Energy Efficiency Class A in Circulation Pumps: What It Means in Practice
Energy efficiency class A for circulation pumps: what does it mean in practice
When you look at the range of circulation pumps for your heating system or boiler, you will come across the designation "class A" or "EEI ≤ 0,23". For some, this may sound like a marketing slogan with little real content. In reality, it is a very specific technical parameter that directly affects how much electricity your pump consumes in a year, and thus how much you will pay extra – or save – throughout its entire lifetime. In this article, we will explain what class A for circulation pumps really means, how it is measured, why it became mandatory, and what it means for the average boiler owner or technician who installs the pump.
Short history: from old three-speed pumps to class A
Until 2013, most circulation pumps in European households were so-called "wet-rotor" construction type with a three-speed switch. These pumps ran practically continuously at constant speeds regardless of the current heat demand. In summer, when the system did not need to circulate anything, the pump still ran at full power. In a mild autumn night, when only 10% of the power was needed, the pump still ran at full speed. Result? The average consumption of such a pump ranged between 60 and 100 W, which amounts to 525 to 875 kWh per year. At an electricity price of around 0.20 €/kWh, this means 105 to 175 € per year – just for one pump.
The European Union realized that circulation pumps throughout Europe consume an enormous amount of electricity – estimated at up to 50 billion kWh per year. Therefore, Commission Regulation (EU) No 641/2009 and its amendment No 622/2012 set mandatory requirements for pumps with an Energy Efficiency Index (EEI) ≤ 0.23 for pumps sold on the EU market. This limit came into force on August 1, 2015, for standalone pumps and on January 1, 2013, for pumps built into boilers. Precisely those pumps meeting this limit receive the designation "class A".
What exactly is EEI and how is it calculated
EEI – Energy Efficiency Index – is a dimensionless number that expresses how much power the pump draws from the grid compared to a reference power calculated according to the EN 16297 standard. The lower the number, the more efficient the pump. Class A means EEI ≤ 0.23. The best pumps on the market today achieve EEI around 0.15 to 0.18.
The calculation of EEI is based on a so-called reference load profile. The pump is tested in various operating points – not only at maximum power, but also at 25 %, 50 % and 75 % of the nominal value. This corresponds to real operation: a pump in a family house boiler usually does not run at full power most of the year. It runs at partial load and it is precisely in this operating mode that the real difference between an old single-speed pump and a modern EC (electronically commutated) pump with a permanent magnet becomes apparent.
The key technical change compared to old pumps is the motor. Traditional pumps used an asynchronous motor with fixed speeds. Class A pumps use an EC motor (also known as a permanent magnet motor, or BLDC – Brushless DC). This motor can smoothly adjust the speed depending on the current system demand. Integrated electronics measuring differential pressure or temperature decide when to add or reduce power. The result is consumption ranging from 3 to 30 W depending on the load, compared to constant 60–100 W in old models.
Which specific class A pumps are used in ATTACK boilers
If you have a boiler from the brand ATTACK (whether it is a pellet, wood, or combined boiler), the pump is one of the key components that directly affects the efficiency of the entire system. ATTACK boilers either come with an integrated pump or the pump is mounted in an external circulation loop. In both cases, it has been mandatory since 2013 that the pumps installed in the boilers are of class A.
In practice, we encounter two main sizes in ATTACK boilers: 130 mm (the distance between the thread connections, so-called construction length) and 180 mm. Whether the 130 mm or 180 mm size fits your boiler is discussed in more detail in the article 130 mm pump size vs 180 mm: which fits my boiler. Here, we will focus on which specific class A pumps are available for these boilers.
For the 130 mm construction length, a typical representative is the ATTACK Heating circulation pump 25/6, 130 mm, class A. This pump is universal and is suitable not only as a spare part but also for new installations where space is limited. For the larger 180 mm construction length, there is the ATTACK Heating circulation pump PR 25/6, 180 mm, class A. Both types meet the requirements of EEI ≤ 0.23 and are therefore full-fledged class A pumps.
