Fan Efficiency Calculator
Total fan efficiency from airflow, pressure and power.
Enter your values
ⓘ Live results
Results
- Fan efficiency
- 40.2%
- Air power
- 0.378 HP
- Specific fan power
- 0.74 W per L/s
- Watts per CFM
- 0.35
- Rating
- Poor — check duct restriction
Quick answer
Fan efficiency is air power divided by shaft or input power; good HVAC fans land between 55% and 75%.
eff = CFM x in wc / (6356 x HP)
How to use the Fan Efficiency Calculator
- 1Measure airflow and total pressure rise across the fan.
- 2Read input watts at the plug or from the VFD.
- 3Compare watts per CFM — under 0.5 is good for a residential ECM blower.
Worked example
Using the values the calculator loads with:
Inputs
- Airflow2000 CFM
- Total pressure1.2 in wc
- Input power700 W
Results
- Fan efficiency40.2%
- Air power0.378 HP
- Specific fan power0.74 W per L/s
- Watts per CFM0.35
- RatingPoor — check duct restriction
Frequently asked questions
Why is my efficiency low?
Usually excessive system static, a dirty wheel, or a fan operating far off its best efficiency point.
What is specific fan power?
Watts per litre per second — European standards often cap it at 1.6 W/(L/s) for balanced systems.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.