the wire gage of a 15-amp circuit.
- If you have a utility sink, mount the dehumidifier on a table next to it or build a shelf that is higher than the sink, and run the drain hose to the sink. The water must flow downward because the units have no pumps. It must be on a perfectly level surface or the vibrations will cause it to slide off.
- If you have a sump (a round pit in the floor) with a sump pump, or a floor drain, set the dehumidifier close to it and run the drain hose to it. If it is not close someone could flatten the drain hose or trip on it.
- If your basement has no utility sink, sump or floor drain, you could install a sink pump. This is an enclosed pump designed to move waste water upwards to a large drain pipe. It is used to drain sinks, washing machines, and dehumidifiers.
- If it does not freeze where you live, you could build a shelf for the dehumidifier above ground level and let the water drain to your yard. Build the drain using PVC pipe and PVC elbows glued together using PVC primer and glue. These materials are available at hardware stores. Outside, the PVC pipe should be connected to a garden hose to drain it away, or fall onto a splash block if the ground slopes away from your house.
- If your basement has no utility sink, sump or floor drain, you may be able to build a sump with a sump pump. The dehumidifier drains into the sump, which is a small round pit, and a sump pump pumps out the water when the sump becomes about half full. This could be a do-it-yourself project if you watch a good instruction video.
Energy Tips for Stand Alone and Whole House Dehumidifiers
- Use a hygrometer to check the relative humidity in your home. They are inexpensive and designed to be attractive when hanging on a wall. They are sold at garden supply stores and home centers. If the hygrometer indicates that the relative humidity is below 50%, you are wasting electricity by running your dehumidifier too many hours per day. If you use a whole house dehumidifier, mount the hygrometer in the room you occupy most often.
- If you use a stand alone dehumidifier, or a whole house dehumidifier that is plugged into a wall outlet, use an electricity monitor to measure how much electricity is used each day. This will allow you to calculate how much it costs each day and decide which days or months to use it. You plug the dehumidifier into monitor and plug the monitor into the wall outlet. They are available for $20 to $30 in hardware stores and home centers.
- Open windows, especially basement windows, and use window fans. Basements are much more humid when the air cannot escape.
- Use a hygrometer to find the highest humidity that is comfortable for you, which may be higher than 50%. Set the humidity at this level to save electricity.
- Use a hygrometer to determine which months you should use the dehumidifier.
- If you use a stand alone dehumidifier to prevent mold growth in parts of your basement, try using fans to move the air away from those areas. Fans cost much less to operate than any dehumidifier. If air cannot circulate in a basement, the relative humidity could easily remain near 100%. The fans may not lower the relative humidity, so you should use a hygrometer to test their effectiveness.
- Take measures to lower the humidity in your home to minimize the use of the dehumidifier. Some of these measures could also prevent water from damaging your walls and prevent mold and termite damage:
- Connect plastic downspout extensions to your downspouts to prevent rain from penetrating the foundations and entering your basement. These are available at home centers and hardware stores for about $5, and no tools are required for installation.
- Keep your gutters and downspouts clear.
- If the soil slopes toward the foundation, water will collect next to your house after a heavy rain. Add top soil to change its grade.
- Install vent fans in your kitchen and bathrooms.
- If you dry your laundry on an indoor clothes rack, install an outdoor outdoor clothesline or clothes rack. This will prevent much water vapor from entering your home.
- If you have a crawl space with a bare earth floor, cover it to prevent water vapor from entering your home. Use 6-mil polyethylene sheeting, which is often sold in 10’ x 100’ rolls, in paint departments of home centers and in paint stores.
- If you use your whole house dehumidifier because one person in your home needs dryer air and they spend most of their time in the same room, buy a stand alone dehumidifier for that room and turn off the whole house dehumidifier.
- If you use a stand alone unit in your basement or if you use a whole house unit, keep the basement windows closed on rainy days. The outdoor relative humidity is approximately 100% on these days, so air that enters the house will bring in water vapor.
- Do the maintenance procedures given in your Use and Care Manual to keep it operating with maximum efficiency. If you don’t have it, try to read it on the manufacturer’s website. Typical recommended maintenance procedures include:
- Wash the filter if it is washable or replace it if it is not washable, once each year. If there is a removable front cover, there may also be a foam filter inside that should be cleaned.
- Clean the dust and debris from the coils. This will improve the unit’s efficiency and may increase its life. Dirt on the coils can become damp and freeze. This can make the coils so ineffective that the dehumidifier runs almost continuously and will greatly shorten its life.
- Do not place a stand alone unit close to a wall. They operate less efficiently if they are less than about 12″ away, depending on the model. Use and Care Manuals give the minimum distance the unit should be, and for some, this distance is 12”. If the unit has top-mounted air discharge, rather than side air discharge, it can be mounted next to a wall.
- If you have a stand alone dehumidifier that runs hours each day but the water bucket or tray is not filling up every one or two days, it needs to be repaired or replaced because it is wasting electricity. Check if the coils are clogged with debris or covered with dirt that has frozen. The other possible problems are probably not repairable.
- If you use a stand alone dehumidifier in your basement to reduce the humidity in the upper floors, mount a hygrometer on the first floor to check if the dehumidifier is effective. You may find that it has little or no effect and is only wasting electricity. They are sold at garden supply stores and home centers. You may choose to use your dehumidifier only in the summer, or replace it with a larger model.
- If your dehumidifier drains into a basement floor drain that drains very poorly, snake the drain to open it. When it is backed up, water evaporates into the house, raising the home’s relative humidity.
Whether you replace your dehumidifier with a low energy dehumidifier or you only use energy tips suggested above, you will soon be seeing lower electric bills from the improvements in your dehumidifier energy efficiency.