FEI stands for Fan Energy Index and can be determined according to the American National Standard AMCA 208-18 introduced in January 2018.
According to DIN EN ISO 12759, fans can be classified by means of the FEG (Fan Efficiency Grade) index. However, FEG only applies to fans with an exposed shaft, i.e. without a motor. The FEI, on the other hand, is based on the electrical input power of a complete fan and considers the losses of all components of the fan and their effect on energy efficiency. The FEI represents a complete energy efficiency metric for fans and provides a standardized as well as consistent basis for comparing the energy efficiency of fans of different types and sizes at a given operating point. Regulatory authorities use the FEI to monitor and control fan energy efficiency requirements