Most attic fans rely on a thermostat to give the signal to turn on. The thermostat will work automatically, but you still need to set the temperature at which the fan should turn on. It is recommended to keep your attic fan temperature between 100 and 110 degrees Fahrenheit. This should work for an average attic fan user. If you live in a state that gets especially hot, hike the temperature higher to keep the fan running for longer.