Heating, Cooling & Ventilation calculator
Air Changes Per Hour Calculator
Calculate air changes per hour from room volume and measured or specified delivered airflow.
Calculate air changes per hour from room volume and measured or specified delivered airflow. Start with measurements from the actual job and use manufacturer or supplier figures wherever the form asks for coverage, yield, density, spacing or pack size. Watch actual airflow and room volume in particular. To calculate ACH, airflow must be converted to volume per hour and divided by room volume. Required ACH itself depends on the space and use.
What you need to enter
The Air Changes Per Hour Calculator uses the following project information to calculate the result.
- Room volume
- Airflow
Calculator result
Air changes per hour (ACH)
How the Air Changes Per Hour Calculator works
This page is built around ACH = airflow expressed as volume/hour ÷ room volume. Applied to air changes per hour from room volume and measured or specified airflow, the engine first converts compatible measurements to a common basis and then calculates air changes per hour (ach). Verify actual airflow and room volume before treating the output as a buying, sizing or set-out figure.
Air Changes Per Hour Calculator worked example
Air Changes Per Hour Calculator example: If a 60 m³ room receives 360 m³/h of measured airflow, ACH = 360 ÷ 60 = 6 air changes per hour. Use actual delivered airflow rather than only the fan's free-air rating when checking an installed system. This example shows the arithmetic only; on a live job, review actual airflow and room volume before turning the result into an order or final size.
Important calculation assumptions
For air changes per hour from room volume and measured or specified airflow, to calculate ACH, airflow must be converted to volume per hour and divided by room volume. Required ACH itself depends on the space and use.
Frequently asked questions
What should I check on site before using the Air Changes Per Hour Calculator?
Use room volume and actual delivered airflow. Convert airflow to volume per hour before comparing it with the room volume. On this page, the measurements are used specifically for air changes per hour from room volume and measured or specified airflow.
Which details about actual airflow and room volume should I verify for the Air Changes Per Hour Calculator?
To calculate ACH, airflow must be converted to volume per hour and divided by room volume. Required ACH itself depends on the space and use. For the Air Changes Per Hour Calculator, that is the main reason to verify actual airflow and room volume.
What should I verify after using the Air Changes Per Hour Calculator?
For the Air Changes Per Hour Calculator, use ACH to describe the delivered ventilation rate, not as proof that ventilation is adequate. Required air changes depend on occupancy, contaminants and room use. Use that check before committing to an order, layout or equipment choice.