Energy efficient dehumidifiers

Tips for cutting humidity without breaking the bank

Most people looking for energy efficient dehumidifiers could use a basic understanding of causes and prevention of humidity before they go shopping for the best dehumidifier. Just looking at the ENERGY STAR ratings of energy efficient dehumidifiers and buying the highest rated one isn’t enough.

You need to understand where humidity comes from, how to prevent it in the first place, and how dehumidifiers are rated, before you go choosing the best solution for your house.

Where does it all come from?

It doesn’t seem to matter how much you invest in waterproofing your house. Unless you live in a desert, chances are there’s some humidity in your basement. Where does it come from?

Humidity can be naturally present in the air that circulates into your house from outside. If you have doors or windows open, for instance in spring or summer, or if you have a lot of air leakage through walls, floors, ceilings, windows and doors, humid air enters your house. If you have air being exhausted from your house, the exhausted air has to be replaced with air from the outside somehow. For example, if you burn a wood fire, the oxygen to feed the fire is probably coming from inside your house, and that draws cold, potentially humid air inside from gaps in the shell of your house.

Basements tend to be cooler than the rest of the house, or indeed than the outside air during warmer months. The cool basement walls cause that humidity to condense out of the air, leading to problems with mold and mildew.

So one way you can cut down on moisture is to reduce the amount of fresh air coming into your house, especially during humid weather.

Water can also seep through basement walls from outside your house. There are four angles of attack for reducing this seepage: directing surface water away, sealing the outside of the basement walls, sealing the inside surface, and improving drainage below your foundation. More on those points later.

A third source of moisture, particularly when the house is sealed up during winter, is all the water vapor produced by human activities such as breathing, showering, drying laundry indoors, and cooking. This can add up to as much as 80 liters or 20 gallons a day in an average house.

Best energy efficient dehumidifiers

The most energy efficient dehumidifier is one that never needs to be turned on. In other words, as much as possible, solve the humidity problem instead of dealing with the symptoms. This is one of the golden rules of energy conservation in general: reduce demand for the task at hand. If you can make your basement dryer through renovation projects, or changing some household practices, or by buying a more energy efficient alternative such as an energy efficient air exchanger to prevent humidity from building up, you won’t need a dehumidifier as much, or even at all. So let’s start with prevention ideas.

We’ll cover keeping surface water out, keeping ground water out, and reducing moisture production in the home, in the next three sections. But if you already know all about this, and have done everything possible to get rid of moisture problems to start with, skip to my primer on energy efficient dehumidifiers below.

Keeping surface water out

Water pooling in your driveway, or pouring out of your or your neighbor’s eaves troughs, or gushing out the downspouts at ground level, wants to find its way downhill. And if there’s soil or sand or gravel around your house, or a crack between the pavement and the house masonry, the water will flow down through that substrate or crack until it can flow down no further, for example, when it reaches the water table. If it can’t flow straight down, it will start to flow across, which is when it will hit your basement walls in a big way and start working its way through. (Some of it will work its way through even if the rest can flow straight down, but if the downward path is blocked then the only place for it to go is through your walls!)

The first angle of attack is to keep the surface water from collecting around the walls of your house.

Eaves troughs and downspouts: Make sure all your eaves troughs and downspouts are in good working order. That gusher coming over the side of the upstairs eaves trough and cascading to the corner of your house is sending water down towards your foundation. Not only will this moisture weaken the masonry of your foundation but some of it will work its way into your basement. So make sure your eaves troughs are properly angled, are not falling off, are properly capped at the ends, and are not choked up with fallen leaves. If your neighbor’s eaves troughs are overflowing and spilling water onto your foundation, ask them to please get the problem fixed for their sake as well as yours.

Ideally, you should disconnect your downspouts from the city sewers, and instead divert the downspout water far from the house foundation so it can drain into the ground away from the house. There are good reasons to do this both to reduce basement humidity, and to reduce your impact on the environment. From your basement’s perspective, there’s a possibility that the drain pipe leading down from where the downspout enters the ground, has cracks or holes in it; water pouring down it during a rainstorm may be escaping from the sewage lines and entering the soil near your house. From an environmental perspective, in some cities with older sewage systems (such as my home town of Toronto), many eaves trough downspouts drain into the sanitary sewers instead of the storm sewers, which can result in sewage treatment plants overflowing into rivers and lakes during rainstorms.

