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Operating and Pressure-Test Air Changes Calculator

Calculate ACH from documented flow and volume while keeping operating outdoor or supply airflow separate from a stated pressure-test result.

Use this result well

Inputs that matter
Measured operating airflow (CFM), Served volume (ft³), Airflow basis, Sources and assumptions, and 3 more
Output to expect
Operating airflow and air changes, Pressure-test air changes
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Operating airflow and air changes

Convert a measured airflow and the volume it serves to air changes per hour. Identify whether the airflow is outdoor ventilation or total supply, which may contain recirculated air. This rate alone does not establish ventilation compliance or infection protection.

ACH = measured CFM × 60 ÷ served volume in cubic feet.

Pressure-test air changes

Normalize a documented building air-leakage test by enclosed volume. Keep its test pressure and configuration with the result. ACH at an imposed test pressure is not the natural air-change rate or operating ventilation.

Test ACH = measured test CFM × 60 ÷ tested volume; retain the actual test pressure.

Updated: September 2026

Example Scenarios

The built-in example is an arithmetic illustration. Replace it with your own verified measurements or planning assumptions.

→ 1.25 ACH

The built-in example is an arithmetic illustration. Replace it with your own verified measurements or planning assumptions.

→ 3 ACH at 50 Pa

FAQ

No. A flow measured under a test pressure is not natural infiltration or an operating ventilation rate. Save the pressure and basis, and use actual operating airflow for a separate calculation.

Use the actual source documents, units and operating conditions shown in the selected mode. Replace illustrative examples with your records, enter explicit zeros only where valid and retain unresolved assumptions.

Choose Save planning case for local history. Copy MD retains current inputs, notes and interpretation; Download CSV exports the result breakdown. Export a separate copy before changing devices or clearing browser storage.

About Operating and Pressure-Test Air Changes Calculator

Convert a measured airflow and the volume it serves to air changes per hour. Identify whether the airflow is outdoor ventilation or total supply, which may contain recirculated air. This rate alone does not establish ventilation compliance or infection protection. Normalize a documented building air-leakage test by enclosed volume. Keep its test pressure and configuration with the result. ACH at an imposed test pressure is not the natural air-change rate or operating ventilation.