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Calcimator

Air Change Rate Calculator

Calculate air changes per hour (ACH) from airflow rate and room volume with recommendations by room type.

Inputs

Results

Air Changes / Hour

8

Full Exchange Time (min)7.5
Recommended Min ACH4
Recommended Max ACH6
Meets Minimum (1=Yes, 0=No)1
How to Use This Calculator
  1. Enter Airflow Rate (CFM), Room Volume (ft³), and Room Type.
  2. Review the Air Changes / Hour result.
  3. Use Full Exchange Time (min) and Recommended Min ACH to inform your decision.

How the result changes with Room Volume (ft³)

Room Volume (ft³)Air Changes / Hour
100,0010.12
350,0010.03
650,0000.02
900,0000.01

What each input means

Airflow Rate (CFM)
Supply or exhaust airflow in cubic feet per minute.
Room Volume (ft³)
Total room volume: length × width × ceiling height in feet.
Room Type
1 = Residential, 2 = Office, 3 = Classroom, 4 = Hospital OR, 5 = Lab, 6 = Clean room.

What each result means

Air Changes / Hour
Number of times the entire room air volume is replaced per hour.
Full Exchange Time (min)
Minutes required for one complete air exchange.
Recommended Min ACH
Minimum recommended ACH for the selected room type.
Recommended Max ACH
Maximum recommended ACH for the selected room type.
Meets Minimum (1=Yes, 0=No)
Whether the calculated ACH meets the minimum recommendation.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    Airflow Rate (CFM) = 200, Room Volume (ft³) = 1500, Room Type = 1 = 3 input(s) provided
  2. Calculate Air Changes / Hour
    Air Changes / Hour = (airflowCfm * 60) / roomVolume
    8 = 8
  3. Calculate Full Exchange Time
    7.5 = 7.5
  4. Calculate Recommended Min ACH
    4 = 4

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