Inline Duct Booster Fan Calculator
Size an inline booster fan for extra duct run pressure loss.
Enter your values
Enter the design airflow in CFM.
Enter the existing system static in in wc.
Enter the added duct run static in in wc.
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.
- Booster fan duty point
- 150 CFM @ 0.7 in wc
- Added static from booster run
- 0.4 in wc
- Recommendation
- Select a booster fan whose curve meets or exceeds this point at design CFM
Quick answer
A booster fan should be sized to deliver the design CFM against the additional pressure drop of the extended or restrictive duct run, on top of existing static.
Booster duty = CFM at (existing SP + added run SP)
At a glance
| What it does | Size an inline booster fan for extra duct run pressure loss. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Design airflow, Existing system static, Added duct run static |
| Main output | Booster fan duty point |
| Formula | Booster duty = CFM at (existing SP + added run SP) |
| Cost | Free — no sign-up, no download |
How to use the Inline Duct Booster Fan Calculator
- 1Enter the design CFM required at the register or outlet.
- 2Enter the existing system static pressure and the additional pressure loss from the extended or restrictive run.
- 3Select a booster fan whose performance curve delivers the design CFM at the combined static pressure.
Inputs explained
- Design airflow(CFM)
- Enter the design airflow in CFM.
- Existing system static(in wc)
- Enter the existing system static in in wc.
- Added duct run static(in wc)
- Enter the added duct run static in in wc.
Worked example
Using the values the calculator loads with:
Inputs
- Design airflow150 CFM
- Existing system static0.3 in wc
- Added duct run static0.4 in wc
Results
- Booster fan duty point150 CFM @ 0.7 in wc
- Added static from booster run0.4 in wc
- RecommendationSelect a booster fan whose curve meets or exceeds this point at design CFM
Frequently asked questions
Where should the booster fan go?
As close to the source (or as centered in the run) as practical, with straight duct both upstream and downstream for best performance.
Can a booster fan replace a bad duct design?
It can compensate for extra length or fittings, but very undersized ducts should still be corrected where possible.
What do I need to enter into the Inline Duct Booster Fan Calculator?
Just 3 values: design airflow, existing system static, added duct run static. 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 Inline Duct Booster Fan Calculator work out the answer?
A booster fan should be sized to deliver the design CFM against the additional pressure drop of the extended or restrictive duct run, on top of existing static. It applies the formula Booster duty = CFM at (existing SP + added run SP) and shows the working so you can check each step by hand.
Is the Inline Duct Booster Fan 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.