Air Changes per Hour Calculator
Calculate actual air changes per hour, target airflow, required fan quantity and operating energy for a rectangular room.
Default project preview
6.67 ACH
Room volume
2,700 ft³
Target airflow
270 CFM
Fans needed
1
Target difference
0.67 ACH
Calculator
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Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Imperial ACH = CFM × 60 ÷ room volume in ft³. Metric ACH = airflow in m³/h ÷ room volume in m³. Required fan count is rounded up.
FAQ
Air Changes per Hour Calculator questions
What does one ACH mean?+
One air change per hour means airflow equal to the room volume is supplied or removed each hour.
Does fan free-air rating equal installed airflow?+
Not always. Ducts, filters, grilles and pressure resistance can reduce actual airflow.
Can this determine a required ventilation rate?+
No. The target must come from the room use, occupancy, contaminant control and applicable standards.