For example, a 100-square-foot bath would require a 110 CFM-rated fan. To determine which size fan to buy for your bath, multiply the room's square footage by 1.1. The bathroom here is below an accessible attic, so Tom ran the exhaust duct across the attic and out a gable end.īathroom vent fans are rated by how many cubic feet of air they can move in one minute, known as the CFM rating. That's why we asked This Old House general contractor Tom Silva to show us how. One reason many households still don't have bath fans is that they can be intimidating to install. Step 1: Bath Vent Overview Photo by Keller & Keller PhotographyĪ bathroom without a ventilation fan is like a fireplace without a chimney: If you fail to pull the moisture generated in the bathroom out of there, it will migrate into the walls and grow mold and mildew, or blister paint and peel wallpaper. Also, the installation of the bathroom exhaust fan will go much quicker if you ask a spouse or friend to help be in the attic while you work from below, or to hand you tools while you're on the ladder. Note that the bathroom vent fan must always exhaust to the outdoors never allow the duct to simply blow into an attic, crawlspace or other enclosed area. Other venting options includes running the duct up through the roof or down through the soffit. In this particular installation, Tom ran the exhaust duct into the attic and through a sidewall to the outdoors.

Here, This Old House general contractor Tom Silva shows the proper way to install a bath vent fan.

But more importantly, it will help prevent moisture-related problems, such as the growth of mold and mildew. Installing a ventilating fan in your bath will help eliminate fogged-up windows, steamy mirrors and stale odors.

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