How can you tell if an attic fan is working?
Short answer. The quickest test is to turn the fan's thermostat down on a warm day: the fan should start within moments, run smoothly and quietly, and stop when you turn the dial back up. You can also look for the blade spinning through the dome from the ground, feel air moving toward the fan in the attic, and check the breaker or, for a solar fan, whether the panel is in sun.
Step by step
- Thermostat test: in the attic, find the control, note the setting and turn it all the way down. The fan should start.
- Listen: a steady hum is normal. Grinding, squealing or rattling points to bearings or a loose blade.
- Feel the airflow: near the eaves, you should sense air moving inward on a calm day.
- Turn it back up: the fan should stop. If it keeps running, the control may be stuck.
If it does not start
- Check the breaker and any switch near the fan.
- Try spinning the blade by hand with the power off. If it is stiff, the motor bearings may be seized.
- A hum without spinning often means a failed capacitor or motor.
- For solar fans, check that the panel is clean and in full sun, and the wiring connection is intact.
From outside
On a hot afternoon, look at the dome with binoculars. You may see the blade through the screen or feel warm air at the edges from a ladder. Look for cracks or dents in the dome, especially after hail.
Working is not the same as helping
A fan that runs fine can still pull air from the house if intake is short, or through a ridge vent if both are on the same attic. If the attic stays hot or upstairs rooms feel worse, check intake. See roof ventilation basics and ridge vent vs box vents.