Adding a Bathroom Fan
A quiet fan, airtight ductwork, and a leak-free vent combine to clear moisture from the bathroom and the house.
Synopsis: A remodeling contractor offers a step-by-step guide to the installation of a bathroom fan, stressing the importance of preventing any moist air from leaking into the attic. A sidebar in the PDF below illustrates how to wire a high-tech switch that will keep the fan running for 20 minutes after you leave the room.
If you’re like me and enjoy a hot shower, the last thing you want in your bathroom is a fan that sounds like a helicopter. The reality is that hot showers create moisture that, left alone, will lead to mold and mildew problems. Lucky for us, the bathroom fan has come of age.
Today’s fans are quieter and move more air than yesterday’s models. Whether I’m building a new house or remodeling a bathroom, I install an ultra-quiet exhaust fan because a quiet fan is more likely to be used. And a properly installed fan clears excess moisture from the bathroom and the house to where it is unable to find a way back in. The fan should be near the shower, and the ductwork should be airtight and vented out the roof or a gable-end wall. Vapor exhausted through a soffit often will be drawn back into the attic through the soffit vents. The entire system must be airtight to keep moisture from leaking into the attic or wall and ceiling cavities.
Once installed, the fan must be used properly. As long as moisture is in the bathroom, the fan should continue to run. To eliminate the risk of it being left on for hours at a time, I install a delay-timer switch with the fan, which keeps it running for up to 60 minutes.
This may sound like a lot of work for a bathroom that has a window in it. But as a remodeler, I’ve seen the mold and mildew problems that moisture can cause. Opening a window is a good idea, but it isn’t reliable enough to eradicate moisture effectively.
Protect the bathroom and yourself
Cut the ceiling and keep clean with a plastic bag and a plastic suit.
Cheap and easy dust containment. A garbage bag taped to the bathroom ceiling catches dust while the ceiling is cut. A plastic suit (available at paint stores for less than $10) protects your skin from fiberglass insulation and dust in the attic.
Use a template and blocking for accuracy and convenience. A cardboard template cut from the fan’s box marks the cut in the attic. A piece of blocking screwed to the drywall extends beyond the cutline to catch the scrap when it is cut free. Leaving the screw loose allows you to twist the blocking out of the saw’s path.
Prevent air leakage in the attic
Sealant, blocking, and screws secure the fan.
Keeping moisture out of the attic is critical. The two key points are installing a leak-free duct and keeping air from the bathroom from leaking around the fan.
Sealant prevents moisture from leaking into the attic. A thick bead of sealant around the perimeter of the hole creates an airtight bond between the fan’s flange and the drywall. Place the fan in the hole carefully, and make sure it sits flat on the ceiling and sealant.
For more photos and details on installing a bathroom fan, click the View PDF button below.