Can you have a ridge vent and an attic fan together, or should you choose one?
Short answer. You can physically have both, but you generally should not: a powered attic fan near a ridge vent tends to pull outside air in through the ridge vent instead of through the soffits, which short circuits the airflow and can even draw rain in. If you have to choose, a ridge vent with good soffit intake is usually the better system.
What happens when they share an attic
A fan creates suction. Air takes the easiest path to replace what the fan removes, and the closest large opening is often the ridge vent a few feet away, not the soffits at the far eaves. The result is a loop of air between the ridge and the fan while the lower attic stays hot and damp. During storms, that suction can pull wind driven rain through the ridge vent.
Ridge vent or attic fan: how to choose
- Choose the ridge vent if you have a gable roof with a reasonable ridge length and soffit intake. It is passive, silent, has no motor to fail, and works day and night.
- A fan may make sense on a hip roof with very little ridge where box vents cannot provide enough exhaust, and only with generous intake.
- A "ridge vent fan" is not really a combined product; powered fans are separate roof or gable units.
If you already have both
- Switch off the fan, or set its thermostat so it never runs, and watch attic temperatures and moisture through a season.
- If the ridge vent and soffits keep things dry, remove the fan at the next reroof and patch the opening with decking and shingles.
- If you decide to keep the fan instead, the usual advice is to close the ridge vent so the fan draws from the soffits, which means giving up the ridge vent.
Keep in mind that a switched off fan is still a large opening that acts like a passive vent and can still compete with the ridge vent. See ridge vent vs box vents and roof ventilation basics.