Fume Hood Sash Airflow Calculator
Exhaust airflow for a lab fume hood by sash opening.
Enter your values
Enter the sash width in ft.
Enter the sash opening height in ft.
Enter the target face velocity in FPM.
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 exhaust airflow
- 600 CFM
- Sash open area
- 6 sq ft
- At full sash (say 2x height)
- 1,200 CFM
- VAV note
- Variable air volume hoods track this in real time as the sash moves
Quick answer
Laboratory fume hoods typically hold 80-120 FPM face velocity at the sash opening; airflow must rise as the sash is opened wider.
CFM = sash width x sash height x face velocity
At a glance
| What it does | Exhaust airflow for a lab fume hood by sash opening. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Sash width, Sash opening height, Target face velocity |
| Main output | Required exhaust airflow |
| Formula | CFM = sash width x sash height x face velocity |
| Cost | Free — no sign-up, no download |
How to use the Fume Hood Sash Airflow Calculator
- 1Enter the sash width and current opening height.
- 2Enter your lab's target face velocity, commonly 100 FPM.
- 3Use a VAV hood controller so airflow tracks sash position automatically for energy savings.
Inputs explained
- Sash width(ft)
- Enter the sash width in ft.
- Sash opening height(ft)
- Enter the sash opening height in ft.
- Target face velocity(FPM)
- Enter the target face velocity in FPM.
Worked example
Using the values the calculator loads with:
Inputs
- Sash width4 ft
- Sash opening height1.5 ft
- Target face velocity100 FPM
Results
- Required exhaust airflow600 CFM
- Sash open area6 sq ft
- At full sash (say 2x height)1,200 CFM
- VAV noteVariable air volume hoods track this in real time as the sash moves
Frequently asked questions
Constant air volume vs VAV?
CAV hoods hold airflow constant and face velocity varies with sash position; VAV hoods hold face velocity constant and vary airflow, saving energy.
What if velocity is too low?
Contaminants can escape into the room; check for obstructions, sash position and exhaust fan performance.
What do I need to enter into the Fume Hood Sash Airflow Calculator?
Just 3 values: sash width, sash opening height, target face velocity. 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 Fume Hood Sash Airflow Calculator work out the answer?
Laboratory fume hoods typically hold 80-120 FPM face velocity at the sash opening; airflow must rise as the sash is opened wider. It applies the formula CFM = sash width x sash height x face velocity and shows the working so you can check each step by hand.
Is the Fume Hood Sash Airflow 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.