Short answer: Under Commission Regulation (EU) 2024/1834 (applies 24 July 2026, replacing 327/2011), a fan is compliant when corrected efficiency η ≥ minimum threshold ηmin.
Threshold: general fans Pe < 10 kW: ηmin = 4.56·ln(Pe) − 10.5 + N; Pe ≥ 10 kW: ηmin = 1.1·ln(Pe) − 2.6 + N. N is the minimum efficiency grade (axial static 50, total 64; other centrifugal 64/67; cross-flow fixed 21%).
Efficiency: η = Cp · Cc · Cguard · Pu/Pe (Annex III 6.1), Pu = qv·Δp at BEP. The raw test-report efficiency must be multiplied by the correction factors before comparing to ηmin.
Example: a 1.1 kW axial fan, static (A/C), N=50 → ηmin = 4.56·ln(1.1) − 10.5 + 50 = 39.93%; measured 45% → compliant, margin +5.07 percentage points.
Horizontal axis: electric input power Pe (log scale). Vertical: efficiency. Blue curve is the compliance threshold ηmin for the chosen type; the dot is the corrected efficiency η. Above the curve = compliant.
Advanced: efficiency correction factors (Annex III 6.1)
If the "Measured η" above is the raw efficiency (Pu/Pe) from the test report, tick what applies and the calculator returns the corrected η used for the verdict. With nothing ticked, η = measured value.
Why compute the corrected η? The regulation compares against η = Cp·Cc·Cguard·Pu/Pe, not the raw efficiency on the test report. A small conformity-assessed VSD fan can carry a part-load factor Cc above 1.11; a fine non-removable guard carries Cguard up to 1.15. Skip these and a compliant product reads as a failure. That is the key difference from every other tool — this one does that step for you.
The six rules the calculator applies
The power boundary follows the regulation: Pe < 10 kW uses the low-power form, Pe ≥ 10 kW the high-power form; exactly 10 kW takes the latter. Correction-factor values are in the table below.
Minimum efficiency grades N (Annex II Table 1)
| Fan type | A / C static | B / D total |
|---|---|---|
| Axial fans | 50 | 64 |
| Forward curved < 5 kW and backward inclined | 52 | 57 |
| Other centrifugal fans | 64 | 67 |
| Mixed flow fans | 57 + 7·(α − 45)/25 | 67 |
| Jet fans ≥ 750 W (category E) | 50 | |
| Cross flow | no grade — fixed 21 % | |
Classification is by geometry: flow angle α < 20° axial, 20° ≤ α < 70° mixed flow, α ≥ 70° centrifugal; blade angle 0° < β₂ ≤ 50° backward curved, 50° < β₂ ≤ 90° backward inclined, β₂ > 90° forward curved. Modifiers: dual use ×0.9, reversible ×0.85, low noise ×0.9, compounding.
Efficiency correction factors (Annex III 6.1)
| Factor | Value | Applies when |
|---|---|---|
| Cp | 0.9 / 1.0 | 0.9 only for a DC motor rated below 100 V with the AC/DC converter outside the fan; otherwise 1.0 |
| Cc | 1.04 | VSD included in conformity assessment, Pe ≥ 5 kW |
| Cc | 1 + 0.0812·Pe−0.5 | VSD included in conformity assessment, Pe < 5 kW (≈1.115 at 0.5 kW) |
| Cc | 1 | No variable speed drive |
| Cguard | 1.00 → 1.15 | Non-removable guard, by opening e: e>30→1; 20<e≤30→1+(30−e)·0.004; 10<e≤20→1.04+(20−e)·0.0035; 8<e≤10→1.075+(10−e)·0.0375; e≤8→1.15 |
Worked examples you can reproduce
| Duty | N | ηmin | Basis |
|---|---|---|---|
| Axial / A·C / 1.1 kW | 50 | 39.93 % | 4.56·ln(1.1) − 10.5 + 50 |
| Axial / A·C / 10 kW | 50 | 49.93 % | high-power form 1.1·ln(10) − 2.6 + 50 |
| Axial / A·C / 30 kW / low noise | 45 | 46.14 % | N = 50 × 0.9 |
| Mixed flow / A·C / 3 kW / α = 60° | 61.20 | 55.71 % | N = 57 + 7·(60−45)/25 |
| Other centrifugal / B·D / 4 kW / σ = 0.10 | 67 | 49.50 % | low-σ case 2.95·σ + 0.2 |
| Jet / E / 2 kW | 50 | 33.82 % | 7.32·ln(2) − 21.25 + 50 |
| Cross flow / B·D / any power | — | 21.00 % | fixed requirement |
These values are produced live by the calculator and can be checked one by one. Full regulation walkthrough: ErP 2026 fan compliance explained.
Related LONGWELL product categories
Related resources
FAQ
Which version of the regulation does this use?
Which number goes in "Measured η"?
Why does adding a VSD raise the efficiency?
Can LONGWELL supply the duty-point data these calculations need?
Does passing here mean the fan is compliant?
Need a duty-point compliance check or a replacement model?
Send the current model, airflow, static pressure, voltage, control method, mounting and annual volume, and LONGWELL can match a suitable platform and supply BEP duty-point data and curves.
Email sales@longwellfans.comRead the full guideSource and disclaimer
Commission Regulation (EU) 2024/1834 of 3 July 2024, Annex II point 1 (with Table 1) and Annex III 6.1. Full text: EUR-Lex, CELEX 32024R1834.
This calculator implements the published formulas to estimate the compliance threshold; it does not replace a test report, a harmonised standard or a conformity assessment. Fan classification, correction-factor values and declared values remain the manufacturer's responsibility under Article 4.