Air Changes per Hour (ACH) Calculator

Your details

Interior length of the room.
ft
Interior width of the room.
ft
Floor-to-ceiling height of the room.
ft
Airflow delivered by the HVAC unit, air purifier, or ventilation system. CFM = cubic feet per minute; CMH = cubic metres per hour.
CFM
Total number of air purifiers, fans, or HVAC outlets supplying air to this space.
Air Changes per HourAdequate ventilation
4.44ACH

Number of times the full room volume is exchanged each hour

Room volume2,700
Total airflow200
Time to remove 99% of contaminants62min
Time to remove 99.9% of contaminants93min
Airflow per sq ft / m20.67
4.44 ACH
Very low<2Low2-4Adequate4-6Good6-12High intensity12+

Your ventilation rate is 4.44 ACH.

  • Room volume is 2700 ft3. The full air volume is exchanged 4.44 times every hour.
  • At 4.44 ACH, it takes about 62 minutes to remove 99% of airborne contaminants (first-order decay model).
  • Removing 99.9% takes about 93 minutes. Doubling the ACH halves both removal times.
  • This is in the adequate range. The CDC recommends at least 5 ACH to help reduce airborne pathogen exposure in shared spaces.

Next stepTo increase ACH: add an air purifier (look for CADR rating), increase HVAC fan speed, or open windows to introduce fresh air. Use reverse mode to find the exact CFM target.

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