Guides / Renovation · Published 2026-11-01
Bath fan size: 1 CFM per sq ft, 50 CFM minimum, vented outside
50 CFM is the minimum, not your size.
Bathroom fans are the cheap line item that protects your expensive tile. For baths up to 100 sq ft, the common sizing rule is about 1 CFM per sq ft, with 50 CFM as the floor: an 8 × 10 ft bath wants about 80. Over 100 sq ft, add 50 CFM each for toilet, shower and tub, and 100 for a jetted tub. The duct matters as much as the fan: vent outdoors, never into the attic, and keep it short and straight. Choose 1 sone or less so people actually use it, and run it about 20 minutes after a shower.
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