Solar Powered Attic Exhaust Fans

There is a tremendous amount of anecdotal evidence supporting the use of attic exhaust fans. If installed correctly they will slow the increase and speed the decrease of summertime attic temperatures. Depending on the capacity the fan is capable of delivering, (this is dependent on both its size and a number of different installation variables,) a properly sized fan may also reduce the maximum temperature a residential attic is subjected to. Yes, they can lower the cooling load in a home, which may translate into greater comfort. Will they lower the cost of cooling your home? This is much more difficult to say. These fans do not use nearly as much power as an air conditioning compressor, but they do run a lot. It is difficult to find someone in residential efficiency who will not tell you that proper attic ventilation is important, but it is difficult to find anyone who will tell you that the energy benefit exceeds the energy needed to run them.

What if you didn’t need to worry about the power needed to run the fan? Solar powered attic exhausts are becoming popular home energy projects. This is actually a very good use of solar power. They are using the problem, (solar radiation,) to solve the problem. They also tend to have acceptable install cost as no new wiring needs to be run. And the fan itself is frequently housed outside the attic space making any inspection or repair possible without entering the attic. The one drawback to solar exhaust is that the attic could likely use additional ventilation when the fan stops at night. This may be an acceptable loss as the cooler nights in our area will typically lower attic temperatures to equal the outside air temperature by the start of the next day.

What you need to know regardless of the fan you choose:

Whether you choose a solar-powered or grid-tied exhaust fan— the correctness and quality of the install will likely have an enormous impact on the measure’s effectiveness. The installer should know something about attic ventilation and home construction. Many attics suffer from very inadequate relief to make up for the air being exhausted. This not only makes a hotter attic, but can create a negative pressure that will pull conditioned air out of the living space. Increasing the negative pressure without attic makeup air can make this problem worse. An attic exhaust installed in an attic with insufficient makeup air may even pull air in backward from the roof vents. The air just on top of the roof surface will be the only air in the area that is hotter than the attic. You don’t want to make your problem worse.

Make sure your installer is concerned with the available makeup air. They may want to add makeup ventilation to what is already available. Remember, a warmer attic in the winter is an energy benefit. You may want to only add ventilation for the summer that may be closed in the winter.

All attic exhaust fans are not equal. Check the claimed cfm exhausted for the unit.

As with all contracted work, it is a good idea to get more than one quote.

Lastly, INSULATION, INSULATION, INSULATION. Idaho Power has an incentive to help homeowners increase their level of attic insulation. An attic exhaust should not be pursued without adequate attic insulation. To learn more, visit www.idahopower.com/homeimprovement.