A fan, which costs two to five cents per hour to operate, will make a room feel 4 to 6 degrees cooler. Also, a fan works well in tandem with an air conditioner because the dehumidifying action of the air conditioner provides drier air that the fan can then move around.
In frequently used rooms, install a ceiling fan (set it to spin counterclockwise in summer). You'll save the most money by running the fan only when you're in the room. A motion-detector switch (around $20), which turns the fan on when you enter a room and off when the room is empty, is a good addition. However, if you have pets that move in and out of the room, make sure the switch can be turned off manually. Otherwise, your pets can cause the fan to run while you're away.
If nighttime temperatures drop into the 70s where you live, you might want to purchase a whole-house fan, which runs $300 to $600 installed. This type of unit goes in an upstairs ceiling, ideally in a central hall. When run at night with the windows open, the fan will pull cool air into the house as it vents hot air out through the attic. Most models are designed to slip in between joists for easy installation. Whole-house fans, which draw only as much power as a couple of lightbulbs, are usually outfitted with a variable-speed switch and/or timer. If you install one, be sure to get an insulated box to cover the portal in winter.
Cost: Ceiling fans range from $40 to $300 or more. Floor fans cost around $20, and whole-house fans run from $300 to $600.
Benefit: Ceiling fans can decrease your cooling bill by up to 15 percent, while a whole-house fan can slash it by 50 percent.