Fans can save you a bundle on air conditioning costs if you know how to use them. Scientists, studying human comfort in the 1950s, discovered that people felt about 4 degrees cooler in rapidly moving air than in still air because of the wind-chill effect. You can create a wind chill, using ceiling fans, table fans, floor fans, and other circulating fans in occupied rooms of your home. Circulating fans are people-coolers, so it does no good to leave them running in rooms with no people.
Another way to cut air conditioning costs is to circulate cool night air with or without fans. Your home is a solar collector that sucks up solar heat all day. During heat waves the house itself just gets hotter and hotter. If the outdoor temperature gets cool enough at night, you can use the night air to carry the heat out of your home by running fans all night.
Whole-house fans and window fans are used for flushing the home with cool night air. A whole house fan is a large specially designed fan, installed in the ceiling. The whole-house fan blows house air into the attic, where the air exits through oversized attic vents. Or instead, you can use one or several window fans. A window fan may be pointed to blow air into or out of the house. Push air in at some cool outdoor location facing the prevailing winds. Use another window fan to pull air out on the home’s leeward side (side of the home not facing the wind). Experiment with different configurations of fans to see which works best.
Passive ventilation works in mild summer weather: wait until evening, when the outdoor air is cooler than the indoor air, and open doors or windows in the parts of your home that are the hottest. Try to establish a cross-breeze by opening doors or windows at opposite ends of your home. Take advantage of any outdoor breeze by opening the doors or windows that will direct that moving air into your home, and remember that the outside air will be coolest on the shady side of your home or underneath trees or bushes.
Install screens on the doors or windows you find work best for ventilation to keeps bugs, leaves, and debris from getting into your home.You can also use fans to help move air through your home, following the same guidelines as passive cooling to decide when and where to ventilate. Try using a portable box fan fastened in a window, or a pedestal fan near an open door.
Night-flushing with fans works best in drier climates where the outdoor temperature dips into the low 70s or below at night. Don’t worry about over-cooling your home. Just wear a sweatshirt in the morning. And in the morning, close the windows and drapes before the outdoors heats up to preserve your cooled indoor environment – hopefully until the afternoon.