Most turn on and off automatically with a thermostat, so that it only runs when the attic needs to be vented. Even though they come in different sizes, bigger is not always necessary. Smaller fans use less power and still cover up to 2000 square feet of attic floor. Optional humidistat keeps attics dry during the winter months. Attic ventilation is required year round.
Most people associate attic vents with heat, but they are wrong.
There are two major forces working in the attic and heat is the second of them. Moisture is the most destructive. The winter air is drier, making your attic more susceptible to excessive moisture. Absorbing moisture from the home and its inhabitants. Producing mildew, or rotting conditions, damaging rafters, sheathing and destroying shingles.