Alongside these universal pumps, there are also direct spare parts with proven mechanics from the manufacturer WILO. ATTACK Pump WILO Yonos PARA RS25/6, 130 mm and ATTACK Pump Yonos PARA RS25/6 RKC, 180 mm are specifically designed as spare parts for ATTACK boilers and their use ensures that you will not encounter compatibility issues or the need for additional parameter settings.
Parameters 25/6: what the pump designation itself means
Class A is important, but it alone does not tell you everything about whether a given pump is suitable for your system. The second key parameter is the designation "25/6". The first number – 25 – indicates the maximum pipe diameter (DN 25, i.e., 1 inch G1). The second number – 6 – indicates the maximum pumping head in meters of water column (mH₂O). For more information on how to interpret these numbers for your specific system, see the article Pump parameters 25/6: what the numbers mean and how to read them.
For a typical family house with an area up to 200 m² and a standard hot water radiator system, the parameters 25/6 are completely sufficient. A DN 25 pump with a head of 6 m is capable of covering a flow rate in the range of 0 to approximately 3.5 m³/h, which is enough for a circuit with a power demand up to 20–25 kW. In larger systems or in floor heating with long circuits, it is necessary to perform a hydraulic calculation to determine whether these parameters are sufficient – but that is a topic for another article.
Operating modes of class A pumps: how to set them correctly
One of the most common mistakes technicians encounter in the field is when a customer has a new class A pump but runs it in an unsuitable mode. Modern EC pumps typically offer several operating modes. Understanding these modes is key to actually achieving energy class A in practice.
Constant pressure mode (CP – Constant Pressure)
In this mode, the pump maintains a constant differential pressure regardless of the flow. When thermostatic heads on radiators close and the flow decreases, the pump reduces its speed to keep the pressure the same. This mode is suitable for systems with thermostatic valves, where the hydraulic characteristics of the system change. It is the most commonly used and recommended mode for most modern heating systems in family homes.
Proportional pressure mode (PP – Proportional Pressure)
The differential pressure changes proportionally with the flow. At zero flow, the pressure is minimal, and at maximum flow, it is maximum. This mode is suitable for systems with long distribution lines and signs of hydraulic instability – the pump operates most energy-efficiently in this mode and, on average, achieves the lowest consumption. For most ATTACK boilers with a standard distribution system in a family home, this mode is ideal.
Constant speed mode (CN – Constant Speed)
The pump runs at fixed speeds – practically the same as an old three-speed pump. In this mode, the advantages of the EC motor are not utilized, and the consumption is much higher than in automatic modes. This mode is used only exceptionally, for example, during system flushing or diagnostics.
Actual electricity consumption: real numbers from practice
Theory is nice, but customers are interested in specific numbers. From my own experience during installation and warranty repairs of ATTACK boilers, I can cite several typical scenarios:
Scenario 1: Family house 120 m², radiator heating, original three-speed pump
The pump was running on the 2nd speed, power consumption measured by a wattmeter: 68 W. The heating season lasts about 200 days × 18 hours of boiler operation = 3,600 hours. Annual consumption: 68 W × 3,600 h = 244.8 kWh. In addition, the pump was also running in summer during hot water preparation (another 4,000 hours at a lower power). Total: approximately 400–450 kWh per year.
After replacement with a class A pump (WILO Yonos PARA RS25/6) in PP mode: consumption measured by a wattmeter at a typical load point: 8–22 W depending on current load. Annual actual consumption after replacement: approx. 55–80 kWh. Annual savings: 350–370 kWh, which at a price of 0.22 €/kWh represents 77–81 € per year. Return on investment in the new pump (price 80–120 €) within two seasons.
