Ceiling fans are considered the most effective of these types of fans, because they effectively circulate the air in a room to create a draft throughout the room. If you use air conditioning, a ceiling fan will allow you to raise the thermostat setting about 4°F 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. Install a fan in each room that needs to be cooled during hot weather. Turn off ceiling fans when you leave a room; fans cool people, not rooms, by creating a 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 to 9 feet above the floor and 10 to 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 the walls.
Larger ceiling fans can move more air than smaller fans. A 36- or 44-inch diameter fan will cool rooms up to 225 square feet, while fans that are 52 inches or more should be used in larger rooms. Multiple fans work best in rooms longer than 18 feet. Small- and medium-sized fans will provide efficient cooling in a 4- to 6-foot diameter area, while larger fans are effective up to 10 feet.
A larger blade will also provide comparable cooling at a lower velocity than a smaller blade. This may be important in areas where loose papers or other objects will be disturbed by a strong breeze. The fan should also be fitted to the aesthetics of the room—a large fan may appear overpowering in a small room.
A more expensive fan that operates quietly and smoothly will probably offer more trouble-free service than cheaper units. Check the noise ratings, and, if possible, listen to your fan in operation before you buy it.
When buying ceiling fans, look for the ENERGY STAR® label. Fans that earn the label move air 20% more efficiently, on average, than standard models.
Window fans use little energy and can provide effective cooling in many climates. Window fans are best used in windows facing away from the prevailing wind and exhausting hot air from your home. To cool as much of your home as possible, tightly close windows near the fan and open windows in rooms far from the fan, preferably on the windward side of your home. Windows near cooler, shaded outdoor areas provide the best intake air.
In multi-level houses, the fan should be located on the upper level, if possible, and the open windows should be located on a lower level. If that's not practical, you may want to independently ventilate each level of your home with separate fans.
Depending on the layout of your home, you might want to use several window fans working together to pull the air through your home. For instance, fans in several upstairs bedrooms will assure that each bedroom is cooled, and will work together to pull air in through the rest of your home.