For moderate climates, a whole house fan can reduce your need for air conditioning except on the hottest most humid days.
Maximum cooling with a whole house fan
Whenever the outside temperature drops about 10 degrees below the inside temps, open the windows and turn on the fan to pull cool, fresh air inside the home and exhaust the hot stale air out through your attic 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 drops again, turn on your fan to cool off the house.
Whole house fans are very effective in multi-story homes where the heat rises making the upstairs much hotter than down stairs. Also, certain areas 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 most common. They are typically installed in the attic between the ceiling and living space.
Ducted whole-house fans are quieter than traditional whole house fans because they are mounted in the attic, away from living space.
A two-speed control allows you to quickly flush the hot air out of the house on high speed or create a continuous, gentle breeze on low speed.
Do’s and Don’ts
Make sure your heating and cooling system is turned off.
Windows must be open (without enough ventilation from open windows, the powerful suction can create a dangerous backdraft from gas appliances).
Make sure your whole house fan comes with a damper door to help create an airtight seal. If you don’t have a damper, it will be like leaving a window open.
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.