Calculate the minimum CFM rating you need for a bathroom exhaust fan based on room size and fixture count.
Bathroom Dimensions
HVI recommends 8 air changes per hour for bathrooms under 100 sq ft and 1 CFM per sq ft for larger bathrooms.
Fixtures
Add 50 CFM for each toilet and 50 CFM for each shower or tub in the space per HVI guidelines.
Usage and Duct Run
Heavy use means multiple people sharing the bathroom or frequent long showers.
Longer duct runs reduce effective CFM. Add 25% to your CFM requirement for every 25 ft of duct.