• FEG (Fan Efficiency Grade): Measures the fan’s peak total efficiency at a single operational point in the lab, typically adjusted for impeller size.
• FMEG (Fan Motor Efficiency Grade): A wire‑to‑air metric that also considers motor and drive losses—but still based on a single peak efficiency point.

Both metrics fall short because most fans rarely operate at peak lab conditions. FEI, in contrast, is calculated across the entire operating range and at actual duty points, making it a more accurate measure for real-world performance and regulatory compliance