Even better than simply disconnecting your downspouts, install a rain barrel so you can use at least a barrelful of water after each rainfall for watering or driveway scrubbing. But make sure the rain barrel overflow (which can be very fast during a downpour) does drain properly away from the house.

Driveways: Ideally, your driveway slopes away from your house rather than towards it. If your driveway runs alongside your house, it should slope away both towards the front or back, and towards the side farthest from your house. If you have a mutual driveway like mine (shared between two neighbors) the driveway should be both sloped towards the street, and sloped from the edges to the center, so that water doesn’t pool against your or your neighbor’s walls.

If there is a narrow gap of soil between your driveway and your house walls, you can prevent water from seeping into the gap by mixing mortar, and creating a sealing edge by running a line of mortar slightly off the vertical between the gap and the wall.

Finally, if your area gets a lot of snow in the winter, watch for snow build-up in or at the ends of your driveway. During a thaw, you don’t want snow at one end of the driveway to block meltwater from flowing away from your house. If it can’t escape along the driveway, it will work its way down through the substrate toward the basement walls.

Other areas around the exterior: Make sure that gardens, lawns, and other surfaces slope away from your home so water drains away instead of flowing down against the below-ground portion of your walls. Make sure, if you have a sump pump, that that drains well away from the house as well.

Keeping groundwater out

Here there are three options: seal your walls from the inside, seal your walls and floor from the outside, and improve drainage along outside walls and beneath your foundation. Which option you choose depends on factors such as your budget and whether digging outside, or renovating inside, are feasible.

Sealing outside walls: Seal the outside of your basement walls by hiring a waterproofing contractor to dig down to your foundation from outside, and apply a waterproofing compound to the exterior below-ground masonry. They can also fill the dug-out area back in with a combination of gravel and sand to improve drainage. While they’re at it, assuming they can get down below the footings, they can install drainage tile to draw the water table down below the floor of your basement. Just make sure they install the drainage tile to drain into the storm sewers. Drainage tile is not much good if it doesn’t connect to a drain!

Sealing inside walls and floor: If you have exposed masonry in your basement, or are planning to redo drywall (for instance, if the current drywall is covered in mildew and you’re going to gut and re-drywall), you can scrub down the masonry to a hard surface (removing any loose grit or mineral sweat from the walls), and use a parging compound (a thin, waterproof mortar slurry) to improve the waterproofing on the inside of your walls.

If you have concrete basement floors (with no flooring on top) check for cracks or missing concrete in the floor, and patch as needed. Humidity can seep in through cracks and exposed sand.

Drainage under foundation footings: If you are lowering your basement, for example by underpinning or benching it, make sure part of the plan involves installing drainage tile below the footings, and a sump pit and sump pump for the water to collect in and be drained from. In fact, your city permit office may require this to be in the plans as a condition of granting your permit.

Reducing moisture production in the home

Moisture you can prevent from being released into the enclosed space within your home will help cut down on basement humidity problems. While breathing isn’t something you can easily avoid, there are cooking practices that can make a difference, for example cooking with pot lids on where possible, and always running the range hood fan when cooking anything that produces significant amounts of steam. Keep showers short and not too hot, and run the bathroom fan while showering. Dry laundry on an outside lawn or rack rather than a basement line or rack if this is contributing to your humidity problem.

Make sure dryer vents in your basement are properly connected (for gas dryers, this is a safety issue as well as a humidity one); if you have an electric dryer and you use a dryer exhaust pipe with a heat recapture filter that allows some of the dryer heat to escape into the room for winter heat recycling, make sure you turn it off during the summer or at any time when humidity is a problem.

Fish aquariums can also be a source of humidity. It’s pretty easy to tell how much water they release into the air. Just look at how much water you have to add to them every week. If they’re well covered they shouldn’t play a major role in your humidity problem.

Remember that while there are definite health benefits to growing plants inside your home, indoor plants release plenty of moisture. The more you water them, the more water they release. Go for cacti and epiphytes, or keep your plant collection under control!

Use your intuition: If you think a bit about likely sources of moisture production within your home, you should be able to figure out ways to reduce moisture production.

Take out the humidity but not the heat

If you have humidity problems in the winter it may be that your home is sealed too tight. This is certainly the case with my parents’ cottage, an R2000 home with almost no air leakage to the outside. (R2000 was a Canadian energy efficiency standard relating to highly energy efficient homes. Unfortunately many homes built to this standard are so well sealed that moisture can’t escape in cold weather. The new standards account for the importance of proper ventilation of well-sealed homes.)

