Required CFM from Air Changes per Hour

The inverse of the ACH formula.

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Formula

CFM = ACH × volume ÷ 60

Example calculation

4 ACH in 2,000 ft³ → 133 CFM.

Practical HVAC use

Size exhaust or ventilation fans.

Common mistakes

Ignoring code minimums, which may be per person or per area.

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Educational tool. Results are estimates from the stated formulas; always confirm with manufacturer data and the code adopted in your jurisdiction. All calculators