Duct Velocity Noise Calculator
Check duct velocity against noise limits.
Enter your values
Enter the airflow in CFM.
Enter the duct diameter in in.
Choose one of: Occupied space branch, Trunk near equipment room, Mechanical room / exposed.
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.
- Velocity
- 1,100 FPM
- Recommended limit for this location
- 700 FPM
- Status
- Exceeds recommended limit — increase duct size
Quick answer
Recommended maximum duct velocities to avoid noticeable noise range from about 600 FPM near registers to 1500+ FPM in mechanical room trunks.
Velocity = CFM / cross-section area
At a glance
| What it does | Check duct velocity against noise limits. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Airflow, Duct diameter, Duct location |
| Main output | Velocity |
| Formula | Velocity = CFM / cross-section area |
| Cost | Free — no sign-up, no download |
How to use the Duct Velocity Noise Calculator
- 1Enter the duct's airflow and diameter to calculate velocity.
- 2Select where the duct segment is located, since noise tolerance differs by room type.
- 3Compare the calculated velocity against the recommended limit for that location.
Inputs explained
- Airflow(CFM)
- Enter the airflow in CFM.
- Duct diameter(in)
- Enter the duct diameter in in.
- Duct location
- Choose one of: Occupied space branch, Trunk near equipment room, Mechanical room / exposed.
Worked example
Using the values the calculator loads with:
Inputs
- Airflow600 CFM
- Duct diameter10 in
- Duct locationOccupied space branch
Results
- Velocity1,100 FPM
- Recommended limit for this location700 FPM
- StatusExceeds recommended limit — increase duct size
Frequently asked questions
Why do limits vary by location?
Occupied rooms are far more sensitive to airflow noise than a mechanical room or attic, so limits are much stricter there.
What if velocity is too high?
Increase the duct diameter, which lowers velocity for the same CFM and quiets the run.
What do I need to enter into the Duct Velocity Noise Calculator?
Just 3 values: airflow, duct diameter, duct location. 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 Duct Velocity Noise Calculator work out the answer?
Recommended maximum duct velocities to avoid noticeable noise range from about 600 FPM near registers to 1500+ FPM in mechanical room trunks. It applies the formula Velocity = CFM / cross-section area and shows the working so you can check each step by hand.
Is the Duct Velocity Noise 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.