For moderate climates, a whole-house fan can reduce your need for air conditioning except for the hottest days. To keep your house cool, a whole-house the fan uses powerful suction to pull air from all parts of your home, creating cooling circulation and replacing hot, inside air with cooler outside air.
Maximum cooling from your whole-house fan
Whenever the outside temperature drops below inside temps, open some screened windows and flip on the fan to pull cool, dry air through the house and exhaust hot air through your roof vents.
For a morning “pre-cool,” run your whole-house fan just before sunrise, then close the windows to seal in the cool air as the day warms up. In the evening when outside temps dip, turn on your fan to cool off the house, which takes about 20 minutes for a 2,500 sq. ft. house.
In general, whole-house fans are more effective in multi-story homes than single-level. Also, certain regions of the country have better potential for whole-house fan cooling than others.
Design options for whole-house fans
Ceiling-mounted whole-house fans are the most popular. Installed in the attic between the ceiling and living space, they move large amounts of air.
Ducted whole-house fans are quieter because they are mounted in the attic, away from living space. Flexible ductwork runs from low-key room grilles to the fan. The air can be vented directly out of the house, rather than through attic vents.
Variable speeds let you flush air quickly through the house at high speed or create a continuous, gentle air flow at low speed.
Programmable thermostats and temperature controls add convenience, but make sure your house is prepared:
- Heating and cooling are turned off.
- No fire in the fireplace (so flames don’t get sucked out into the house).
- Windows are open (without enough ventilation from open windows, the powerful suction can create a dangerous backdraft from gas appliances).
Some models come with insulated doors that create an air seal. If you don’t have insulated doors, cover the fan in winter, or else it will be like leaving a window open. Just remember to take off the cover before firing up the fan come the first warm days of spring—and to open at least one window.
Sizing up your whole-house fan
The Home Ventilating Institute (which calls whole-house fans “whole-house comfort ventilators”) recommends a whole-house fan make a complete air exchange in 2 or 3 minutes—enough to create a perceptible “breeze” throughout the house.
The recommended flow rate is roughly calculated by multiplying the gross square footage of the entire house (including unoccupied areas like closets) by 2. For example, a 2,000-square-foot living space would need a whole-house fan with about 4,000 CFM (cubic feet per minute) of capacity.
Nevertheless, your house must also have an adequate amount of roof ventilation to exhaust the air flow. For this reason, consult a ventilation (HVAC) professional to determine the correct size unit and required exhaust area.
Costs and benefits of whole-house fans
Whole-house fans cost between $150 and $550, plus installation, which could cost about $1,000. You might also need additional roof vents put in.
Some municipalities and utility companies offer energy rebates for whole-house fans. According to the Sacramento Municipal Utility District, whole-house fans use about 10% of the energy an air conditioner uses and can pay for themselves in just a few seasons.