Which is better, a ridge vent or an attic fan?
Short answer. For most homes, a ridge vent paired with good soffit intake is the better choice: it runs all the time with no electricity, has no motor to fail, ventilates evenly, and cannot pull cooled air out of the house. A powered attic fan can make sense where a ridge vent will not fit, but the two should not be used together on the same attic.
Side by side
- Energy: ridge vents use none. Fans draw power, though solar fans run off their own panel.
- Maintenance: ridge vents have no moving parts. Fan motors and thermostats wear out, and a dead fan is just a hole in the roof.
- Coverage: a ridge vent draws evenly from every rafter bay. A fan pulls hardest from the area around it and can leave corners stagnant.
- Moisture: ridge vents work day and night, all year. Most fans run on temperature, so in winter they rarely run when moisture is the problem.
- House air: a fan with weak intake depressurizes the attic and pulls cooled air from the house through ceiling gaps, and can backdraft gas appliances located in the attic. A ridge vent cannot create that kind of suction.
When a fan can make sense
Hip roofs with very short ridges, complex roofs where a continuous ridge vent is not possible, and attics with plenty of intake that still overheat may benefit from a fan. Even then, intake has to be sized for the fan's airflow.
Why not both
A fan near a ridge vent pulls air in through the ridge a few feet away, sometimes along with rain, while the soffits do almost nothing. If you are adding a ridge vent, disconnect and remove the fan and deck over the hole. Leaving an old fan in place unplugged still leaves a penetration to maintain and a path for that same short circuit. See ridge vent vs box vents and attic heat and shingles.