Bathroom Exhaust Fan Buying Guide

Sizing by CFM

• The Home Ventilating Institute suggests about 1 CFM per square foot for bathrooms up to 100 square feet (a 5×8 bath needs about 40 CFM; many choose 50 or more).
• For larger bathrooms, a common approach is about 50 CFM each for the toilet, shower and tub, and 100 CFM for a jetted tub.
• Long or twisting duct runs reduce airflow; choose a bit more capacity.

Noise

Fan noise is rated in sones. Around 1.0 sone or less is quiet; quiet fans get used, loud ones get switched off early.

Controls

• Timer switch: runs the fan for a set time after a shower.
• Humidity-sensing fan or switch: turns on automatically when humidity rises.
• Continuous low-speed ventilation: useful in tight, newer homes.

Installation details that matter

• The fan must vent outdoors through a roof or wall cap, never into the attic.
• Use the duct diameter the fan specifies, insulated in cold attics.
• A fan over a tub or shower must be listed for that location, and may need GFCI protection.
• Look for ENERGY STAR certification.

Professional exhaust fan installation averages about $400 (bathroom cost guide). Replacing a fan is a good add-on during any bathroom remodel.