Air Changes Per Hour (ACH) indicates how many times the air inside a room is replaced with fresh air within one hour. It is a critical parameter for ventilation design.
Room Volume = Area × Ceiling Height
ACH = (CFM × 60) ÷ Room Volume
Room Area = 500 sq.ft
Ceiling Height = 10 ft
Airflow = 800 CFM
ACH ≈ 9.6 Air Changes Per Hour
This calculation is widely used for hospitals, clean rooms, laboratories and commercial HVAC systems.
ACH (Air Changes Per Hour) indicates how many times the air inside a space is replaced in one hour.
Typical office spaces require around 4–6 ACH for adequate ventilation.
Hospital operating rooms often require 15–20 ACH for proper air quality.
Proper ACH ensures fresh air supply, removes contaminants and improves indoor air quality.