Dehumidifier - How to Choose

How to Choose A Dehumidifier

Dehumidifiers remove water from warm, humid air, working something like an air conditioner in that they move the warm air past two coils. Moisture from the air condenses on one set of coils much like an air conditioner’s evaporator coils. The water drips into a reservoir or through a hose to a drain. The other coil warms the air, which is blown into the house or room. Although a dehumidifier does not cool the air, it makes it more comfortable because it decreases the humidity. A dehumidifier does not function well under about 65 degrees.

Air conditioners dehumidify the air during the process of cooling it, so dehumidifiers are needed primarily where air conditioning isn’t available, such as in non-air-conditioned apartments or houses and uncooled or damp areas such as basements.

There are a number of specialized products available such as a home dehumidifier or a crawl space dehumidifier.

Dehumidifiers and how they work

Heat pump dehumidifiers

Dehumidifiers use a heat pump (similar to an air conditioner's heat pump) or chemical adsorbents to remove moisture from the air without cooling the air.

A heat pump dehumidifier uses a fan to draw indoor air over a heat exchange coil. The coil is almost freezing. The water in the air condenses on the coil and is drained. A second heat exchange coil reheats the air, which the dehumidifier exhausts into the room.

A heat pump dehumidifier dumps heat lost from the compressor and fan motors into the air. It returns to the indoor air the heat generated by the dehumidifier turning water vapour to liquid.

Chemical adsorbent dehumidifiers

This type of dehumidifier is designed for hot, humid climates and is not really suited for use in Canada.

Chemical adsorbent dehumidifiers absorb moisture from the air with a “desiccant”—a drying agent such as silica gel. The desiccant is on a heat exchange wheel. A separate air loop dries the wheel and exhausts the hot, damp air outdoors through special ducting.

A chemical adsorbent dehumidifier uses more energy than a heat pump dehumidifier. It is only cost-effective when it uses natural gas for heat exchange—and then only if natural gas is available at a low summer rate.

Homemade dehumidifier
Some inventive people use bags of road de-icing salt to absorb moisture from the air. The wet salt solution drips into a pan or floor drain, drying the air. Because the salt runs off with the water removed from the air, it must be replaced. The system has no moving parts.

Anyone who has poured a cold glass of iced tea on a hot, humid summer day knows that moisture will condense on the glass. When air cools, it loses its ability to hold moisture; in the case of the cold glass, the moisture in the air condenses right onto the glass. If the glass is left on a table long enough and if the air is very humid, a significant puddle of water can form. You may have noticed the same phenomenon in any air conditioner. The moisture in the air inside the room condenses onto the air conditioner's cold coils. If it's a window unit, the water drips out the back of the unit onto the ground.

A dehumidifier is simply an air conditioner that has both its hot and cold coils in the same box. A fan draws the room's air over the cold coil of the air conditioner to condense the moisture (which normally drips into a bucket). The dry air then passes through the hot coil to heat it back up to its original temperature. That's all there is to it!

HOW TO CHOOSE A DEHUMIDIFIER
Determine the square feet of the room & the conditions that exist in that space. The corresponding numbers in the table show the dehumidification required in pints per 24 hours.
Humidity Level*	AREA - SQUARE FEET
	500	1000	1500	2000	2500	3000	3500
	CAPACITY - PINTS PER 24 HOURS
MODERATELY DAMP-Space feels damp & has must odor only in humid weather	10	14	18	22	26	30	34
VERY DAMP- Space always feels damp & has musty odor. Damp spots show on walls or floors	12	17	22	27	32	37	42
WET- Space feels damp, smells wet. Wall or floor sweat or seepage is present	14	20	26	32	38	44	50
EXTREMELY WET- Laundry drying , wet floor, high load conditions.	16	23	30	37	44	51	58
*Dehumidification variables also include other factors such as climate, laundry equipment, number of doors & windows, number of area occupants, degree & intensity of area activity.

When you choose a dehumidifier, make sure you know:

The size you need for your house—most manufacturers have sizing charts.
Purchase cost.
The EF.
Whether you have to empty the condensate tub or the unit is self-draining. A self-draining dehumidifier is best, because you don't have to remember to empty the tub every day.
Whether it has an automatic defrost feature—it should have one.
The noise level at low and high speed.

Dehumidifier EF 1.2 1.8
Days used a year 80 80
Litres removed a day 20 L 20 L
Electrical cost per year $107 $71
Annual savings $36

The manufacturer's reputation for quality and guarantees.
The service available from the seller or a local service depot.

Maintenance and operating tips
Clean the internal filters frequently. Start by cleaning them every two weeks. If the filters are not very dirty you can clean them less often.

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

You can't set and forget the controls on a dehumidifier. In the muggy days of summer, 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 doesn’t solve the problem
A dehumidifier alone may not solve severe moisture problems in your house. Your first course of action is to find the moisture source. Take steps to reduce the amount coming into your house—or to stop it completely. Remember: a dehumidifier is useful— but it isn't magic.

Although this information product reflects housing experts’ current knowledge, it is provided for general information purposes only. Any reliance or action taken based on the information, materials and techniques described are the responsibility of the user. Readers are advised to consult appropriate professional resources to determine what is safe and suitable in their particular case. Canada Mortgage and Housing Corporation assumes no responsibility for any consequence arising from use of the information, materials and techniques described.

Also, if you are planning to use your dehumidifier in a basement, consider a pump model over a non-pump one. While a pump model may be more expensive, it is capable of emptying its tank by itself, saving you the trouble of running up and down the stairs carrying heavy tanks full of water and assures you the piece of mind while you're away from home.

Air Purifier:

Air Conditioner: