Use matched test data and rating inputs to calculate fan energy index or efficiency grade and criterion margins.
Concepts behind this calculation
Calculate a complete AMCA 214-21 fan energy index reference chain or an AMCA 205-19 table-based fan efficiency grade, with explicit test and power boundaries.
FEI compares the reference electrical input with the actual electrical input at one fan duty point. Airflow, pressure, density and power must describe that same point. The fan type and actual test configuration determine whether static or total pressure belongs in the comparison. An FEI above one means the entered fan uses less electrical input than the modeled reference at that point; it is not an annual energy estimate.
FEG classifies peak fan-only total efficiency with a diameter-dependent band. It uses a different power boundary and operating basis from FEI. The bare-shaft FEI route also has a specific purpose: it constructs default drive and motor inputs for a qualifying bare-shaft configuration. Applying that default to a supplied motor or VFD package would replace the relevant electrical evidence with a different model.
How to use this calculator
Choose Rating method and complete Fan, test and calculation-source reference with the appropriate power boundary.
For FEI, select Fan type and Actual test configuration; enter Tested duty-point airflow, matching Fan pressure, Air density and Selected project minimum FEI.
Enter Tested or rated electrical input, or use Tested bare-shaft power and Bare-shaft default transmission only when that route applies.
For FEG, enter Actual impeller tip diameter, Tested peak total fan efficiency, Shaft power at the peak test, both speed limits and Peak test application category. Review scope and band support.
Calculation method and applicability
FEI=reference electrical input/actual electrical input. I-P reference shaft=(Q+250)×(P+0.40ρ/0.075)/(6343.3η0), η0=0.60 static or0.66 total; apply reference V-belt and motor curves. FEG uses the 205-19 Annex A continuous diameter equation, capped at 1,016 mm, and exact geometric band multipliers.
Q = tested duty airflow (CFM); P = compatible fan pressure (in. w.g.); ρ = duty air density (lb/ft³); η0 = stated reference efficiency. FEI is an electrical-input ratio and FEG is a peak-efficiency grade; neither is a percent efficiency.
Input definitions and units
Rating method
FEI evaluates one duty point using the214-21 I-P chain. FEG evaluates peak fan-only total efficiency using205-19 Annex A. These metrics are distinct. Choices: FEI — tested electrical input; FEI — bare-shaft default drive and motor; FEG — peak total efficiency.
Fan, test and calculation-source reference
Required: exact model, test/report source, selected standard edition, duty or peak RPM, accessories and power boundary. For FEI state test configuration and electrical input boundary; for FEG state peak-total-efficiency test method and category. No data are authenticated by this note.
Fan type
Table 7.1 determines allowed test configurations and static/total basis. Jet/circulating thrust conversions, ceiling, cross-flow and air curtains are not implemented. Choices: Centrifugal housed; Radial housed; Centrifugal inline; Centrifugal unhoused; Centrifugal PRV exhaust; Centrifugal PRV supply; Axial inline; Axial panel; Axial PRV; Laboratory exhaust — no induced flow; Laboratory exhaust — induced flow. Applies to Rating method: FEI — tested electrical input or FEI — bare-shaft default drive and motor.
Actual test configuration
A=free inlet/free outlet; B=free inlet/ducted outlet; C=ducted inlet/free outlet; D=ducted inlet/ducted outlet. Select the actual rating test; installed duct appearance alone does not establish the proper basis. Choices: A — free inlet, free outlet; B — free inlet, ducted outlet; C — ducted inlet, free outlet; D — ducted inlet, ducted outlet. Applies to Rating method: FEI — tested electrical input or FEI — bare-shaft default drive and motor.
Tested duty-point airflow (CFM)
Use the tested or source-rated single-fan point. Arrays and parallel assemblies cannot be treated as independent single-fan FEIs. Applies to Rating method: FEI — tested electrical input or FEI — bare-shaft default drive and motor.
Fan pressure at the same duty point (in. w.g.)
Enter static or total pressure as required by the selected fan/test pair. The result reports the derived basis. No automatic conversion or density normalization of this pressure. Applies to Rating method: FEI — tested electrical input or FEI — bare-shaft default drive and motor.
Air density at the tested duty point (lbm/ft³)
214-21 I-P standard density is0.075. Actual density enters the reference pressure offset; it does not multiply the whole measured pressure. Applies to Rating method: FEI — tested electrical input or FEI — bare-shaft default drive and motor.
Selected project minimum FEI (FEI)
Explicit project comparison, not a built-in energy-code rule. Determine the applicable threshold and exemptions separately. Applies to Rating method: FEI — tested electrical input or FEI — bare-shaft default drive and motor.
Tested or rated electrical input (kW)
Use input at the applicable mains boundary, including VFD input where fitted; not motor output, shaft hp, nominal motor capacity or current alone. The rating method/test must be documented. Applies to Rating method: FEI — tested electrical input.
Tested bare-shaft power (hp)
214-21 Section 6.3 only: bare-shaft sales configurations or qualifying non-electric driver. Default motor/drive is not a model of a supplied motor/VFD package. Applies to Rating method: FEI — bare-shaft default drive and motor.
Bare-shaft default transmission
Use unity only for a fan that can have direct drive only. All other eligible bare-shaft configurations use the standard default V-belt curve. This is not a menu for a supplied synchronous drive. Choices: Direct-drive-only bare shaft; Other bare shaft — default V-belt. Applies to Rating method: FEI — bare-shaft default drive and motor.
Actual impeller tip diameter (in.)
205-19 I-P scope starts at 5 in; use the largest circle swept by blade tips. Curve saturates at 40 in. Continuous equation is used; no nominal R40 size rounding. Applies to Rating method: FEG — peak total efficiency.
Tested peak total fan efficiency (%)
Fan-only peak total efficiency excluding drive losses, at the documented test speed/category. A single arbitrary duty-point wire-to-air efficiency is not a peak total efficiency. Applies to Rating method: FEG — peak total efficiency.
Shaft power at the peak test (hp)
Scope gate: at least1 hp in this I-P implementation. This is not nameplate motor capacity and is not used to derive a peak efficiency. Applies to Rating method: FEG — peak total efficiency.
Peak-efficiency test speed (RPM)
205-19 requires the speed used to establish the peak to be below maximum fan design speed. Applies to Rating method: FEG — peak total efficiency.
Maximum fan design speed (RPM)
Source-supported mechanical design limit. A peak test at or above this value is outside the implemented classification contract. Applies to Rating method: FEG — peak total efficiency.
Peak test application category
Report A/B/C/D with the classification. The source test method must establish total efficiency regardless of duct configuration. Choices: A — no inlet or outlet ducts; B — outlet duct only; C — inlet duct only; D — inlet and outlet ducts. Applies to Rating method: FEG — peak total efficiency.
How to interpret the result
For FEI, retain the reported pressure basis, reference-power chain and comparison with Selected project minimum FEI. For FEG, retain the diameter treatment and exact band bounds; an out-of-table result does not justify inventing the next grade.
Worked examples
FEI — tested electrical input
Inputs: Published illustrative one-fan point: 50, 000 CFM, 6 in. w.g.static, 0.075 lbm/ft³, 59.6 kW actual input; centrifugal unhoused configurationA, selected minimum 1.00. Recalculate the complete reference chain using 214-21 I-P.
Result: FEI 1.158, with 9.416413 kW headroom at selected minimum 1.00. The208-18 illustrative table rounds FEI to 1.16 but prints reference 69.1 kW, which does not exactly reproduce; the difference is retained.
FEI — bare-shaft default drive and motor
Inputs: Constructed full default-drive reconstruction: 50, 000 CFM, 6 in. w.g.static at 0.075 lbm/ft³, centrifugal unhousedA, bare shaft 72.8 hp, not direct-drive-only. No supplied motor/controller is modeled.
Result: 1.158 FEIs and 9.435191 kW headroom against selected minimum 1.00. This explicitly bare-shaft model is not a certified driven fan or a selected motor/VFD curve.
FEG — peak total efficiency
Inputs: AMCA 205-19 example: 500 mm actual impeller diameter (19.68503937 in), tested 79% peak total efficiency at 1,800 RPM, application category C. Example scope-support shaft 1 hp and design maximum2, 000 RPM are constructed additions, not values printed in the source example.
Calculation: Annex A exact constants give FEG 85 upper81.470402% and lower76.913019% at 500 mm; 79% falls inside the lower-exclusive, upper-inclusive band.
Result: FEG 85. This matches the source grade and its 81.5/76.9 one-decimal boundaries. Source drive/test validity must be established independently.
Assumptions and limits
FEI and FEG are distinct metrics; neither replaces equipment selection, annual energy, drive efficiency or an adopted-code assessment. No jurisdictional threshold, exemption or current-standard claim is embedded.
FEI covers supported single-fan Table 7.1 configurations only. Fan arrays, parallel/series combinations, embedded-equipment/system-effect corrections, jet/circulating thrust conversion and untested rating interpolation are outside this page.
Electrical input must include the relevant mains/controller boundary at the same duty point. Motor nameplate capacity, shaft power or current alone are not measured electrical input.
The bare-shaft 214-21 Section6.3 default route is implemented. Supplied regulated motors, selected motor/VFD polynomial models and separately tested power-drive reconstruction are not silently treated as that default.
This I-P implementation uses6343.3 and native 250 hp motor-branch boundaries. The source also prints 185 kW, which is not exactly250 hp×0.7457; unit-system profiles can differ near the threshold. No efficiency is clipped if the mathematical chain is nonphysical.
FEG scope uses I-P: 5 in and 1 hp; rounded SI counterparts 125 mm/750 W are not treated as exact equivalences. Peak total efficiency must be supported by applicable test methods. Scope/example additions are explicitly constructed.
205-19 Annex A TableA.2 labels one grade FEG 57, while Figure 3b calls it FEG 56. The inspected tables do not define the figure’sFEG90. This page preserves the table label and withholds assignment above the highest tabulated band.
208-18 illustrative source tables do not reproduce every printed FEI or reference-power value from the inspected chain. Specific mismatches are retained in the batch evidence; example data are not silently altered to match.
FAQs
Can I enter motor nameplate horsepower as FEI electrical input?
Nameplate capacity does not state the electrical power consumed at the duty point. Use the matching tested or rated mains input, including the relevant controller boundary, or the qualifying bare-shaft method with actual shaft power.
Can a good FEI establish the fan’s FEG?
No. FEG needs tested peak total fan-only efficiency, impeller tip diameter and its own test-speed and scope evidence. A single duty-point electrical ratio cannot establish those inputs.
ANSI/AMCA 205-19 efficiency classificationPublicly accessible without login at inspection. Scope, Section 6 peak example and Annex A exact curve/bands;Table/figure discrepancies explicitly retained. Full standard text is not redistributed.
ANSI/AMCA 208-18 FEI definition and examplesHistorical definition and illustrative one-fanAnnex Ccomparison. Example column differences are documented, not treated as exact214-21validation.
