Does your house seem to "lose its cool" in summer? Does excessive humidity in winter cause mold in the attic? An attic fan may be just what you need.
In summer, heat builds up in an unventilated or poorly ventilated attic where temperatures can easily exceed 150 degrees F. This attic heat finds its way into the interior spaces by either inadequate insulation or physical air leaks around pipes, cables, ducts and gaps in the structure. This creates an undue burden on the air-conditioning system.
In winter, heated moisture-laden air from everyday activities (cooking, showering) finds its way into the attic where it condenses on the cold underside of the roof structure. In some cases, heat trapped in the attic may melt snow on the roof, and cause ice dams at the cold eaves.
An attic fan augments the passive air circulation in the attic provided there are sufficient openings for air to enter the attic. With proper placement, an attic fan enhances the air circulation and brings the attic temperature to within 10 degrees of the outside temperature. There are three important steps to ensure the effectiveness of attic fans:
The ideal way to control the operation of an attic fan is with a thermostat and a humidistat. In summer, the thermostat operates the fan when the attic temperature reaches a preset level (usually 90 to 95 degrees F). In winter, the humidistat operates the attic fan when the relative humidity exceeds a preset level (usually 40 to 50%). This reduces attic moisture. Eliminating mold and mildew on the roof structure is the ultimate goal.