Hot Aisle Containment Calculator
Return airflow needed for a contained hot aisle.
Enter your values
Enter the total rack supply airflow in CFM.
Enter the aisle length in ft.
Enter the aisle width in ft.
Enter the containment height in ft.
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.
- Required return airflow
- 8,400 CFM
- Containment volume
- 768 cu ft
- Turnover rate
- 656.3 volumes/hr
- Recommended return grille area at 500 FPM
- 16.8 sq ft
Quick answer
Contained hot aisle return airflow should match total rack supply airflow, with volume sized to avoid excess dead space.
Return CFM = supply CFM x 1.0-1.1
At a glance
| What it does | Return airflow needed for a contained hot aisle. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Total rack supply airflow, Aisle length, Aisle width, Containment height |
| Main output | Required return airflow |
| Formula | Return CFM = supply CFM x 1.0-1.1 |
| Cost | Free — no sign-up, no download |
How to use the Hot Aisle Containment Calculator
- 1Sum the supply airflow of all racks feeding the hot aisle.
- 2Measure the containment aisle length, width and height.
- 3Size return grilles or ducted returns 5-10% above supply to keep the aisle slightly negative.
Inputs explained
- Total rack supply airflow(CFM)
- Enter the total rack supply airflow in CFM.
- Aisle length(ft)
- Enter the aisle length in ft.
- Aisle width(ft)
- Enter the aisle width in ft.
- Containment height(ft)
- Enter the containment height in ft.
Worked example
Using the values the calculator loads with:
Inputs
- Total rack supply airflow8000 CFM
- Aisle length24 ft
- Aisle width4 ft
- Containment height8 ft
Results
- Required return airflow8,400 CFM
- Containment volume768 cu ft
- Turnover rate656.3 volumes/hr
- Recommended return grille area at 500 FPM16.8 sq ft
Frequently asked questions
Why oversize return slightly?
It prevents hot air from leaking around end doors back into the cold aisle.
Cold aisle containment instead?
Use the same supply-matches-demand principle but seal the cold aisle instead.
What do I need to enter into the Hot Aisle Containment Calculator?
Just 4 values: total rack supply airflow, aisle length, aisle width, containment height. 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 Hot Aisle Containment Calculator work out the answer?
Contained hot aisle return airflow should match total rack supply airflow, with volume sized to avoid excess dead space. It applies the formula Return CFM = supply CFM x 1.0-1.1 and shows the working so you can check each step by hand.
Is the Hot Aisle Containment 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.