Choosing Installing Bathroom Exhaust Fan

Choosing Installing Bathroom Exhaust Fan

Choosing And Installing A Bathroom Exhaust Fan

By Jim Sulski

Summary: Bathroom exhaust fans are a must. They decrease odors, mildew and save your paint and wallpaper. It can be difficult to install a bathroom fan in for the most experienced do-it-yourselfer. Jim explains how to select and install a bathroom exhaust fan.

For anyone who has been in a hot steamy bathroom, the benefits of an exhaust fan are fairly obvious.

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By pushing air out of a bathroom, exhaust fans alleviate foggy mirrors, dripping windows and bathroom odors.

They have a few long-term benefits as well. Exhaust fans remove excessive moisture, which can over time cause paint and wallpaper to peel, mildew to thrive, and even advanced problems such as rotting drywall and window frames.

The latest generation of bathroom fans is efficient and fairly quiet, and can be combined with lights and/or heaters. And they’re fairly affordable, ranging in price from about $40 to $100.

About the only disadvantage of exhaust fans is their installation — especially in older homes. The installation process will vary from house to house and takes some planning.


Before purchasing a fan, the first step is to take inventory of what your bathroom now has. If you already have a fan installed, the work to install a new unit may be minimal.

If you only have an overhead light fixture, be prepared to cut a hole through the ceiling to install a new fan.

And if you don’t have an existing light fixture in the bathroom, you’ll need to run an electrical line to ceiling to power the fan. That type of work will probably require the services of an electrician.

The next step of the installation process is choosing the correct fan capacity. A simple formula to determine fan capacity is to multiply the square footage of the room by 1.07. That number will give you the minimum amount of CFM — cubic feet per minute — needed to exhaust moisture and odor.

For example, a 10-foot-by-six-foot bathroom of 60 square feet multiplied by 1.07 would require a minimum CFM of about 65.


The best way to mount an exhaust fan is to install a wall unit on an outside wall. Ideally, such a unit is placed closed to the shower but far from the bathroom door. The ductwork out of the building is usually minimal.

Start the actual installation by shutting off the power to the existing light fixture or fan at the circuit breaker or fuse box. Remove the light fixture.

Remove the electrical box (it may be held on via a nut up on the inside top of the box, or screwed into a ceiling joist through the side). Next, try to determine where the ceiling joist is. You can use a nail or punch to help locate the joists through the ceiling or location them from the attic.

Exhaust fans are anchored to a ceiling by attaching them to a joist or joists. Depending on the fan, you may have to install support blocks on the inner side of joists to mount the fan housing.

The housing of some fans are mounted directly to one joist through openings on the side of the housing, or through mounting tabs on the exterior of the housing. Other housings use adjustable hanger bars to install the fan housing between two joists.

After locating the joists, next position the fan housing around the light fixture opening and trace the outline of the housing on the ceiling. Using a small handsaw, cut out the opening. Drywall ceilings will be much easier to cut that plaster ceilings, which require cutting through both plaster and lathe. Cut carefully, as plaster ceilings may crumble around the edges.

Next, place the housing in the opening and use a piece of folded cardboard or a wood shim to keep it place. The housing should be secured so that the collar or lip of the unit is flush with the ceiling.

Next, figure out the best way to run the ductwork coming out of the exhaust fan. In most cases, manufacturers recommend using ductwork to run the exhaust out of the attic and through a wall or the roof.

Some manufacturers recommend using flexible dryer hose — three-inch round ductwork — from the discharge on the fan to an opening that is cut in the wall or roof. A roof or wall cap is then installed from the exterior of the building to the end of the ductwork.

Finally, follow the manufacturer’s instruction to make the electrical connections. The connection of the pipe containing the existing wiring into the fan housing may require a few electrical adaptors available at most home improvement stores.

If you are installing an exhaust fan and light fixture; or a fan, light and heat lamp fixture, you’ll need to run additional wiring through the existing conduit if you wish to operate the various appliances separately.

by Jim Sulski. All rights reserved. February 9, 2005.

NOTE: This column is distributed by Real Estate Matters Syndicate, PO Box 366, Glencoe, Illinois, 60022. This column may not be resold, reprinted, resyndicated or redistributed without written permission from the publisher.

© 2005 by Ilyce R. Glink. Distributed by Real Estate Matters Syndicate.

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