When you know how air moves naturally through your home, you can then optimize your mechanical ventilation.

In warmer climates, natural ventilation can’t circulate enough air through a home to provide sufficient cooling at night to remove the day’s heat. Mechanical ventilation can provide continuously moving air that will keep your home cooler, day and night, with circulating fans, whole-house fans, and/or evaporative coolers.

The quality and energy efficiency of these devices varies widely. Shop carefully—it might be best to buy from a dealer who specializes in fans rather than from a department store.

Circulating Fans

Circulating fans include ceiling fans, table fans, floor fans, window fans, and fans mounted to poles or walls. These fans create a wind chill effect that will make you 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 set- ting about 4˚F with no reduction in com- fort. 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. 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. A36- 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 over- powering 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.