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Air Changes per Hour Calculator

Nominal air changes for a well-mixed room; actual removal effectiveness is separate.

Nominal air changes for a well-mixed room; actual removal effectiveness is separate.

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Result

Enter your values and run the tool to see your result.

What this tool does

Divides airflow by room volume to give air changes per hour. Both figures must use matching unit bases.

How to use it

  1. Enter the ventilation airflow.
  2. Enter the room volume on the same unit basis.
  3. Run it for air changes per hour.

Worked example

Flow 500 and volume 100 give 5 changes per hour. Using m³/h for flow and m³ for volume keeps the units consistent.

Calculation method

Air changes per hourflow/volume

Frequently asked questions

My fan is rated in CFM.
Multiply CFM (ft³/min) by 60 for ft³/h, and enter the volume in ft³. Mixing unit systems throws the result off badly.
What rate is appropriate?
It varies by use — homes, offices, kitchens, and labs all differ. Consult your ventilation standard or local code; this tool does not recommend a target.

What this tool does not cover

A nominal rate assuming perfectly mixed air. Short-circuiting, dead zones, filter efficiency, and actual contaminant removal are not reflected.

References