Well-sealed homes are a great way to save on heating and cooling costs, but a house can be too well sealed. That’s why my mother has to wipe the condensation off all the windows twice a day with a rag, and has to air the place out by opening both the first and second storey windows several times a day, and running the ceiling fans on high. Try doing that at -20C! Not great for your home heating bill.

While a well sealed home can be good for saving money on heating (as long as you don’t try the window-flush), it does cause humidity build up and can also cause adverse health effects, as inadequate ventilation can lead to a buildup of toxic off-gassing from plastics, foams, paints, even wood. Consider calling an HVAC specialist to have an appropriate capacity heat exchanger priced and installed.

Heat exchangers allow air to flow between the inside of your house, where humidity is typically in the 30%-40% range, and the outside, where on cold, crisp days it can be much lower. Most of the heat from your house is recycled back into the house, but the humidity is expelled along with the stale air. This is not only more energy efficient than using a dehumidifier, but better for your health. You get fresh, warm, dry air and the heat, and cold, each stay where you want them to stay!

The HE-100 Air to Air Heat Exchanger from Suncourt produces 100 cubic feet per minute (CFM) of air exchange between indoors and outdoors, and is suitable for a home of up to 2,000 square feet. (They also make a 150-CFM model for larger homes.) 70 to 80% of the heat is recovered in a typical installation. Note that these heat exchangers work for both indoor heated air and indoor air-conditioned air.

Energy efficient dehumidifiers primer

Let’s cover how humidifiers work, their capacity rankings, how energy efficient dehumidifiers are rated, and how to choose the best one for your situation.

Dehumidifiers remove moisture from the air using a compressor, condenser coils, and fan. Essentially a dehumidifier works like a miniature refrigerator, except that the purpose of the cooling cycle is to condense water out of the humid air, rather than to keep food cool.

Dehumidifiers usually continue running until the moisture reaches a set lower threshold, or until the tank is full (whichever comes first). I very much doubt anyone makes a dehumidifier that keeps on running after the tank fills up, as this would just keep reintroducing the humidity into the room in the form of a soaked floor or rug!

Another type of low-capacity dehumidifier uses silica gel technology to absorb moisture, and once the gel is saturated, you move the dehumidifier to a dry area and heat it to remove the moisture. See the bottom of this page for more on silica gel based dehumidifiers. While they are not suitable for dehumidifying a basement or a room, they are great for smaller confined spaces, such as a sealed bin where you want to keep something dry for long term storage.

Extraction and capacity rankings

There are two capacity rankings for a dehumidifier: extraction capacity, and tank capacity.

Extraction capacity is measured in liters or pints per 24 hours. All dehumidifiers sold in a country or ranked on a website are typically ranked by the same extraction capacity measurement. This measurement tells you how much water the dehumidifier can draw out of the air in a 24 hour period.

Tank capacity refers to how much water the tank can hold. Bear in mind that once your tank is full, it will not extract any moisture until you empty it. If you have a floor drain accessible near where you plan to place the dehumidifier, you may be able to attach a hose to the tank and run it to the drain, so that you never have to empty the tank. This is especially useful for basements in summer when you’re away on vacation or staying at the cottage for weeks on end. So make sure your tank comes with the appropriate fitting (most do). If running a hose isn’t an option, for instance because you plan to move the dehumidifier around or because there’s no accessible floor drain, make sure the tank capacity you look for is in keeping with how humid your basement is and how often you’ll be around to empty the tank.

Energy factor rankings

For energy efficient dehumidifiers, you need to look at the energy factor, which is the number of liters of water removed from the air per kilowatt hour (kWh) of electricity used. The higher the energy factor value, the more efficient the dehumidifier is.

This is different from the efficiency factor for many other appliances. A refrigerator for example lists its efficiency factor as the number of kWh per month or year of use, so the lower the number the better. In the case of an energy efficient dehumidifier, the more water it extracts per kWh the better, so the higher numbers are better.

The ENERGY STAR website lists dehumidifiers whose energy factor ranges from 3.56 (the best) to 1.2 (the worst) with a median rating of 1.62. Only two manufacturers, Therma-Stor Products and Munters Corporation, make dehumidifiers with a factor of more than 2.2. Therma-Stor manufactures all but one of these (the one labeled ‘Munters’); the brands the Therma-Stor products are sold under include Ultra-Aire (the most efficient of all at 3.56), Honeywell, Basement Systems, and Santa Fe. Note that the fact that Therma-Stor makes energy efficient dehumidifiers for other brands, does not imply that all the dehumidifiers sold under these other brand names are energy efficient.

