As summer progresses, there is an increasing accumulation of heat in the roof, beams, attic, walls and furnishings of the home. While it is true that some lowering of temperature of the home occurs during the night, summer nights are too short to allow for anything like an equalization of temperature.
Attics can reach temperatures of 150 to 160 degrees Fahrenheit during a summer day, although outside air temperatures are only 95 to 97 degrees Fahrenheit. The cooling load for a home air conditioner depends on the difference in temperature between the inside and outside air, and reduction of attic temperatures from 155 degrees to 105 degrees Fahrenheit will result in a significant reduction in cooling load. In a home with poor ceiling insulation, heat movement through ceilings may account for 30 percent or more of the total cooling cost. With a well-insulated ceiling, this source of heat may account for only 12 to 15 percent of the total cooling cost. Thus, high attic ventilation rates are most important for poorly insulated ceilings.
Therefore, an attic fan can not only dispel this heat, it can draw gentle breezes throughout the house whenever and wherever the home owner wants them. By the simple touch of a button, cooling breezes are wafted in through the soffit vents, sweeping the heat and stagnant air up through the attic fan and out of the house.