Dehumidifiers: What To Look For

How dehumidifiers work

Humidity is typically defined in terms of relative humidity, which is the amount of water vapor present in the air compared with the greatest amount of water the air can hold at a given temperature. The optimal relative humidity indoors is 30 to 50 percent in the summer, and 30 to 40 percent in cool weather. Dehumidifiers can maintain the indoor relative humidity at the desired level, controlling musty odors and protecting furniture from water damage. While most dehumidifiers will function down to 41 degrees Fahrenheit, they are at their most efficient when temperatures exceed 65 degrees.

Dehumidifiers vary in the number of pints of water they can extract from the air in a 24-hour period. This capacity typically is in the range of 25 to 70 pints, but some units can remove more than 100 pints of water. For a large basement with 1,200 square feet, you'll need a 70-pint unit. A 50-pint unit may be sufficient for an 800-square-foot area. The Associates of Home Appliance Manufacturers (AHAM) warns, however, that climate, number of doors and windows, number of people, and activities in the space can influence the size of dehumidifier that's necessary to efficiently reduce the humidity.

Top dehumidifiers have an Energy Star label signifying they meet the energy-efficiency criteria set by the U.S. Environmental Protection Agency (EPA). These models remove the same amount of moisture as standard models while consuming 15 percent less energy. By looking at the list of certified dehumidifiers at the Energy Star website, you'll notice that larger-capacity models generally have higher efficiency ratings. For this reason, ConsumerReports.org says a capacity of 60-70 pints is preferably for someone who routinely needs to run a dehumidifier.  

Here are some other things experts say you should consider before buying a dehumidifier:

• Note the size of the collection container. Most dehumidifiers include a container for the condensed water. Unless you've hooked up a hose for continuous drainage, you'll need to empty the tank when it fills up and the unit automatically turns off. A larger container will need to be emptied less frequently than a smaller one.

• Digital display of the current humidity level. This helps you gauge how well the dehumidifier is working and how soon you can expect it to reach the target humidity level and turn off.

• Automatic restart after a power outage. This is a nice convenience if your power supply is unreliable.

• Automatic defrost for use in basements. If the temperature drops below 65 degrees Fahrenheit, the condenser coils can ice up and become more inefficient at removing moisture from the air.

• Indicator light showing it's time to clean the filter. Most dehumidifiers have a washable filter that needs to be cleaned about every 250 hours of operation. An indicator light that shows it's time to clean the filter is an added convenience.

• A timer for delayed start or stop. This feature allows you to control when the dehumidifier turns on or off. You can schedule it to only turn on at times of the day when you aren't around to hear it or during non-peak electricity rates.

• Make sure you have space. For optimal operation, dehumidifiers must be surrounded by good air circulation. For a unit with a top exhaust, you need 8 to 10 inches on all sides, so it shouldn't be placed flat against a wall. If you choose a dehumidifier that exhausts out the back, you'll need 12 inches or more.

How dehumidifiers work

Humidity is typically defined in terms of relative humidity, which is the amount of water vapor present in the air compared with the greatest amount of water the air can hold at a given temperature. The optimal relative humidity indoors is 30 to 50 percent in the summer, and 30 to 40 percent in cool weather. Dehumidifiers can maintain the indoor relative humidity at the desired level, controlling musty odors and protecting furniture from water damage. While most dehumidifiers will function down to 41 degrees Fahrenheit, they are at their most efficient when temperatures exceed 65 degrees.

Dehumidifiers vary in the number of pints of water they can extract from the air in a 24-hour period. This capacity typically is in the range of 25 to 70 pints, but some units can remove more than 100 pints of water. For a large basement with 1,200 square feet, you'll need a 70-pint unit. A 50-pint unit may be sufficient for an 800-square-foot area. The Associates of Home Appliance Manufacturers (AHAM) warns, however, that climate, number of doors and windows, number of people, and activities in the space can influence the size of dehumidifier that's necessary to efficiently reduce the humidity.

Top dehumidifiers have an Energy Star label signifying they meet the energy-efficiency criteria set by the U.S. Environmental Protection Agency (EPA). These models remove the same amount of moisture as standard models while consuming 15 percent less energy. By looking at the list of certified dehumidifiers at the Energy Star website, you'll notice that larger-capacity models generally have higher efficiency ratings. For this reason, ConsumerReports.org says a capacity of 60-70 pints is preferably for someone who routinely needs to run a dehumidifier.  

Here are some other things experts say you should consider before buying a dehumidifier:

• Note the size of the collection container. Most dehumidifiers include a container for the condensed water. Unless you've hooked up a hose for continuous drainage, you'll need to empty the tank when it fills up and the unit automatically turns off. A larger container will need to be emptied less frequently than a smaller one.

• Digital display of the current humidity level. This helps you gauge how well the dehumidifier is working and how soon you can expect it to reach the target humidity level and turn off.

• Automatic restart after a power outage. This is a nice convenience if your power supply is unreliable.

• Automatic defrost for use in basements. If the temperature drops below 65 degrees Fahrenheit, the condenser coils can ice up and become more inefficient at removing moisture from the air.

• Indicator light showing it's time to clean the filter. Most dehumidifiers have a washable filter that needs to be cleaned about every 250 hours of operation. An indicator light that shows it's time to clean the filter is an added convenience.

• A timer for delayed start or stop. This feature allows you to control when the dehumidifier turns on or off. You can schedule it to only turn on at times of the day when you aren't around to hear it or during non-peak electricity rates.

• Make sure you have space. For optimal operation, dehumidifiers must be surrounded by good air circulation. For a unit with a top exhaust, you need 8 to 10 inches on all sides, so it shouldn't be placed flat against a wall. If you choose a dehumidifier that exhausts out the back, you'll need 12 inches or more.