Cooling Your Home With a Solar Attic Fan

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  The photovoltaic panel that powers a solar attic fan should be located where it will capture direct sunlight. The fan may be mounted to exhaust hot air through a roof vent or a gable-end vent.
  ILLUSTRATION: KEITH WARD
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  If outside temperatures are in the 90- to 110-degree range, the attic temperature can climb to 150 degrees. Even 105-degree outside air, when circulated through a 140-degree attic, will lower the temperature.
  ANIL RAO/RS MEANS

An attic fan reduces heat buildup in attics by removing warm air through openings (attic vents) typically located on the gable ends or on the roof of the house. The air that’s vented from the attic is replaced by cooler outside air drawn in through soffit vents (openings on the underside of the eaves). Reducing air temperature in the attic reduces heat gain through the ceiling below — that’s the theory, at least. The effectiveness of attic fans (including solar attic fans) in reducing air conditioning costs is somewhat controversial. Some experts say that blowing air out of the attic may actually draw cool air out of the living area through cracks in the attic floor. If you install an attic fan, be sure all air leaks to the space below the attic are sealed.

If you are an experienced do-it-yourselfer with electrical and carpentry skills (for example, running wire and cutting and flashing holes in the walls or roof of your home), you can tackle this job yourself.

Shopping for Attic Fans

Before you buy a solar attic fan, measure your attic carefully and check with the manufacturer’s specifications to be sure the fan you’re considering will be sufficient. Homes with large attics may need at least two attic fans.

Solar Attic Fan Installation

Solar attic fans are much easier to install than conventional electric attic fans because you don’t have to run electrical wires. These are typically mounted in the roof and powered by a built-in 10- to 20-watt solar-electric module (panel). The module generates direct current (DC) electricity to run the fan.

To install a solar attic fan, cut an opening in your roof from the outside, according to the fan manufacturer’s specifications, and mount the fan with flashing to prevent leakage. Working on a roof, especially a steeply pitched one, can be dangerous. And correct installation of flashing is crucial to prevent roof leaks.

Remember that attic fans require openings to draw outside air into the attic to replace the hot air they’re purging. Vents are usually located under the eaves (overhangs). A gable-end opening may also suffice. When in doubt, consult a professional contractor and check the manufacturer’s requirements.