Install a Bathroom Exhaust Fan

Bathroom exhaust fans are one of those installations that feel more complicated than they actually are. The real work isn't the fan itself—it's getting the ductwork to the outside without creating a moisture trap or a pathway for pests. A properly installed fan moves wet air out of your bathroom before it migrates into walls and attic framing, where it causes rot, mold, and structural damage that costs thousands to fix. Done well, it runs quietly, moves air reliably, and you never think about it again. Done poorly, you'll hear it struggling, or worse, you won't hear it working at all while water damage quietly accumulates behind your walls.

1. Map Your Route First. Kill the power to the bathroom at the breaker box. Decide whether you're venting through the roof, gable wall, or soffit—avoid the attic entirely. Measure the distance from the fan location to your exit point. If it's more than 25 feet, you'll lose efficiency; if you have more than four elbows in the run, you're fighting the fan. Mark your ceiling hole location in the center of the bathroom, away from joists if possible.
2. Cut with Precision. From above (in the attic), use your ceiling hole saw or template to drill a guide hole through the ceiling at your marked location. Go downstairs and cut out the hole using a drywall saw. Stay clear of electrical wires, plumbing, and framing. If you hit a joist, move your location 16 inches in either direction—you'll fit between studs on 16-inch centers.
3. Seal the Exit Point. Cut your exit hole through the roof, wall, or soffit using the proper hole saw for your duct diameter (usually 4 or 6 inches). From the outside, insert your vent cap or termination fitting, seal around it with roofing cement or exterior caulk, and secure according to the cap's instructions. If you're going through the roof, flash the opening properly or water will find its way in. For wall vents, ensure the cap is rated for your climate and has a damper.
4. Slope Toward Exit. Cut your flexible ductwork to length—route it as directly as possible toward your exit point. If you're in the attic, run it along the joists. Slope the ductwork slightly downward toward the exit so condensation drains out, not back into the fan. Secure it with duct clamps every 3 feet. Do not use zip ties or cheap clamps—use proper metal hose clamps that won't crush the duct. Connect the fan end to the ducting using a clamp or the ductwork connector on the fan housing.
5. Secure to Joists. Lower the fan housing through the ceiling opening. If it has mounting brackets, secure them to the ceiling joists using screws or bolts—the housing needs to be rock-solid, not resting on drywall. Attach the ductwork connection to the fan's outlet collar. Once mounted and ducted, you can secure the trim ring or mounting collar to the drywall with the fasteners provided.
6. Wire to Code. Run new electrical wire (12-2 or 14-2 NM cable, depending on your breaker size) from an available breaker in your panel to the fan location, or tap into existing bathroom wiring if a spare wire runs overhead. Bathroom exhaust fans should be on a 15- or 20-amp circuit dedicated to ventilation or shared only with the bathroom light. Strip 6 inches of sheathing from the cable, connect black to the fan's black wire (hot), white to white (neutral), and bare copper to the fan's ground lug. Secure the wire in place with clamps every 4.5 feet.
7. Install Control. Mount a single-pole wall switch or a humidity-sensing timer switch in a convenient location near the bathroom entrance or mirror. Wire it according to the switch manufacturer's instructions—usually black wire from the circuit breaker to the switch, then to the fan. Use a 15-amp switch rated for fan loads. If installing a timer, follow its specific wiring diagram. Test the switch before closing up any walls or ceilings.
8. Seal Every Gap. Once the fan is mounted and wired, seal any gaps between the fan housing and drywall with silicone caulk or non-expanding foam. Caulk around the trim ring to prevent air leakage. At the exit point (roof, wall, or soffit), apply exterior caulk or roofing cement to seal where the duct meets the vent cap. Seal any gaps around the ductwork inside the attic where it passes through the ceiling—this prevents unconditioned air from leaking into the bathroom.
9. Mount the Grille. From below, insert the trim ring through the ceiling hole and screw it to the fan housing. Slide the grille into the trim ring and secure it with the provided clips or springs. The grille should sit flush against the ceiling with no gaps. Make sure the damper (flapper) inside the grille moves freely.
10. Power Up and Verify. Go to the breaker box and flip the circuit breaker back on. Return to the bathroom and test the switch—the fan should run smoothly and quietly. You should feel air being pulled toward the grille, and condensation should not form on a bathroom mirror within 15–20 minutes of a hot shower. If the damper flapper sticks or the fan sounds strained, you likely have a ductwork blockage or excessive elbows in the run.