Dehumidifiers rated by the Canadian Office of Energy Efficiency have Energy Factor ratings between 2.02 (best — only one model, the Bionaire BDQ25-UC) and 1.00 (worst — a number of brands, probably the same manufacturer, all models containing ’40’ in their model number, referring to a 40-pint capacity dehumidifier). EnerGuide energy efficiency cards are not provided on dehumidifiers sold in Canada, so read the Energy Factor rating carefully on the product spec sheet or packaging.

Don’t be misled by an ENERGY STAR label

Bear in mind that an ENERGY STAR rating on a dehumidifier does not mean it is really energy efficient, just more energy efficient than some of the others in its category. For example, in Canada, the OEE lists ENERGY STAR-rated dehumidifiers with an energy factor as low as 1.2, when the best energy factor is 2.02 and the worst is 1.0. This is because ENERGY STAR certification for dehumidifiers separates dehumidifiers into different capacities and provides certification for the better energy factors in each category. Thus the smallest-capacity dehumidifiers (under 25 pints per day) get an ENERGY STAR rating if their energy factor is at least 1.2 liters per kWh, while higher capacity dehumidifiers have higher thresholds. For residential dehumidifiers these thresholds are:

Pints/day	Liters/day	Energy factor (L/kWh)
≤25	≤12	1.2
>25 to ≤35	>12 to ≤17	1.4
>35 to ≤45	>17 to ≤21	1.5
>45 to ≤54	>21 to ≤26	1.6

Imagine you’re choosing between two dehumidifiers. One has a capacity of 24 pints a day, another 26 pints a day. The first is ENERGY STAR rated, and the second not. But guess what? The first, ENERGY STAR-rated dehumidifier might have an energy factor of 1.2, and the second, more energy efficient dehumidifier, might have a rating of 1.39 (more efficient). But because their capacities span a capacity threshold, the more efficient one fails to get the ENERGY STAR ranking.

Choosing the right extraction capacity

Always buy a dehumidifier that has at least the extraction capacity you need. To calculate capacity, first assess the level of dampness in your home. You will typically not require a pints-per-day rating greater than 25 unless your basement is extremely wet and at least 1,200 square feet in area, wet and at least 1,500 square feet, or usually damp and musty (but not wet) with at least 1,800 square feet. See the Dehumidifier Basics page (capacity section) on the ENERGY STAR website for a table that shows what capacity to use. But remember, higher capacity machines with an ENERGY STAR rating are typically more energy efficient than lower-capacity machines with the ENERGY STAR rating. So it will probably make sense to buy a higher-capacity machine, even if your humidity problem is not that great, in order to benefit from the higher energy efficiency ratings of more powerful dehumidifiers.

Relative humidity: what it means, what you should target

The objective of using a dehumidifier is to lower the ‘relative humidity’ of the air. Relative humidity or RH is a measurement of how close the air is to saturation with water vapor. At 100% relative humidity, water begins to fall from the air naturally.

This is the same as the humidity index given for predicting rain. A relative humidity of 100% outside means there’s so much moisture in the air that some of it has to fall out as rain.

For a house the objective should be to keep the relative humidity between 30% and 50% (warmer weather) to prevent bacterial growth, or between 30 and 40% (cooler weather) to prevent frost or condensation buildup on windows.

Go for a digital dehumidifier if you can

Digital dehumidifiers are ones with a built in humidistat, which measures the relative humidity or RH. There are typically two numbers displayed: current relative humidity, and desired relative humidity.

Analog dehumidifiers may simply have a dial indicating operating modes (‘low’, ‘medium’, ‘high’) or RH levels, but these are not as accurate as the digital models, and may not provide a consistent level of RH.

Use a hygrometer (humidity meter) to measure the RH in your home, and to determine whether your dehumidifier is set properly for the target humidity level. You can buy them from your hardware store or building center, or click on either of the models above to purchase one online.

Extra-cold basement? Get the right dehumidifier for the job.

If your basement is cool (below 65 degrees during at least part of the ‘dehumidifying’ season), make sure you get a dehumidifier model that can withstand lower temperatures. Otherwise, the cold basement will cause frost buildup on the coils, which will make them less efficient and may cause rapid on-and-off cycling of the motor. Ideally you’re looking for a dehumidifier with an auto defrost cycle.

