This document defines the fan energy index (FEI), an energy efficiency metric for fans first developed by AMCA International. This metric is further defined in the U.S. Department of Energy (DOE) Term Sheet, a document approved by the DOE that resulted from public negotiations on what a DOE-fan-efficiency regulation would contain. The FEI is a ratio of the actual fan efficiency to a baseline fan efficiency, both calculated at a given airflow and pressure point. Since these efficiencies are each calculated at the same airflow and pressure, FEI is also defined as the ratio of the baseline electrical power to the actual electrical power of a fan.

The FEI was designed to encourage responsible application of fans and drive significant and quantifiable energy savings through energy codes, utility rebate programs and federal regulations. This is accomplished by establishing the minimum fan efficiency or maximum fan input power at design airflow and pressure.