Solar Attic Fan

A solar attic fan is powered by solar photovoltaic (PV) panels, which means that it cools the attic with little or no grid electricity.
Photo credit: John S. Quarterman

Attic fans are used to cool hot attics by pushing out warm indoor air and pulling in cooler outdoor air. Attic fans reduce heat and moisture buildup, which decreases both cooling costs and damaging condensation. This prevents mold, fungal decay and ice damming as well.

A solar attic fan is powered by solar photovoltaic (PV) panels, which means that it cools the attic with little or no grid electricity. They may be operated by a switch, or automatically adjusted by a thermostat.

Downsides of Attic Fans

While attic fans certainly have benefits, there has been some debate about the possible downsides of attic fans (solar and conventional power).

In the 1990s, a Advanced Energy Corpstudy showed that in houses with poorly sealed and insulated attic floors, attic fans caused excessive moisture, depressurization, and could cause danger because of combustion. Also, it pointed out that using fans to ventilate the home used more energy.

Also in the 1990s, another study by the Florida Solar Energy Center found that solar attic fans lowered annual energy use by 460 kWh per year, which is a relatively low ROI.

However, these studies had small sample sizes and were limited to small geographic areas. Therefore, we recommend solar attic fans as a good investment, because they should reduce energy consumption by lowering the temperature in your attic. Just make sure that your attic floors are sealed and insulated to prevent the aforementioned issues.

Free LEED Exam PreperationInstalling an Attic Fan

We recommend that you find a vendor that can include a battery with the fan, because without one, the fan stops working every time the sun goes behind a cloud. In addition, we recommend installing a thermostat so the fan only works when you want it to work. This will increase the life of the fan.

When purchasing an attic fan, make sure that it is the right size in cubic feet per minute (CFM). To determine the ideal size, consider the volume of the attic. Typically, attics need 10 air changes per hour. The volume of your attic (L*W*H) in cubic feet multiplied by the number of air changes per hour (10) divided by 60 equals the number of CFM required.

For a simpler method, try this calculation from the Home Ventilating Institute (HVI): to find the desired CFM, multiply the square footage of your attic by 0.7. Then add 15% if you have a steep or dark roof, or 30% if your roof is both. So, for example, if you have a 500 square foot attic, you would need a fan with a CFM of 350.

HVI also recommends dividing the amount of CFM required by 300 to determine the soffit intake vent area.

It is best to purchase a fan that comes with a battery and a thermostat. The battery will prevent the fan from stopping every time the sun isn’t out, and the thermostat will allow you to control when the fan is on or off (which will extend the life of the fan).

Also, proper installation of the attic fan is important, because without proper air sealing and insulation, the fan could pull air conditioned air out of the house, which will make the air conditioner work harder and use extra energy. For an effective attic fan, make sure that the attic is well ventilated with natural air flow.

Whether this is something you can do yourself all depends on your home repair skill level. If you've never done any type of roofing, leave it to the pros. If you're pretty handy and have done some roof repair before, you may be able to do it yourself.

Solar Attic Fans and LEED

Because they do not operate on grid electricity and reduce energy costs, they may contribute to buildings that are looking to become certified under the LEED green building rating system.

According to LEED for New Construction 2009, the a solar attic fan could contribute to the following credits:

• Energy and Atmosphere (EA) Prerequisite 2: Minimum Energy Performance (0 points)
This credit establishes a minimum level of energy efficiency for buildings, based on energy costs. Solar attic fans save energy and reduce cooling costs, potentially contributing to this credit.

• EA Credit 1: Optimize Energy Performance (1-19 points)
This credit rewards LEED projects for achieving energy efficiency beyond the minimum set forth in EA Prerequisite 2. Points are awarded based on the energy cost savings percentage - the higher the percentage, the greater the number of points awarded. Again, solar attic fans reduce cooling costs, it could help to earn this credit.

Examples of Solar Attic Fans

One example of a product that is currently available on the market is the Solatube Solar Attic Fan.

Solatube International, best known for its daylighting products, was founded by Steve Sutton, the inventor of the tubular skylight. Based in Vista, California, the company produces the “Solar Star” attic fan, which is powered by a 10 W or 22 W solar panel. It uses no grid electricity, so it has no operation cost, and is designed to withstand all types of weather conditions. Therefore, the fan provides ventilation, saves energy, extends the roof life, and reduces mold, so it pays for itself over time.

The Solar Star has a 5 year warranty on the solar panel and motor and a 10 year warranty on all other parts.

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