About this calculator
This calculator determines the Fan Energy Index (FEI) per AMCA Standard 208. FEI compares actual fan power to a reference fan at the same duty point — a value of 1.0 or higher indicates the fan meets the minimum efficiency standard. Use it to verify code compliance for ASHRAE 90.1 and Title 24, which require FEI ≥ 1.0 for most fan applications (0.95 for variable-air-volume fans). Choose the fan airflow type to set which minimum the result is checked against. Drive losses come from the Drive Type selection.
Use when You need to evaluate fan energy performance per AMCA 208 standard.
Formula FEI = Reference Fan Power ÷ Actual Fan Power
Variables
CFM Airflow in cubic feet per minuteStatic Pressure Fan total pressure in in. w.c. (or fan static pressure with a 0.60 reference fan efficiency)BHP Brake horsepowerAir Density Air density in lb/ft³ (default 0.075)Reference Fan Efficiency (η₀) AMCA 208 reference fan efficiency — 0.66 on a total-pressure basis (default), 0.60 on a static-pressure basisDrive Type Direct drive or belt driveFan Airflow Constant volume (passes at FEI ≥ 1.00) or variable air volume (passes at FEI ≥ 0.95)
CFM
Fan airflow in cubic feet per minute
Static Pressure (in. w.c.)
Fan total pressure, or static pressure with a 0.60 reference efficiency
BHP
Brake horsepower at operating point
Air Density (lb/ft³)
Air density (standard = 0.075 lb/ft³)
Reference Fan Efficiency (η₀)
AMCA 208 reference fan efficiency — 0.66 total-pressure basis, 0.60 static
Drive Type
Fan Airflow
FEI —
Status —
Reference Power (kW) —
Actual Power (kW) —

What is Fan Energy Index (FEI)?

Fan Energy Index (FEI) is a metric defined by AMCA Standard 208 that compares a fan's actual wire-to-air power consumption to a standardized reference fan operating at the same airflow and pressure. An FEI of 1.0 or higher means the fan is at least as efficient as the reference; values below 1.0 indicate the fan does not meet the minimum efficiency threshold. FEI is calculated as: FEI = Reference Fan Electrical Power ÷ Actual Fan Electrical Power. FEI replaced the older Fan Efficiency Grade (FEG) metric and is now required for code compliance. ASHRAE Standard 90.1 Section 6.5.3 and the International Energy Conservation Code (IECC) require FEI of 1.0 or greater for most fan applications above 1 HP (0.95 for variable-air-volume fans). California Title 24 has the same requirement. FEI accounts for the entire drive system including motor and drive losses, making it a more complete measure of installed fan efficiency than fan-only metrics.

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