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Buying Guides - Dehumidifiers

What is a dehumidifier?

A dehumidifier is an effective way of preventing moisture problems by removing excess water vapour from the air in a home environment. It does this by drawing indoor air over a heat exchange coil. The coil is cooled (similar to an air conditioner's coils) and water in the air condenses on the coil and is drained. A second coil reheats the air, which the dehumidifier returns into the room.

Why do you need a dehumidifier?

Moist air in a home can be a problem. Too much moisture can cause condensation on windows, can lead to damage of materials especially wood, promote the growth of mold and can even cause itchy skin and nasal passages. Indeed, molds can cause allergic reactions and make breathing difficult for some asthmatics.

Moisture problems are most evident in basements. This is because as air is cooled it cannot hold as much moisture. And because basements, especially their surfaces like floors and walls, are cooler, you get condensation. A dehumidifier will take away that cold and clammy feeling evident in most basements and get rid of the dampness odour.

Even homes equipped with air conditioners often need dehumidifiers to remove the excess moisture that the air conditioner cannot access such as in a basement. Use of a dehumidifier in combination with an air conditioner can help reduce the load on the air conditioner by removing the heat retaining excess moisture.

What is the right moisture level?

A relative humidity level indoors of less than 50% relative humidity (RH) is generally seen as the ‘normal’ level. There may be instances in cold weather where a level as low as 30% RH is preferred if condensation appears on windows. Some asthmatics may consider keeping the humidity level at 40% RH or less.

What do dehumidifers cost?

Like many other appliances, dehumidifiers vary in price. The amount you spend on a dehumidifier will depend on the model you choose and the capacity and specific features it offers.

Purchasing tips - choosing the right capacity model

Dehumidifiers are available in different capacities and are rated in litres or U.S. Pints of water removed in a 24 hour period (at standard conditions). The easiest way to select the right capacity dehumidifier for your application is to use a dehumidifier selection guide:

Dehumidifiers selection guide

Consider these important dehumidifer features...


A dehumidifier’s performance is measured in the amount of moisture it extracts from the air. In general, the higher the output, the faster a dehumidifier will remove water from the air and the larger a space it can dehumidify. Models typically range in capacity from 15 all the way up to 65 U.S. pints.


Dehumidifiers that are Energy Star qualified are the most efficient models in their rating categories. Energy Star qualified models have lower operating costs for each litre of water removed versus the amount of electricity consumed. Selecting an Energy Star labeled dehumidifier can save you dollars in energy costs.


Manual, rotary knob, controls are the simplest to operate. Automatic humidistats offer the convenience of selecting, and automatically maintaining, a desired comfort level. Fan speed control provides the ability to operate at a quieter setting. Advanced electronic controls include many additional features such as readouts of room environment and operating settings, audible alarm, pause, and automatic fan speed control.

Low temperature operation

Most dehumidifiers come equipped with an automatic defrost. If the room is too cool, a dehumidifier can frost over and stop removing moisture. Automatic defrost will melt this build up so that moisture can again be collected. For much colder environments, some electronic models come with ‘Low Temperature Operation’ which will further extend the effective operating temperature of a dehumidifier.

Product maintenance and operating tips

Clean the filters frequently. Vacuum the coils every spring and fall if they get dirty.

On muggy summer days set the controls to remove more moisture. Lower the setting to remove less moisture in spring, fall and on clear dry summer days.

When a dehumidifier is first installed, it will take a lot of water out of the air. But after a week or so, the amount removed will drop as the ‘extra' moisture has been taken out.

Cooler air holds less moisture, thus much less dehumidification occurs at temperatures below 15°C (60°F). Much less, or no moisture, will be collected even if the humidistat is set at its maximum. This does not indicate any fault on the part of the dehumidifier but rather that the relative humidity and temperature conditions are below where a dehumidifier should be operated. Continually running a dehumidifier in this situation only wastes energy without deriving benefit. Below 30% relative humidity there is very little moisture in the air and further attempt at dehumidification is detrimental to the home environment and its occupants.

Placing a dehumidifier

If the aim is to dehumidify the whole home, and you have forced air-heating and central cooling, then it doesn’t really matter where you place the dehumidifier. If you do not, and a specific area needs to be dehumidified, such as a laundry room, then place the dehumidifier as conveniently as possible in or near that space.

When a dehumidifier doesn't solve the problem

Sometimes severe moisture problems exist which cannot be entirely rectified through the use of a dehumidifier. In such cases you will need to find the source of moisture and take steps to reduce the amount coming into your house. It is best to consult with a building expert in these situations.

Catastrophes, such as plumbing leaks or floods, can cause serious problems and will need emergency repairs to deal with them. Once solved a dehumidifier can quickly dry things up again.

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