Series Fans Pressure Calculator
Combined static pressure of identical fans in series.
Enter your values
Enter the number of fans in series you are working with.
Enter the pressure per fan alone in in wc.
Enter the interaction derate in %.
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.
- Ideal combined pressure
- 3 in wc
- Realistic combined pressure
- 2.7 in wc
- Loss to interaction
- 0.3 in wc
Quick answer
Ideal series pressure is the sum of each fan's pressure at a given flow, but real systems typically achieve 85-95% of that sum due to inlet turbulence between stages.
SP_combined = n x SP_single x derate
At a glance
| What it does | Combined static pressure of identical fans in series. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Number of fans in series, Pressure per fan alone, Interaction derate |
| Main output | Ideal combined pressure |
| Formula | SP_combined = n x SP_single x derate |
| Cost | Free — no sign-up, no download |
How to use the Series Fans Pressure Calculator
- 1Enter the number of identical fans staged in series and each one's pressure at the shared flow rate.
- 2Apply an interaction derate for turbulence between stages (typically 85-95%).
- 3Use the realistic combined pressure to check the system can be overcome.
Inputs explained
- Number of fans in series
- Enter the number of fans in series you are working with.
- Pressure per fan alone(in wc)
- Enter the pressure per fan alone in in wc.
- Interaction derate(%)
- Enter the interaction derate in %.
Worked example
Using the values the calculator loads with:
Inputs
- Number of fans in series2
- Pressure per fan alone1.5 in wc
- Interaction derate90 %
Results
- Ideal combined pressure3 in wc
- Realistic combined pressure2.7 in wc
- Loss to interaction0.3 in wc
Frequently asked questions
Why stage fans in series instead of one bigger fan?
Series staging (like inline duct boosters) can be a simpler retrofit than replacing a single fan with a larger unit.
Does spacing between fans matter?
Yes — more distance between stages reduces turbulent interaction and improves the combined pressure.
What do I need to enter into the Series Fans Pressure Calculator?
Just 3 values: number of fans in series, pressure per fan alone, interaction derate. 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 Series Fans Pressure Calculator work out the answer?
Ideal series pressure is the sum of each fan's pressure at a given flow, but real systems typically achieve 85-95% of that sum due to inlet turbulence between stages. It applies the formula SP_combined = n x SP_single x derate and shows the working so you can check each step by hand.
Is the Series Fans Pressure 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.