Mechanical

Air Changes Calculator

Calculate air changes per hour from airflow and room volume, or calculate required airflow from target ACH.

Use this calculator for quick ventilation checks where room dimensions and either airflow or target air changes are known. It can be used either to calculate ACH from a known supply or extract airflow, or to determine the airflow required to achieve a target ACH.

Inputs

Calculation Mode

Room volume is calculated from length × width × height. Airflow results are shown in both L/s and m³/h for convenience.

Result

Air Changes
-
Enter values and click calculate.

Method

Room volume is calculated from the room dimensions:

V = L × W × H

Where airflow is known, air changes per hour are calculated from:

ACH = Q ÷ V

using airflow in m³/h.

Where target ACH is known, the required airflow is:

Q = ACH × V
  • V = room volume (m³)
  • L = room length (m)
  • W = room width (m)
  • H = room height (m)
  • Q = airflow rate (m³/h)
  • ACH = air changes per hour
  • Calculated result = -

Reference

  • This calculator provides a simple air change relationship between room volume and airflow rate.
  • ACH can be useful for preliminary ventilation checks, especially where a room-volume based design approach is being considered.
  • Final ventilation design should still be checked against the relevant occupancy, pollutant load, building use and project-specific compliance route.
  • Where applicable, final design should align with Approved Document F, BB 101, project specifications and manufacturer requirements.
Design note: This calculator is an indicative estimating tool only. Final ventilation requirements may depend on occupancy, internal gains, contaminant sources, supply and extract strategy, ventilation effectiveness and project-specific design criteria.

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