A ceiling fan during hot, sticky days creates a wind chill effect that will make you feel more comfortable in your home, even if it's also cooled by natural ventilation or air conditioning. If you use air conditioning, a ceiling fan will allow you to raise the thermostat setting about 4 degrees with no reduction in comfort. In temperate climates, or during moderately hot weather, ceiling fans may allow you to avoid using your air conditioner altogether. A ceiling fan is recommended in each room that needs to be cooled during hot weather. Ceiling fans should be turned off when you leave a room; fans cool people, not rooms, through the wind chill effect.
Ceiling fans are only appropriate in rooms with ceilings at least eight feet high. Fans work best when the blades are 7-9 feet above the floor and 10-12 inches below the ceiling. Fans should be installed so their blades are no closer than 8 inches from the ceiling and 18 inches from walls.
In the winter months, ceiling fans will not reduce your heating costs, because the movement of air currents will cool our bodies slightly. This cooling effect may prompt residents to unnecessarily raise their thermostat and overheat their homes.
For more on the use of fans to cool one's home, visit the U.S. Department of Energy website.