Ventilation (Air Changes) Calculator
Calculate required ventilation airflow from room dimensions and air changes per hour.
Estimates for planning purposes only. Verify against local ventilation codes and consult a qualified HVAC professional before installation.
How it works
- 1Enter the room’s length, width, and height in metres or feet.
- 2Select the room type to apply its recommended air changes per hour (ACH).
- 3The calculator multiplies volume × ACH ÷ 3600 to give airflow in m³/s, m³/h, L/s, and CFM.
Use cases
- Sizing an extract fan or MVHR unit for a bathroom or kitchen.
- Verifying an office meets minimum fresh-air ventilation requirements.
- Estimating duct and fan capacity for a whole-house strategy.
Frequently asked questions
What does air changes per hour (ACH) mean?
ACH is how many times the room’s air volume is replaced per hour. A 40 m³ bedroom at 5 ACH needs 200 m³/h (≈ 118 CFM).
How is required airflow calculated?
Q (m³/s) = volume × ACH ÷ 3600. A 54 m³ kitchen at 10 ACH needs 0.15 m³/s = 540 m³/h ≈ 318 CFM.
Which standard defines ACH values?
ASHRAE 62.1 (commercial) and 62.2 (residential) are widely used. Local codes may set higher minimums — check the authority having jurisdiction.
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