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When to Run an Attic Fan

Keith Allen

The purpose of an attic fan is to remove heated air from the attic space. This serves several purposes, including improving the efficiency of the home and extending the life of shingles and roofing materials. Operating the attic fans on the proper schedule improves the efficiency of the ventilation system in providing a more comfortable and energy-efficient home.

Run the Fan all Day

Vents in attics help eliminate heat in the upper portion of the home.

Run the attic fan during the daylight hours during warm summer weather. Sunlight on a roof produces heat in the attic. Running the fan when the energy of the sunlight is striking the roof removes the heat that accumulates in the attic.

When It’s Hot

If the attic is warmer than the desired indoor temperature and warmer than the outside air, operating the attic fan makes the home more comfortable. Operating the attic vent fans beyond sunset may be necessary during hot weather. This can be a problem if the noise of the fan interferes with nighttime sleep.

Preventing Ice Damage

During the winter, a warm attic can cause ice dams. Warm air rising through the attic can melt snow on the roof. When this water runs down the roof, it freezes when it reaches the portion of the roof above the eaves of the home. This forms an ice dam that prevents future snowmelt from running off the roof. This water backs up and can get under shingles, causing leaks and damage.

Thermostatic Control

Thermostatically controlled fans require adjustment a couple of times per year. During the summer the fan should operate anytime the attic temperature is above the comfort level desired for the indoor living quarters. For example, if the air conditioning thermostat is set to 74 degrees, the attic fan might be set to 75 degrees. During the winter the attic fan thermostat should be set below the freezing point to prevent ice damming on the roof.