Isolation Room Air Changes Calculator
ACH, exhaust and purge time for isolation rooms.
Enter your values
ⓘ Live results
Results
- Exhaust airflow
- 324 CFM
- Supply airflow
- 249 CFM (75 CFM offset)
- Purge time
- 34.5 minutes
- Room volume
- 1,620 cu ft
- Pressure target
- -2.5 Pa (-0.01 in wc) minimum
Quick answer
Airborne infection isolation rooms need at least 12 air changes per hour and negative pressure to the corridor.
purge time = 60 x ln(1/(1-removal)) / ACH
How to use the Isolation Room Air Changes Calculator
- 1Enter room dimensions and the required air changes — 12 ACH for new AII rooms.
- 2Set exhaust above supply by at least 50-75 CFM to hold negative pressure.
- 3Wait the purge time before the room is re-entered without protection.
Worked example
Using the values the calculator loads with:
Inputs
- Room area180 sq ft
- Ceiling height9 ft
- Air changes12 ACH
- Removal efficiency99.9 %
Results
- Exhaust airflow324 CFM
- Supply airflow249 CFM (75 CFM offset)
- Purge time34.5 minutes
- Room volume1,620 cu ft
- Pressure target-2.5 Pa (-0.01 in wc) minimum
Frequently asked questions
Why 99.9% removal?
It is the standard benchmark for clearing airborne contaminants between patients.
Protective environment rooms?
Those are positive pressure with HEPA supply — the opposite of an isolation room.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.