On hot summer days, the air in an uninsulated attic can heat up to 130 to 150 degrees Fahrenheit. Sure, you could just stay out of the attic on warm days, but the problem is the heat built up in the attic will seep down through gaps in the ceiling and make the rest of the house hotter as well.
Not only does the increased heat make your home stuffy and uncomfortable, it also makes your air conditioner work harder and raises your summer energy bills. An attic ventilating fan can significantly help to alleviate this problem.
A ventilating fan in the attic can lower the attic’s temperature as much as 20 to 30 percent, and in the rooms directly below by up to 10 to 15 %. The cooling is accomplished through replacement of heated interior air by cooler exterior air, rather than by air conditioning and dehumidification.
Attic fans will are controlled by a thermostat that is set to turn the fan on when the air in the attic heats to a certain temperature, and to shut off the fan when the temperature falls below a certain point.
Many attic fans also are equipped with a firestat, which shuts the fan off at extreme high temperatures so that the fan does not draw fire and/or smoke into the attic during a house fire.
Another control that is added in areas of high humidity is a humidistat, which will enable the fan to remove moisture from the attic during the winter. This helps prevent formation of ice dams on the roof. It can also prevent damage and rot in rafters and other roof framing members caused by ice buildup inside the attic.
Attic ventilation fans are either of the centrifugal or propeller type. They draw the cooler air from the exterior into the house’s lower stories and discharge it through windows or grilles in the attic.
Fans should be capable of at least 30 air changes per hour the size of the attic to be ventilated. Care should also be taken to select a fan that is quiet in operation. A low maintenance model is always preferable, so check the manufacturer’s recommended lubrication schedule. Fan motors with sealed bearings don’t need any lubrication, so look for that feature.
In the spring, prior to the onset of warmer weather, fan blades and housings need to be cleaned, for maximum efficiency, as do all window screens, vent screens and other vent openings such as soffits.