How do I determine what size exhaust fan I need?

Although there are many factors that will determine what size exhaust fan you need, as a general rule, take the length times the width of your bathroom to come up with the square footage. Assuming the ceiling height is 8 feet, take the square footage and multiply it by 110% (or 1.1). This will give you the amount of ventilation needed for your bathroom. For instance a 10 foot by 10 foot bathroom with 8 foot ceilings would have a square footage of 100 sq. ft., take 100 times 110% to get 110. You would need an exhaust fan with 110 CFM to properly ventilate the bathroom. Heigher ceiling heights will require additional CFM.

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