What this tool answers
You need a first-pass bathroom exhaust fan class for a US home bath. The calculator scales floor area by moisture load, then names the smallest class on this ladder (80, 110, or 130 CFM) — or returns NO_MATCH.
Why moisture load matters
Frequent showers and laundry rooms add moisture that a bare area rule understates. Factors 1.0 / 1.25 / 1.5 are transparent screens — not a psychrometric model of every bath.
Ducts and makeup air
Long or restrictive ducts reduce delivered airflow. Plan makeup air so the fan can move the named CFM. Confirm local code before buying.
When the answer is NO_MATCH
If CFM demand exceeds 130 on this ladder, the site returns NO_MATCH. Split zones, shorten ducts, or use a higher-CFM commercial fan — do not force a 130 CFM consumer class.
Sources
HVI-style ≈1 CFM per bathroom sq ft rule as the non-commercial primary. VEVOR US exhaust fan pages for 80 / 110 / 130 CFM (HTTP 200, 2026-09-10).