Pros and Cons Of Attic Fans
Mechanical ventilation is typically accomplished with a small fan located on a dormer vent. These fans are usually hardwired into a house’s electrical system and are controlled by a thermostat. They usually draw electricity in the range of 2 to 70 kWh per year, depending on local weather conditions and your attic temperatures. The cost of this energy of course depends on the local price of electricity.
Approximately one square foot of ventilation is recommended for every 150 square feet of floor area. You would have to check the specifications of the particular fan you are considering to determine the equivalence to regular vents.
One alternative to mechanical venting is a combination of ridge vents and eave or soffit vents (see diagram below). Ridge vents run along the ridge of your roof, and eave and soffit vents are located at the base of the roof. With this combination, the natural convection of the hot air in your attic powers the venting. In addition, because of the locations of the inlet and outlet vents, virtually the entire attic space is vented, reducing the likelihood of pockets of hot air.
Mechanical venting can provide adequate venting for your house, but is dependent on electricity. Other forms of venting, such as the ridge/soffit combination mentioned above, provide superior venting, but require modification of your roof to install. If you were already planning on installing a new roof, you should seriously think about a ridge/soffit combination.
Source:radiant-heat-floor-methods.com/