Whole-house fans draw cool outside air into homes through open windows and vent hot interior air out the attic, cooling the entire house.
ILLUSTRATION: ANIL RAO/RS MEANS
Whole-house fans are high-capacity fans mounted in a central hallway in the first-floor ceilings of single-story homes and in the top-floor ceilings of multiple-story houses. They draw cool outside air into a home through open windows. The air flows through the house and is vented out through the attic. Whole-house fans bring huge quantities of cooler, nighttime air into a home.
Whole-house fans are used in a variety of climates — from moderate ones where cooling demands are low, to desert areas with hot days and cool nights. They’re even helpful in hot, humid climates such as the southeastern United States, where they can be used in the spring and early fall, when cooling demands are lower.
Whole-house fans are typically run early in the morning and in the evening, when outside temperatures fall below indoor temperatures. You can also use them to cool your home during the day if you have a cool, dry, non-musty basement. Warm outside air is drawn in through basement windows, then is cooled as it passes through this naturally cool underground space. The air then flows up the basement stairs into the main living areas and is vented through the attic. Be sure there are no toxic fumes or radon in the basement, and that it is free of mold; otherwise, this can be an unhealthy strategy. And you don’t want to leave windows open in areas at risk for break-ins.
Be sure to cover and seal your whole-house fan during cold weather. The louvered opening can be a major source of heat loss during the winter. Moist air could also escape into the attic and condense, causing moisture or mold problems. You can install the fan cover on the attic side, or on the ceiling in the living space. You also can buy or make a cover out of fiberglass duct board and duct tape.
Installing a whole-house fan is a difficult project involving electrical work and carpentry. If you tackle the job yourself, be sure to follow the manufacturer’s instructions. You’ll find installation guidelines in many home repair books as well.
Because whole-house fans operate only if windows are open, they should not be used at the same time as an air conditioner. But they are useful even if you do have an air conditioner. They provide a less expensive alternative early and late in the cooling season, or at night, if it’s cool enough. The air conditioner can be used if the fan is not running.
Before arranging to have a whole-house fan installed, check with your local building department to see whether a permit is needed. Also, check the type of wiring that’s required.
Safe Use of Whole-House Fans
When operating a whole-house fan, be sure to open a sufficient number of windows. If you don’t, you may have a problem known as back-drafting — a situation in which outside air is drawn into your home through vent pipes such as the water heater flue. This introduces polluted air into your home. Check with the installer for recommendations on the safe operation of your system.
Remember, too, that for a whole-house fan to work, your attic must be adequately vented. It must provide a sufficient amount of roof venting to allow air to escape as quickly as it is being blown into the attic. Consult the manufacturer for recommendations. A general rule is to make sure your attic has the same amount of venting as the size of the hole you’ve created in the ceiling to mount the fan.
Buying a Whole-House Fan
When shopping for a whole-house fan, pay close attention to airflow ratings of different models. Airflow is rated in cubic feet per minute (cfm). The larger the home, the greater the airflow needed to cool it. The minimum airflow required to cool an entire home is equal to three times the square footage. For a 1,200-square-foot home, you’ll need a whole-house fan that moves 3,600 cfm.
Another feature to consider is variable speed — high for quick cooling and low (quieter) for less forceful air circulation. Different types of controls are also available, such as wall switches, pull cords, and timers. Louvers (or dampers) should open and close automatically when the fan is turned on and off. You can also choose between a direct-drive fan and a belt-driven fan. The direct-drive models are noisier, but the belt-drive fans require more maintenance.
To learn more about cooling your home with fans, see Simple Ways to Cool Your Home and Save Big,
This article is excerpted from Green Home Improvement by Dan Chiras. Dan teaches workshops on renewable energy and green building through the Evergreen Institute.