Fan Efficiency Explained: ISO 12759, FEG, FMEG and EU Regulation 2024/1834

Fan efficiency is the share of the power that reaches the fan shaft or the electrical terminals that ends up as useful air power. Comparing fans on efficiency saves energy over the fan’s life, because a small difference at 8,000 running hours a year adds up quickly. But efficiency figures are only comparable when they use the same basis. This guide explains the definitions, the classification systems in ISO 12759, and the EU ecodesign rule that changed in July 2026.

Air Power and Total Efficiency

Air power is the useful work done on the air: flow multiplied by fan total pressure. Total efficiency is air power divided by the power at the fan shaft.

Example. A fan delivers 25 m³/s at 800 Pa total pressure and absorbs 26 kW at the shaft. Air power is 25 × 800 = 20 kW. Total efficiency is 20 ÷ 26 = 77%.

Static efficiency uses static pressure in place of total pressure, and it is lower for a fan that discharges freely. Always confirm which basis a claimed efficiency uses.

Where the Losses Go

Between the electrical supply and the air, power is lost in several places: motor losses, drive losses if a belt or coupling is used, control losses if a variable-speed drive is fitted, bearing losses, and aerodynamic losses in the fan itself, including some that leave as noise. A fan’s efficiency describes the last of these, while an assembly’s overall efficiency includes them all. This is why “fan efficiency” and “fan plus motor efficiency” are different numbers.

Why Efficiency Matters: A Simple Calculation

Using the example above, a fan with 80% total efficiency would absorb 20 ÷ 0.80 = 25 kW, compared with 26 kW at 77%. That one kilowatt saved runs for the year:

Saving ≈ 1 kW × 8,000 hours ≈ 7,800 kWh per year

For a plant with many fans, or with a fan running continuously over a decade, the efficiency difference often outweighs the purchase price difference.

ISO 12759: FEG and FMEG

ISO 12759 provides a worldwide way to classify fan efficiency, so legislators and industry can set targets on a common basis. It has two schemes.

• FEG, fan efficiency grade. Applies to bare-shaft fans, meaning the fan without its motor or drive. It is determined at the fan’s peak total efficiency point, and the grade bands rise with impeller diameter. It is used widely in North America and is harmonised with AMCA 205.
• FMEG, fan motor efficiency grade. Applies to the complete assembly with motor, drive, and any variable-speed drive. It captures losses in each part and from poor matching of components. It is the main method in Europe.

The efficiency required for a given FMEG depends on electrical power and fan type. For axial fans above 10 kW, the minimum peak efficiency in the ISO 12759 scheme has the form 0.78 × ln(Pe) − 1.88 + N, where Pe is electrical input power in kW and N is the grade number. A higher N means a higher required efficiency, and the requirement rises slowly with size.

ISO 12759 is not directly applicable to every fan. The standard’s summary lists exclusions including smoke fans, explosion-proof fans, and jet fans, among others.

EU Ecodesign: From 327/2011 to 2024/1834

The EU regulates fans driven by motors with an electric input power from 125 W to 500 kW. Regulation (EU) 327/2011 set minimum efficiency using the ISO 12759 approach. Regulation (EU) 2024/1834 replaced it, with effect from 24 July 2026.

The new regulation applies to fans with an electric input power between 125 W and 500 kW at their best efficiency point, including where they are integrated into other products. Compared with the old rule, it brings stricter performance requirements, new repairability requirements, and requirements to publish fan performance at different loads and speeds. Parts of the earlier regulation continue to apply for fans integrated into other products and for spare-part fans until 24 July 2037. Fan impellers mounted on a motor shaft solely to cool that motor are outside its scope.

Two points follow. First, many older web pages, datasheets, and tenders still cite 327/2011, so check the date of any efficiency claim. Second, this is an EU regulation. It does not automatically apply in every market where we supply, but it is a widely used reference, and many buyers and consultants specify to it.

How to Compare Fans Fairly

1. Same basis. Total or static efficiency, bare shaft or with motor.
2. Same point. Peak efficiency versus efficiency at your duty point. A fan that peaks well but runs far from its peak may perform poorly in your system.
3. Same conditions. Air density and speed.
4. Tested data. Ratings from tests to ISO 5801 or AMCA 210, not estimates. See fan performance testing.
5. Part-load behaviour. If the fan runs at reduced flow much of the time, part-load efficiency and control method matter as much as peak efficiency. See adjustable pitch versus VFD control.

The Motor Side

Motor efficiency classes are defined separately, in IEC 60034-30-1, which grades motors into IE classes, with higher numbers meaning higher efficiency. Fan manufacturers commonly fit high-efficiency motors of IE3 class or better, and IE3 or IE4 is increasingly the expectation on new equipment. A high-efficiency motor helps, but the fan’s aerodynamic efficiency and the system match usually matter more.

Beyond the Fan: The System

The most efficient fan in a poorly designed system is still wasteful. Oversized margins, restrictive inlet and outlet arrangements, sharp bends close to the fan, and clogged filters all raise the resistance the fan must overcome. Reducing system resistance often saves more energy than upgrading the fan.

Checklist for Specifying Efficiency

1. State the pressure basis and the efficiency basis.
2. Specify the duty point and the operating range, not only the peak.
3. Ask for test-based performance data.
4. Ask about part-load performance and control.
5. State the motor efficiency class required.
6. Check which regulation or reference standard your client requires.

Ask for Test-Based Efficiency at Your Duty Point

Send your duty and operating hours, and we’ll provide performance data and an efficiency comparison for your application. Contact us for a free quote.

Frequently Asked Questions