A power attic vent, sometimes called an attic fan, is a mechanical, electrically powered fan mounted on the roof or gable that actively pulls hot air out of the attic rather than relying on passive airflow. It typically runs on a thermostat, switching on once the attic reaches a set temperature. A power vent can move more air than passive ventilation alone, but without enough matched intake, it can pull conditioned air up from the living space instead of fresh air from outside.
Most attic ventilation works passively, using the simple physics of hot air rising to draw air in low and push it out high with no moving parts and no electricity. A power attic vent changes that equation by adding a motorized fan, mounted through the roof deck or a gable wall, that actively exhausts attic air rather than waiting for natural convection to do the work.
Most power vents are controlled by a built-in thermostat, switching on automatically once the attic reaches a preset temperature and shutting off again once it cools, so the fan runs on demand during the hottest stretches of the day rather than continuously.
On paper, a power vent can move considerably more air than a passive system of the same size, which sounds like a straightforward upgrade. The catch is that a fan pulling air out of the attic has to pull that replacement air in from somewhere, and it will draw from the path of least resistance.
If the attic's intake vents, typically at the soffit, are not sized and sealed to supply enough air on their own, the fan can end up pulling conditioned air up out of the living space through ceiling gaps, recessed lights, and attic hatches instead of drawing fresh air in from outside, which actually increases cooling costs rather than reducing them.
A power vent is only as good as the intake behind it, which is why a proper installation sizes the soffit intake specifically to match the fan's exhaust capacity rather than adding a fan to whatever passive intake already exists.
For an attic that is already well vented passively, a power vent is not automatically an upgrade. It is worth having someone confirm the intake side can actually keep up before adding the mechanical exhaust.
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