Cooling Your Dwelling With a Photo voltaic Attic Fan

A roof fan reduces heat build-up in attics by venting warm air through openings (roof vents) that are usually located on the gable ends or on the roof of the house. The air vented from the attic is replaced by cooler outside air, which is drawn in through reveal openings (openings on the underside of the eaves). By reducing the air temperature in the attic, the heat gain from the ceiling below is reduced – at least that’s the theory. The effectiveness of roof fans (including solar roof fans) in reducing air conditioning costs is somewhat controversial. Some experts say that blowing air out of the attic can actually draw cool air out of the living area through cracks in the attic. If you are installing a roof fan, make sure that any air leaks into the space under the attic are sealed.

If you are a skilled handyman with electrical and carpentry skills (such as laying wire and cutting and flashing holes in the walls or roof of your house), you can do this job yourself.

Shopping for attic fans

Before buying a solar roof fan, carefully measure your attic and check against the manufacturer’s specifications to see if the fan you are considering is sufficient. Homes with large attics may need at least two attic fans.

Installation of the solar roof fan

Solar roof fans are much easier to install than traditional electric roof fans because there is no need to run electrical cables. These are usually mounted in the roof and fed by a built-in 10 to 20 watt solar module (panel). The module generates direct current to run the fan.

To install a solar roof fan, cut an opening in your roof from the outside according to the fan manufacturer’s instructions and mount the fan flashing to prevent leaks. Working on a roof, especially on a steep roof, can be dangerous. Correct installation of turn signals is critical to avoid roof leaks.

Remember, attic fans need vents to draw outside air into the attic to replace the hot air they purge. Vents are usually located under the eaves (overhangs). An opening at the end of the gable may also suffice. When in doubt, contact a professional contractor and check the manufacturer’s requirements.

To work effectively, the solar electric module should be located in a sunny location so that it is either not shaded at all or only for a short time during the day.

Do not cut off any structural frame members when installing a solar roof fan. Measure two or three times to make sure you cut the right spot. Be careful when climbing ladders and also working on roofs.

While most solar roof fans are integrated units, at least one manufacturer, Solatube, makes a model that, like a traditional roof fan, can be mounted in a louvred gable-end opening. The solar-electric module is not part of the fan, as is the case with the roof-mounted solar roof fan. It is mounted separately in a sunny place on the roof. Cables from the solar module are connected to the fan in the attic.

When working in an attic, make sure you stand on ceiling joists so you don’t step through the drywall ceiling below. You may want to put a piece of plywood over the joists to serve as a work platform.

For more information on how to cool your home with fans, see Easy Ways To Cool Your Home And Save It.

This article is an excerpt from Green Home Improvement by Dan Chiras. Dan teaches workshops on renewable energy and green building at the Evergreen Institute.

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