How to Install a Bath Fan

Keep your bathroom comfortable and avoid foggy mirrors with a bath ventilation system


Bath fans are essential for removing moisture, heat and odors from the bathroom.

The video above will walk you step-by-step through a basic bathroom fan installation process, and the steps below detail a more thorough approach.


Cut the hole
Cut the hole - Install Bath Fan

Safety: Never vent to an attic or subfloor as moist air creates an environment for mold and mildew growth.

• Locate where you want to place the fan. We recommend placing it over a toilet - do not mount it above a tub or shower. Mark the location by inserting a 16d nail into the drywall at each corner so the nails will protrude into the attic.
• From the attic, locate the nails and mark the location of the fan with a pencil.
• Cut out the drywall or plaster with a drywall saw or reciprocating saw. Start your cut by drilling a hole in the drywall large enough to accept the saw blade.
• If there is no attic or if the roof is inaccessible, use a stud sensor to locate a joist from the bathroom. Cut the opening from below. Use the fan enclosure as a template.

Attach fan and block off insulation
Attach fan block off insulation - Install Bath Fan

• Attach the fan enclosure to the joist with screws.
• Cut or push back the insulation, leaving a 6-inch gap between the unit and insulation.
• Cut pieces of a 2 x 4 to fit between the joists, blocking off the fan from the insulation, and attach lumber with screws.

Cut hole in the roof
Cut hole in the roof - Install Bath Fan

Note: If you are installing a side vent, you can skip to Step 6.

• Trace a circle on the underside of the roof just large enough for the roof vent and tailpipe.
• Drill a hole large enough for the saw blade, then cut out the circle with a reciprocating saw, saber saw or keyhole saw.

Cut away shingles
Cut away shingles - Install Bath Fan

Remove the shingles from around the cutoff without damaging the underlying roof paper.

Install the roof vent
Install the roof vent - Install Bath Fan

• Install the roof vent by sliding the top flange under the shingles above it and resting the bottom flange on the shingles below.
• Apply roofing cement on the underside of the flanges to seal.
• Secure the vent flanges with roofing nails before installing the shingles.
• Install the shingles on the sides of the roof vent and apply roofing cement to seal the joint with the shingles. Start at the bottom and work your way up to the top of the vent.
• Slip the last shingle under the existing singles above the vent.

Connect the ductwork
Connect the ductwork - Install Bath Fan

• Slide clamps over the flexible duct at both the roof cap and the fan, then slip the clamps over the tailpieces of the roof vent and fan and tighten the clamps.
• Wrap the joints with duct tape.

Wire the fan
Wire the fan - Install Bath Fan

• Run cable to the fan and to the switch if no wiring is present. If you are installing a fan with a light, you’ll need to run three-wire cable from the switch to the fan.
• Connect wiring according to the manufacturer’s instructions.
• Plug the fan motor into the built-in receptacle.

Wire the switch
Wire the switch - Install Bath Fan

• For a fan and light switch with existing wiring, splice the white wires and connect the grounds securely with wire connectors. 
• Connect power to both switches through two pigtails spliced to the feed wire.
• Connect the red wire to one switch terminal and the black wire to the other terminal.