VENTILATION CFM
VENTILATION CFM
CFM = 0.03 × ft² + 7.5 × (Nbr + 1)
ft²
RESULT
—
FILL IN ABOVE
ASHRAE 62.2-2019. Tight homes (<3 ACH50) require mechanical ventilation. Estimate only — verify installed flow at the grille with a flow hood and confirm with a licensed HVAC contractor.
About this calculator
This ventilation CFM calculator gives the required mechanical ventilation rate for a residence per ASHRAE 62.2 (and the IECC residential ventilation standard that references it). The whole-house base rate is 0.03 CFM per ft² of conditioned floor area + 7.5 CFM per occupant, with occupancy assumed at bedrooms + 1. The calculator also lists the local exhaust CFM required for kitchens (intermittent vs continuous), bathrooms, and laundry per the same standard. ESTIMATE ONLY — actual installed flow must be measured at the grille with a flow hood and verified by a licensed HVAC contractor.
Common questions
Does an old leaky house need mechanical ventilation?
Per ASHRAE 62.2-2019, no — homes that test below 5 ACH50 on a blower-door test are required to have mechanical ventilation, but anything above can rely on infiltration. Practically: most pre-2000 homes are leaky enough to skip mechanical ventilation. Anything built or retrofitted to current code (3 ACH50 or tighter) needs it.
What is the best mechanical-ventilation strategy?
Three options. (1) Exhaust-only — just run a bath fan continuously at the calculated CFM. Cheap, depressurizes the house slightly. (2) Supply-only — duct outdoor air to the return side of the air handler. Pressurizes slightly, which keeps moisture out of walls in cold climates. (3) Balanced (HRV/ERV) — best, recovers 60-90% of heat or moisture from the exhaust stream.
How is bath exhaust counted toward whole-house?
A bath fan can pull double duty: provide the local 50 CFM exhaust during shower use, AND run continuously on a low setting to provide whole-house ventilation. Panasonic WhisperGreen and similar fans have dual-speed controls specifically for this. Cheaper and simpler than a separate whole-house exhaust fan.