Guide to Solar Attic Fans

Types of Solar Attic Fans

• Solar fans fall into two broad categories: solar roof fans and solar gable fans. The roof fan is installed on the roof so the solar panel has full sun exposure. A solar gable fan is installed on the gable of the house, and may be more suitable for homes with minimal exposure on the roof due to shade trees. The roof-mounted fan, however, is more effective.

How Solar Attic Fans Work

• Solar attic fans work on the same principle as electrically powered attic fans. The fans circulate the air while simultaneously pulling heated air out of the attic. The air exchange cools the attic space and so reduces the workload on your cooling system. The difference is that solar fans have a small solar panel on the exterior base. The interior attic fan is powered by the sun rather than electricity.

Solar Fan Sizes

• The size of your attic determines the volume of air within your attic. All the air needs to be circulated, with 10 exchanges of air per hour recommended for optimal efficiency. Solar fans are sized by how many cubic feet of air they move per minute, so a small solar attic fan may be sized at 800 cubic feet per minute, or 800 CFM.

  Find the volume of your attic space by multiplying the length by width by height. The result is the cubic foot volume of your attic. Multiply that by 10 and divide that result by 60 to determine the movement rate required to properly cool your attic. For example: Your attic measures 40 feet long by 20 feet wide by 6 feet high. The volume is 4,800 cubic feet. Multiply that by 10 (the desired rate of air exchange) for a result of 48,000. Divide that by 60 (hourly rate of exchange) for a result of 800. One small solar attic fan, sized 800 CFM may be sufficient to move the air in this smaller-sized attic. The larger your attic, the larger-sized fan and/or more fans needed to achieve the necessary exchange rate to cool the attic. Solar attic fan sizes range from 800 CFM to 1,550 CFM, though exact sizes vary by manufacturer.

Solar Fan Savings

• The initial cost of a solar fan ranges from $200 to $300 up to about $600, as of 2011. The initial cost, like many solar-powered technologies, is higher than that of an electrically powered attic fan. The average cost of running an electric attic fan is approximately $60 to $100 a year, dependent on local electrical costs and regional weather conditions. The cost of running a solar fan is zero. A savings in cooling costs may be realized within two years.