How to Install an Attic Exhaust Fan for Better Air Conditioning Efficiency

Install an attic exhaust fan by cutting a roof or gable opening, mounting the fan unit, connecting power through your electrical panel, and sealing all penetrations to remove hot air and reduce cooling costs.

  1. Pick Your Fan Type First. Decide between a roof-mounted or gable-mounted fan based on your attic layout. Roof fans work best near the ridge line, while gable fans install in existing vents or new openings in the gable wall. Measure your attic square footage and buy a fan rated for 10-15 air changes per hour. A 1,200 square foot attic needs a fan moving 1,500-2,000 CFM.
  2. Plan Wiring Before Cutting. Shut off power at the main breaker. Plan your electrical route from the panel to the fan location. Most exhaust fans need dedicated 15-amp circuits. Run 14-2 Romex cable through the attic to your fan location, leaving 12 inches of extra wire. Install a wall switch near the attic entrance for manual control, or wire directly to the fan for thermostat operation.
  3. Cut Carefully Between Rafters. For roof installation, locate rafters and mark your opening between them. Use the fan housing template to trace the hole from inside the attic. Drill pilot holes at corners and cut with a reciprocating saw from the roof. For gable installation, remove existing vent louvers or cut a new opening using the manufacturer's template. Remove any insulation around the work area.
  4. Seal Housing Tight to Structure. Fit the fan housing into the opening from inside the attic. The housing flange should sit flat against the roof decking or gable wall. Secure with the provided screws every 6 inches around the perimeter. Apply roofing cement around roof installations and caulk gable installations to prevent air leaks.
  5. Weatherproof Every Penetration. Install the roof cap or gable louvers from outside, following the slope of your roof. Secure with appropriate screws and seal all penetrations with roofing cement or exterior caulk. The cap should sit flush and create a weatherproof seal. Check that the dampers move freely and close completely when the fan is off.
  6. Verify Airflow Direction Works. Wire the fan motor according to the manufacturer's diagram, typically connecting black to black, white to white, and green to the grounding screw. Install wire nuts and secure all connections in the junction box. Connect the thermostat if using automatic operation, setting it for 90-100 degrees. Restore power, test the fan operation, and verify proper airflow direction.
  7. Balance Intake and Exhaust. Install soffit vents or additional ridge vents to provide makeup air for the exhaust fan. You need 1 square foot of intake for every 300 CFM of exhaust capacity. Without proper intake, the fan will work harder and may pull conditioned air from your living space through ceiling penetrations.