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How To Install A Bathroom Exhaust Fan

A properly functioning bathroom exhaust fan that is the proper size for the square footage of your bathroom is the most important fixture in your room. With out this simple fan, you can be causing unneeded damage to your home from the buildup of excess moisture during bathing and showering.

I have renovated many bathrooms during my career and replaced or added fans in every case, but If you own a home that has an air exchanger and it is vented to your bathroom, you should not need an extra bathroom fan. You could expect this job for a first timer to take about 4-5 hours to complete.

Difficulty Level: 6/12

Tools Required

Materials Required

Installing A Bathroom Fan

The first thing you should do is measure the size of your bathroom (square footage) and take that with you while shopping for your fan. The boxes will tell you what size room that fan is rated to exhaust. Once you are ready to start at home first decide where to place your new fan in the ceiling. Things to consider are trying to stay close to shower or tub (but not directly in those areas unless the fan is rated for “wet areas”).

Access to area above fan in attic is important as well because you will be hooking up exhaust venting so it must be accessible, try to position your fan where one side will be up against a ceiling joist so you can firmly mount it. Finally you need to watch for other obstacles in the ceiling like wood blocking or electrical wiring.

Now that you have a location chosen, remove the fan from the box and find the ceiling cut out template supplied by the manufacturer and trace it out on the ceiling. Take your drywall saw and cut out this area you have marked. If there was no ceiling joist in that location, install some wood blocking and secure the fan to it using the supplied directions from the fan manufacturer.

Cut ceiling drywall
Cutting the ceiling drywall. Note the ceiling joist on the right.

Next you will have to go into the attic space and cut a hole through your roof to mount the roof exhaust vent through. Cut this opening just large enough for the round end of the housing to fit through and no more than 8′ from the new bath fan if possible. Now take the vent up onto the roof and mount it to your roof by placing a bead of roofing tar around the hole you cut and lowering the round end of the vent into the hole.

Bathroom exhaust fan ducting
Here the homeowner is attaching the air ducting to the outlet from the fan box.

TIP: Place the upper row of shingles you cut through so that it overlaps the upper half of the vent base

Nail the vent down and run another bead of tar around the perimeter of the vent base that is exposed. Now you can go back into the attic and cut your insulated flex duct to length and attach it to the fan exhaust port and roof vent ends with the silver duct tape. You are now ready to have a certified electrician come and finish the electrical hook up to the fan and switch. By hooking the new fan into the existing light switch this will ensure that the fan is always on when anyone is showering or bathing. People sometimes forget to turn it on when it is on a separate switch by itself.

bathroom fan box
The installation is almost complete.