Isolation Room Air Changes Calculator
ACH, exhaust and purge time for isolation rooms.
Enter your values
Enter the room area in sq ft.
Enter the ceiling height in ft.
Enter the air changes in ACH.
Enter the removal efficiency in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
At a glance
| What it does | ACH, exhaust and purge time for isolation rooms. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Room area, Ceiling height, Air changes, Removal efficiency |
| Main output | Exhaust airflow |
| Formula | purge time = 60 x ln(1/(1-removal)) / ACH |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Room area(sq ft)
- Enter the room area in sq ft.
- Ceiling height(ft)
- Enter the ceiling height in ft.
- Air changes(ACH)
- Enter the air changes in ACH.
- Removal efficiency(%)
- Enter the removal efficiency in %.
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.
What do I need to enter into the Isolation Room Air Changes Calculator?
Just 4 values: room area, ceiling height, air changes, removal efficiency. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Isolation Room Air Changes Calculator work out the answer?
Airborne infection isolation rooms need at least 12 air changes per hour and negative pressure to the corridor. It applies the formula purge time = 60 x ln(1/(1-removal)) / ACH and shows the working so you can check each step by hand.
Is the Isolation Room Air Changes Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.