How to Select a Bathroom Exhaust Fan

The air flow volume that a bathroom exhaust fan can move is rated in Cubic Feet per Minute or CFMs. Different sized bathrooms have different exhaust fan CFM requirements. To determine which CFM rating you’ll need, the square footage of your bathroom must be calculated and the number of toilets, showers, tubs, and whirlpool tubs must be taken into account.

The following information will show you how to calculate a proper CFM rating for your bathroom.

Bathrooms with 100 square feet or less

Powder rooms, for example, typically are smaller than 100 square feet. These bathrooms need 1 CFM per square foot, with 50 CFM being the minimum for any bathroom under 100 square feet.

Square footage is calculated by multiplying the length of a room by the width. Therefore, a 4ʹ x 6ʹ bathroom would have 24 square feet. Because the minimum rating for small rooms is 50 CFM, you would choose a fan with a rating of 50 CFM or higher. In another example, a 7ʹ x 9ʹ room has 63 square feet and would require a fan with a 63 CFM rating or higher.

Bathrooms with more than 100 square feet

To determine what ventilation is needed when bathrooms have more than 100 square feet, the number of fixtures—excluding sinks—must be accounted for.

Bathtubs, showers, and toilets each require 50 CFM; whirlpool or jetted tubs require 100 CFM.

A 10ʹ x 12ʹ’ bathroom has 120 square feet. Since the room is larger than 100 square feet, you would need to add up the CFM rating for each fixture, excluding sinks. Let’s say this 120 square foot bathroom contains 1 toilet, 1 shower, and 1 tub.

The toilet = 50 CFM, shower = 50 CFM, and the tub = 50 CFM. So altogether 150 CFMs are required for this bathroom.

Whether you are doing your first bathroom remodel or simply needed a refresher on exhaust fan requirements, you can use these guidelines—which have been established by the Home Ventilating Institute (HVI)— to figure out which type of exhaust fan is needed for your bathroom.

These 50 CFM fans have the minimum amount of ventilation for small bathrooms

A 150 CFM exhaust fan is perfect for 3 bathroom fixtures at 50 CFMs each

When installing the right exhaust fan, you may also need flexible ducts to reduce the number of joints or eliminate the need for elbows.

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