Choosing a Dehumidifier

By: Rob Parker, RHI, CHI, CMI

The hot and hazy days of summer tend to increase the amount of humidity present inside your home. Humidity is the amount of water vapour in the air and measuring the relative humidity (RH)  is an important first step in deciding if you need a dehumidifier.   An instrument called a “hygrometer” can be used to determine the percentage of moisture in the air relative to the maximum amount the air can hold at that temperature. If the relative humidity reads above 50 per cent, running a dehumidifier can take away the excess moisture.

If you have a humidifier on your furnace, make sure the unit and water to the unit is shut off in the summer. By leaving the humidifier on, you are contributing to the amount of humidity in the air and making your air-conditioner/and or dehumidifier (if one is used), work harder.

For houses with no air conditioning, a basement dehumidifier can usually keep basement RH lower preventing moisture and comfort problems. Running the furnace fan on a low speed may help to circulate the cooler air from the basement to other parts of the house. This is also dependent on whether or not a cold air return duct is present in the basement. If you have leaks through your basement or crawl space walls and floors or your basement is damp, then you have to correct the moisture problem first.

A dehumidifier can be an important appliance for a healthy home and should be chosen with care. CMHC (Canada Mortgage and Housing Corporation) offers the following tips on the choice and use of dehumidifiers:

• The unit that you choose should meet all of your needs, not just a minimum purchase price that leads to more expenses in the long run. Choose a seller who can answer most of these questions for you, then go on line to get the rest of your questions answered.
• If your house has a forced-air furnace you can place your dehumidifier in any room or space that is heated or cooled by the furnace ducting. The forced air system will circulate air to and from the dehumidifier to help control humidity throughout the house. However if you have a room or basement with a moisture problem, it is usually more effective to locate your dehumidifier there. If you use radiators for heating, you should place the dehumidifier in the room or space with the highest relative humidity levels; something that can be determined by moving a calibrated hygrometer around your house.
• If at all possible, drain the dehumidifier to a sump pit or floor drain, so that you do not have to empty the tank. A full tank shuts off the dehumidifier and when this happens, it is not doing its essential job. A connection can be made into the drain serving a nearby sink or tub so that connecting the dehumidifier to drainage is simple and permanent. This connection should be above the P trap in the drain, to prevent exposure to sewer gases.
• Placing the dehumidifier on a strong shelf makes drainage easier and allows you to easily see the controls, if the height is right. Take measures to prevent the dehumidifier from falling from the shelf as the units vibrate when operating. The laundry or utility room is the most common location for dehumidifiers, but if your utility room gets quite cool in wintertime, be sure that the dehumidifier model that you choose is rated for cooler conditions.
• Modern dehumidifiers require and allow little consumer maintenance other than keeping the air filter clean and checking that the settings are what you want them to be. Since a dirty air filter can dramatically increase operating costs and reduce moisture removal rates, the filter should be checked once a month. The filter check and cleaning should only take a minute or so.
• Choose a unit that has a long warranty period (five years is common) and be sure to send in the warranty card or register your new unit online. Note: Do this promptly as there is often a maximum length of time allowed for sending in the warranty paperwork after the date of purchase. Your dehumidifier paperwork will include all of that information. Save the paperwork in a safe place after you read it carefully, as you may need it in the future.
• Dehumidifiers are usually sized by floor area and the level of dampness of your home. Natural Resources Canada has published a chart to help you determine the size of humidifier you need for your home. This information can be found on their website at:

http://oee.nrcan.gc.ca/residential/business/manufacturers/appliance.cfm?attr=4#dehumidifiers

The purchase price of your dehumidifier is only one of the many costs that you should consider when buying a unit for your house. For instance, the operating costs associated with the electricity consumed by dehumidifiers over the life of the unit can be the same as, or more expensive than, the purchase price. With the rising cost of electricity, operating costs are important to consider when making your decision; however, if you do not get excessive indoor moisture under control, the costs of resulting damage and adverse health effects can be much higher than the costs of dehumidification.