How to Size a Bathroom Vent Fan
Ask Danny, Kitchens and Baths, Repairs and Installation by Danny Lipford
What size exhaust fan should we use in our small (5’ x 7’) bathroom? –Tam
Hi Tam,
If your bathroom has an 8’ ceiling, the cubic feet per minute (CFM) rating for your fan should be as least as high as the number of square feet (5’ x 7’ = 35 sq. ft.) in the room. So in your case, a 50 CFM fan should work. A bathroom with a higher ceiling would require a larger fan.
To remove more of the moisture from the air when showering, use a bit larger fan (80-110 CFM). Also, be sure there is at least a 1” gap under the bathroom door to allow fresh air to enter the room when the door is closed.
You can find out more about bathroom fans, and how to calculate their size, at Not Your Old Bath Fan.
Good luck with your project,
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