Fan Efficiency Grade (FEG) calculator
Enter the impeller diameter and the fan's peak total efficiency to get its AMCA 205-10 Fan Efficiency Grade — the grade band boundaries at that size, and a chart plotting all FEG curves against fan size with your fan marked on it.
How this calculator works
AMCA 205-10, "Energy Efficiency Classification for Fans", defines Fan Efficiency Grades (FEG) as bands of peak total efficiency that shift with fan size — a small fan is held to a lower bar than a large one, because small fans are aerodynamically harder to make efficient. Annex A gives the exact formula for the FEG85 upper-limit efficiency curve as a function of impeller diameter:
η85D_upp(D) = k0 + √[81 + D/k1 − (D/k2)²] − 112·e^(−D/k3)
k1 = 793.75/15² k2 = 1270/15 k3 = 113.92 D0 = 1016 mm
k0 = 10^(1+37/40) − 15 + 112·e^(−D0/k3)
Every other grade's upper limit at that same size is FEG85's curve multiplied by a fixed constant from Annex A Table A.2 (a geometric series, quotient 10^−1/40) — FEG80 is ×0.94406088, FEG75 is ×0.89125094, and so on down to FEG50. A fan belongs to the highest grade whose upper limit is still ≥ its actual peak efficiency. Per the standard's Note 5, the curves flatten out above 1016 mm — larger fans use the same limits as a 1016 mm fan.
This was verified against AMCA 205's own worked example: a 500 mm fan at 79% efficiency is stated to fall in FEG85, bounded by an 81.5% upper limit and a 76.9% lower limit — this calculator reproduces 81.47% and 76.91% for that exact input.
If you don't already have a peak efficiency figure, switch "Efficiency input" to calculate it from airflow, total pressure and shaft power — the standard definition of fan total efficiency, exact mechanics rather than an AMCA-specific formula:
η = Ho / Hsh × 100 Ho = Q · Pt / 3600 [W, Q in m³/h, Pt in Pa]
Ho is the fan's air (aerodynamic) power and Hsh is the shaft power it's actually drawing — both at the same operating point.
One honesty note: AMCA 205's Annex A table (10 grades, FEG85 down to FEG50) and its own Figure 3a chart don't quite agree with each other. The table's eighth grade rounds to 56.23% but is labelled "FEG57"; the figure labels that same curve "FEG56" (the more correct rounding). The figure also shows an FEG90 curve above FEG85 that Annex A never defines a formula for. This calculator uses "FEG56" to match the figure and the correct rounding, and does not offer an FEG90 grade — inventing a constant for it would mean fabricating a number the standard itself doesn't provide.
This page checks one fan at a time. CloudAir's selection programs can surface efficiency classification for every fan in your catalogue automatically. See how CloudAir handles it →