A whole-house fan will be effective even when the sun sets late in the evening. The fan will begin to cool the house once the outside air temperature drops below the interior temperature. A breeze feels cool on the skin, so even on warm evenings the fan will help simply by circulating air. Keep the fan going all night to cool off interior surfaces, and the house will feel cooler longer the next day. Turn it off early the next morning before the house begins to warm up. The fan should be located at the high point of the house to take advantage of the natural rise of warm air. Whole-house fans are typically installed in the attic, blowing air out the attic vents.
To maximize the cooling benefit from the fan and to keep your house cooler longer into the day, shade your south and west walls during the summer. Two good strategies are planting trees and installing exterior blinds over the windows during the summer (interior blinds will not help). In your climate, heating is a greater expense than cooling, so the trees should be deciduous. Once the leaves fall, you will benefit from the sun's passive heat.
A whole-house fan will contribute to heat loss in the winter, so you should install an insulated cover over the fan during the heating season. You may want to cover the attic vents as well.
Cooling your home with a whole-house fan uses roughly a tenth the energy it would take to air condition the same space. And whole-house fans don't cost a lot to install. Flex Your Power offers purchasing tips. For more information on sizing and installation, visit the Department of Energy website.
For more information:
This pdf fact sheet from the Department of Energy website offers detailed information about whole-house fans.
Learn more about how you can improve your home's energy efficiency with GreenHomeGuide?s Know How articles.