If you hear this behavior, turn the dehumidifier off until the ice has melted and fallen away. If the behavior persists you may need to switch to a unit designed for cooler temperatures. For example, the Frigidaire low temperature dehumidifier shown at right (ENERGY STAR rated, 50 pints) can operate in temperatures as low as 42F.

Cutting energy costs, with whatever dehumidifier you use

If your basement is damp, and you’re running the dehumidifier, keep the doors to the basement closed. Leaving them open can allow moist air from above to circulate in the basement and create additional work for the dehumidifier.

Humid air on the main floor or outside won’t feel as damp as air at the same humidity level does in the basement, because the warmer air is, the more humidity it can carry. When that humid air goes into your basement, the cooler temperature of the basement floor and below-ground walls will increase the relative humidity of the air, as the air cools.

Keep your dehumidifier coils and fan clean. Don’t let dust build up around it. If you are doing woodworking, sanding, or other dust-producing activities, turn off the dehumidifier and cover it up until the dust has settled and been cleaned up. Otherwise your dehumidifier will be working much harder to perform the same amount of dehumidifying. When vacuuming your basement, or at least once a month during the operating season for the dehumidifier, vacuum the coils. Some dehumidifiers include a washable air filter you can clean to remove dust build-up; this filter prevents the dust from reaching the coils.

Use a timer for time-of-use electricity billing

You can save money on a dehumidifier that includes a timer, if your electricity rate varies by time of day. Set the dehumidifier to go on at night and go off during the day. Since summer is the most common time to run a dehumidifier, and daytime is the high-energy-use period of the day in summer (because of greater air conditioning loads), having the dehumidifier off during the day lowers the peak load on the system, which is good for the planet (because the lower peak load is, the fewer coal fired power plants we need to meet peak demand), and is cheaper for you if you pay higher rates for peak demand periods.

Finally, the essentials

In case you skipped to the bottom and just want to know the essentials of what to look for once you’ve already in the market for energy efficient dehumidifiers, here they are:

• Buy an ENERGY STAR qualified unit, but be aware that because of the way ENERGY STAR ratings are assigned, some dehumidifiers without such a rating may be more efficient than others that are ENERGY STAR certified
• Non-qualified units can use as much energy as a refrigerator. Know what you’re buying!
• Proper waterproofing of basements is of course your best bet, but use a dehumidifier if necessary, as the mould and mildew build up from not using one can cause dangerous mould spores which can lead to the development of allergies or even environmental illness in extreme cases
• ENERGY STAR models are more efficient on at least three counts than standard models: their refrigeration coils and compressors are more efficient, and their fans are too.

Most dehumidiier websites mistakenly equate ENERGY STAR certification with a guarantee of optimal efficiency. As I hope I’ve made clear here, ENERGY STAR certification refers to how efficient a dehumidifier is within a given capacity class, but higher capacity dehumidifiers are typically more efficient than lower capacity dehumidiiers. The key is to find a dehumidifier with at least the capacity you need, that has as high an energy factor as you can find (i.e. extracts the maximum amount of moisture per kwh).

What are mini-dehumidifiers?

You might be tempted to buy a mini dehumidifier, as people claim they are a cheap way to extract moisture without breaking the bank on the real McCoy. I mentioned this in the primer section above already, but in case you missed it: these are cute, very inexpensive units that use silica gel to absorb moisture, and then plug into a wall socket in a dry area to dry out the gel.

The energy factor on these units is atrocious compared to a regular dehumidifier, somewhere between 0.27 and 0.35 depending on the model, compared to an energy factor of 1.2 for the WORST regular dehumidifier. But you don’t use these (or at least you shouldn’t use these) where a regular dehumidifier would normally be used. Instead use them to keep moisture out of a confined space such as a storage box, or to remove humidity from the storage box after you have filled and sealed it.

For example, we made a trio of gingerbread townhouses a few years ago to display over Christmas. Every new year we pack them up in a big Rubbermaid container, place silica gel packets in the container, and tape it shut all around the edges. That way moisture can’t get in, and the silica gel packets absorb the moisture that was in the air when we packed it. The advantage of the Eva-dry over regular silica gel packets is that you can just plug it in to dry out the gel packets, but you can also use regular silica gel desiccant packets, and dry them out between uses by placing in a 250F (120C) oven for an hour or two. Not terribly energy efficient, unless of course the oven was on to begin with.