What are the pros and cons of attic ventilation fans?
Short answer. Powered attic fans can move a lot of air and lower attic temperatures on hot afternoons, but they use electricity, wear out, and can pull cooled air out of your house through ceiling gaps if the attic lacks enough intake. In most Georgia homes, balanced passive ventilation with soffit intake and a ridge vent does the job with fewer downsides.
Pros
- High airflow on hot, still days when passive vents move less air.
- Useful on roofs where passive exhaust is hard to install, such as some hip roofs.
- Thermostat and humidistat controls run them only when needed.
- Solar models avoid wiring and operating cost.
Cons
- Depressurization. A fan that moves more air than the soffits can supply pulls the difference from the house, through light fixtures, top plates, and the attic hatch. That can raise cooling costs instead of lowering them.
- Combustion safety. In homes with gas water heaters or furnaces in or near the attic, negative pressure can interfere with venting of combustion gases.
- Short circuiting. Paired with a ridge or gable vent, the fan often pulls air in through those openings, and can even pull rain in through a ridge vent.
- Maintenance. Motors, bearings, and thermostats fail, and dead fans often go unnoticed for years.
- Roof penetration. A large hole with flashing that can leak or be cracked by hail.
Bottom line
Building scientists widely recommend air sealing the ceiling and getting passive intake and exhaust right before considering a powered fan. If you already have one, make sure intake is generous and remove competing exhaust. Compare approaches in ridge vent vs box vents and roof ventilation basics.