Installing a Bathroom Vent Fan
Putting in bathroom ventilation is one of the most requested retrofits, and it only requires a day's work.
Show us a bathroom with peeling paint, rotting window trim and a mold problem and we'll show you a bathroom without a vent fan. Bathrrom ventilation is the best way to prevent moisture-related problems, such as the growth of mold and mildew. Here, This Old House general contractor Tom Silva shows the proper way to install a fan, running the exhaust duct into the attic and through a sidewall to the outdoors.
Other venting options includes running the duct up through the roof or down through the soffit. Note that the fan must always exhaust to the outdoors; never allow the duct to simply blow into an attic, crawlspace or other enclosed area, or you're certain to fail inspection.
Bath Vent Overview
A 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. One reason many households still don't have bath fans is that they can be intimidating to install. That's why we asked This Old House general contractor Tom Silva to show us how. The bathroom here is below an accessible attic, so Tom ran the exhaust duct across the attic and out a gable end.
Bathroom vent fans are rated by how many cubic feet of air they can move in one minute, known as the CFM rating. To determine which size fan to buy for your bath, multiply the room's square footage by 1.1. For example, a 100-square-foot bath would require a 110 CFM-rated fan. Fans also have a sound rating, measured in sones. (A modern refrigerator operates at about one sone.) Vent fans range from as low as 0.5 sone up to about 6.0 sones. You'll find both the CFM and sone ratings printed on the vent fan's box.