Fan Energy Index (FEI) - HVAC Calculator Toolbox

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.

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 static pressure in inches W.C.BHP Brake horsepowerAir Density Air density in lb/ft³ (default 0.075)Transfer Efficiency Motor/drive transfer efficiency (default 0.66)Drive Type Direct drive or belt drive

CFM

Fan airflow in cubic feet per minute

Static Pressure (in. W.C.)

Fan total static pressure in inches water column

BHP

Brake horsepower at operating point

Air Density (lb/ft³)

Air density (standard = 0.075 lb/ft³)

Transfer Efficiency

Motor to fan power transfer efficiency

Direct drive

Belt drive

Drive Type

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. 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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