Convert a stated air-change rate into an airflow quantity

Air changes per hour describe airflow relative to a room's volume. The calculation is useful when a required rate has already been specified. It does not determine which rate is appropriate for a room or activity.

Calculate the enclosed volume

An illustrative room 5 m long, 4 m wide and 2.7 m high has a volume of 54 m³. At a hypothetical specified rate of four air changes per hour, the nominal airflow is 54 × 4 = 216 m³/h. Dividing by 3.6 converts that to 60 L/s.

Check what air is being counted

Fresh outdoor air, extracted air and recirculated air are different streams. A recirculating fan's rated airflow does not automatically provide the same amount of outdoor air. Record which stream the requirement describes.

Treat rated performance carefully

Actual airflow depends on the installed system, including resistance and operating conditions. A catalogue fan rating alone may not establish delivered airflow in the room. Where performance matters, use an appropriate system design and measurement process.

Keep the calculation bounded

The example rate is not a recommendation or a compliance requirement. Room use, occupancy, contaminants and other factors may govern the actual ventilation design. The calculator converts a supplied rate and volume into a nominal airflow; it does not verify indoor air quality or select a ventilation system.

Found a measurement or calculation issue? Send the example and your correction.