VFD Speed vs Power Savings Calculator
Power reduction from slowing a fan with a VFD.
Enter your values
ⓘ Live results
Results
- New power draw
- 5.12 kW
- Power saved
- 4.88 kW
- Percent saved
- 48.8%
- New airflow (approx)
- 80% of full CFM
Quick answer
Fan power drops with the cube of speed reduction, so even small speed cuts on a VFD save significant energy.
P2 = P1 x (N2/N1)^3
How to use the VFD Speed vs Power Savings Calculator
- 1Enter the fan's power draw at full speed.
- 2Enter the reduced VFD speed as a percent of full speed.
- 3Read the new power draw and percent saved from the cube-law relationship.
Worked example
Using the values the calculator loads with:
Inputs
- Full-speed power10 kW
- New speed80 % of full speed
Results
- New power draw5.12 kW
- Power saved4.88 kW
- Percent saved48.8%
- New airflow (approx)80% of full CFM
Frequently asked questions
Is this exact for all fans?
It is a good estimate for centrifugal and axial fans in typical duct systems, ignoring drive and motor efficiency changes at part load.
Why do VFDs save so much?
Because power falls with the cube of speed, a 20% speed cut can save roughly 50% of the fan's energy.
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.