How often should an attic fan run?
Short answer. A powered attic fan should run only when the attic is hot, which in Georgia usually means summer afternoons and early evenings, switched on and off by a thermostat often set somewhere around 100 to 110 degrees. It should not run around the clock or through the winter; constant running points to a low setting, a failed control or an attic starved of intake.
A normal pattern
- Summer: the fan kicks on late morning or midday, runs through the hot part of the afternoon, and shuts off in the evening as the attic cools.
- Spring and fall: it runs on warm afternoons only, some days not at all.
- Winter: it should rarely run. If a humidistat runs it in winter, it may be pulling heated air from the house.
Signs it runs too much
- It runs all night in summer.
- It runs in cool weather.
- It never seems to shut off even when you turn the dial up.
Possible causes: a thermostat set too low, a stuck relay or control, or not enough intake, so the fan never cools the attic enough to shut off.
Signs it does not run enough
On a hot afternoon, if the fan is silent, turn the thermostat down. If it starts, the setting was too high. If it does not, check the breaker, the control and the motor.
Attic fan or whole house fan?
A whole house fan is a different machine with a different schedule: you run it on mild evenings and mornings with windows open, when the outdoor air is cooler and drier than the indoor air. In Georgia's muggy summers that window is short, so whole house fans see most use in spring and fall.
If the fan runs constantly, consider whether the attic needs it at all. See roof ventilation basics and attic heat and shingles.