Ventilation requirements

Air changes per hour

An HVAC system is usually dimensioned based on the heat load of the space that requires cooling. But the required ventilation needs, depending on both application and occupation, are often overlooked. A simple air change calculation may assist in finding the right amount of fresh air ventilation.

Simple calculation

  • Use the table below to find the required amount of air changes per hour (ACH).
  • Calculate the volume of the space to be conditioned in either m3 (for SI units) or in ft3 (for I-P units).
  • Calculate the required airflow:
    • Airflow [m3/h] = Volume [m3] x ACH [h-1]
    • Airflow [CFM] = Volume [ft3] x ACH [h-1] / 60 [min/h]

Air changes table

The table below shows the required air change rate for a selection of common applications. Please consult the pdf document for an extended description and overview.

ApplicationAir changes per hour
All spaces in general≥ 4
Assembly halls4–6
Bakeries20–30
Banks4–10
Bars/nightclubs20–30
Churches8–15
Cinemas6–10
Classrooms6–20
Factory, ordinary4
Factory, fumes/moisture10–15
Fire stations4–10
Galvanizing plants20–30
Garages, repair20–30
Garages, storage6–10
Hospital rooms 6–8
Kitchens15–60
Laundries10–15
Libraries4
Machine shops6–12
Malls6–10
Medical centers/clinics/offices8–12
Museums12–15
Offices4–6
Police stations4–10
Post offices4–10
Poultry houses6–10
Precision manufacturing10–50
Residences4
Restaurants10–15
Supermarkets8–10
Swimming pools20–30
Theaters8–15
Warehouses6–30