Bathroom Fans by CFM

100 CFM or Less

101 to 200 CFM

201 to 400 CFM

Over 400 CFM

Sizing Guidelines

Bathroom exhaust fans are rated for their capacity to move air in cubic feet per minute (CFM). In simplest terms, the higher the CFM rating, the more powerful the fan. To quickly estimate the minimum amount of CFM needed, we recommend 1 CFM of air for every square foot of floor space. A 100 sq ft bathroom would therefore require a fan which can move at least 100 CFM. Other factors like high humidity and long lengths of ducting will require higher CFM fans.

But, if your bathroom is 100 sq. ft. or more in size (lucky you), the equation is different. Instead of depending on square footage, you’ll have to chime in with the different fixtures your bathroom holds to determine the fan’s proper CFM rating. HVI recommends the following CFM for different bathroom fixtures:

Shower - 50 CFM

Toilet - 50 CFM

Bathtub - 50 CFM

Whirlpool tub - 100 CFM

So, if your bathroom is more than 100 sq. ft. and has both a shower and a toilet, you will need an exhaust fan with at least a 100 CFM rating. Have a bathtub, as well? The CFM rating gets bumped to 150.

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