Damper Authority Calculator
Control authority of a modulating damper in a duct system.
Enter your values
Enter the damper pressure drop (wide open) in in wc.
Enter the rest-of-system pressure drop 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.
- Damper authority
- 20%
- Rating
- Poor - control will be non-linear, oversized damper
- Total loop pressure drop
- 0.75 in wc
Quick answer
Damper authority equals the damper's own pressure drop divided by the total pressure drop of the damper plus the rest of the system it controls.
Authority = dP_damper / (dP_damper + dP_system)
At a glance
| What it does | Control authority of a modulating damper in a duct system. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Damper pressure drop (wide open), Rest-of-system pressure drop |
| Main output | Damper authority |
| Formula | Authority = dP_damper / (dP_damper + dP_system) |
| Cost | Free — no sign-up, no download |
How to use the Damper Authority Calculator
- 1Enter the damper's pressure drop when fully open at design flow.
- 2Enter the pressure drop of the rest of the branch or system the damper modulates.
- 3Read the damper authority — values above 0.5 give the most linear, stable control.
Inputs explained
- Damper pressure drop (wide open)(in wc)
- Enter the damper pressure drop (wide open) in in wc.
- Rest-of-system pressure drop(in wc)
- Enter the rest-of-system pressure drop in in wc.
Worked example
Using the values the calculator loads with:
Inputs
- Damper pressure drop (wide open)0.15 in wc
- Rest-of-system pressure drop0.6 in wc
Results
- Damper authority20%
- RatingPoor - control will be non-linear, oversized damper
- Total loop pressure drop0.75 in wc
Frequently asked questions
Why is low authority a problem?
A damper with low authority does almost all its work near the closed position, making control jumpy and hard to tune.
How do I increase authority?
Select a smaller, higher-pressure-drop damper, or reduce the rest-of-system resistance.
What do I need to enter into the Damper Authority Calculator?
Just 2 values: damper pressure drop (wide open), rest-of-system pressure drop. 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 Damper Authority Calculator work out the answer?
Damper authority equals the damper's own pressure drop divided by the total pressure drop of the damper plus the rest of the system it controls. It applies the formula Authority = dP_damper / (dP_damper + dP_system) and shows the working so you can check each step by hand.
Is the Damper Authority 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.