Formula for Calculating Number of Air Changes in an Area (ACPH)

Number of air changes/hour in an area is

Total Room Airflow In CFM x 60
Total Volume of room in cubic feet

For calculating Total Room Airflow in CFM, first calculate air flow of individual filter. Formula is given below.


Air flow (in cfm) = Avg.air velocity in feet/Minute x Effective area of filter
Then find Total air flow. Formula is

Total Air flow = Sum of air flow of individual filter.


Air flow Velocity can be measured with the help of Anemometer.