Why Install an Attic Fan?
Is installing an attic fan worthwhile? Why should I install an attic fan? These are common questions because before you have one, it is hard to believe they can make much difference. But they make a big difference.
Your roof absorbs energy from the sun all day long and that heat transfers into your attic. You may be thinking "my attic is insulated, a fan isn't necessary". Many attics have insulation over the ceiling, but not between the attic space and the roof. In that case the attic still heats up. If you have insulation between the rafters, that will cut down on the heat somewhat, but it still gets plenty hot. Your attic may get up to 150° (F) during the day. All that hot air heats the ceiling, even with insulation. Plus, hot air expands and some of the air may be pushed into your home. The movement of air inside your home may also have the affect of drawing air from the attic into the living area.
Bottom line, the hot air in attic heats up your home, almost like a hot water bottle. By moving that trapped air out of the attic you can reduce your attic temperature dramatically.
"If I have air conditioning, why would I need an attic fan too?" An attic fan is cheap to operate and it reduces how much cooling is required from the A/C. You will reduce your A/C energy consumption by running an attic fan. Your home will cool down faster and you will save money.
How Does An Attic Fan Work?
An attic fan can be mounted behind a gable vent or through the roof. The fan is connected to a thermostat and turns on automatically when it reaches the set point (usually around 90°-100° F). The fan draws air through the attic and out through the vent.
An attic fan requires adequate make-up air. If the fan is blowing out 5 cubic feet of air per minute, there must be other openings in the attic to allow at least this much air in. The openings can be any combination of gable vents, ridge vents, eave vents, and roof vents. Ideally those openings are at the other end of the attic, to allow cross flow throughout the entire attic. The hot air is blown out and replaced with cooler air.