Scenario 2: Older family house 160 m², combined boiler ATTACK, pump on 3rd stage
Technicians were called due to vibrations and noise. The old pump was running at maximum speed, consumption 95 W. The customer had no idea such a pump existed – the boiler was installed 12 years ago. After replacement with ATTACK Pump Yonos PARA RS25/6 RKC, 180 mm in CP mode: quiet operation, consumption 12–18 W, radiators equally warm. The customer was surprised that the system worked better with lower pump output – this is exactly the intention of self-regulation.
Scenario 3: New installation, floor heating + radiators
Mixed system with longer floor heating loops. The original hydraulic calculation assumed a 25/8 pump, but the customer had only a 25/6 available. After setting the class A pump (with smooth regulation) to a higher pressure point and correcting the balancing valves, the system operated correctly. Reason: the old 25/8 on the 2nd stage actually delivered only 5 m Hv, while the new 25/6 in automatic CP/max mode was able to work effectively in the same range, with significantly lower consumption.
EU requirements and legal obligations: what the installer must know
Since 1 January 2013, it has been a legal requirement that every boiler sold in the EU must have an integrated pump with EEI ≤ 0.23. The same obligation applies to separate pumps intended for installation in heating systems since 1 August 2015. This regulation applies to wet-rotor circulation pumps with a power rating up to 2 500 W and a maximum working pressure up to 10 bar.
This brings clear obligations for the installer and technician: if you are replacing a pump in an existing boiler, you cannot legally install a new pump of the old generation (class D, E or F). The only exception is stock purchased before the regulation came into force – but such goods should have been sold out long ago. In practice, this means that any new pump you buy today in a serious e-shop or hardware store must be class A. If someone offers you a "new" pump without class A significantly cheaper, it is either old stock with questionable history or a low-quality product that did not meet certification.
In addition to the energy class, the manufacturer must also state on the pump label: EEI, rated power, hydraulic power, noise level and other parameters. These data are also found in the pump's accompanying documentation and are important for warranty claims or boiler inspections.
Lifespan and pump service of class A
Pumps of class A with EC motor have basically a longer planned lifespan than old asynchronous types. Manufacturers state a lifespan of 15–20 years with proper handling. The main factors that shorten the lifespan are:
- Corrosion and deposits in the system – an old system without regular descaling brings impurities that damage the bearings of the impeller. EC motor handles this better than the old asynchronous motor, but magnetic and abrasive particles are a problem for any type of pump.
- Air in the system – air pockets cause cavitation, which mechanically destroys the blades of the impeller. System venting before the start of the season is a basic and necessary operation.
- Inappropriate water quality – hard water with calcium and magnesium content creates deposits on heat exchangers and inside the pump. The ideal pH for water in the heating circuit is 7–9, hardness up to 2.0 mmol/l.
- Long-term shutdown – pumps that stand for months without movement (summer breaks) can have a seized rotor. Modern EC pumps have an automatic anti-seizure cycle function, but not all cheaper models.
- Operation outside the hydraulic range – if the pump runs for a long time at zero flow (all valves closed), overheating of the electronics can shorten the lifespan of the frequency converter.
About when it is time to replace the pump and what symptoms precede a failure, you will read in the article When to replace the circulation pump in the boiler: symptoms and lifespan and in the article Common failures of circulation pumps in ATTACK boilers and their causes. If you are replacing a WILO pump directly in the ATTACK boiler, we also recommend Replacing the WILO Yonos PARA pump in the ATTACK boiler: what you need to know.
Original vs. universal class A pump: is it worth saving?
You can find class A pumps on the market at very different prices – from less than 30 € for unknown Chinese types to 80–150 € for original WILO Yonos PARA or Grundfos ALPHA. Class A guarantees energy efficiency, but not mechanical quality, electronic reliability, or hydraulic curve accuracy. In practice, this means that even a low-quality pump can have an EEI ≤ 0,23 measured under test conditions in the laboratory, but may be unreliable in real operation.
For ATTACK boilers, which are designed and calibrated for specific hydraulic parameters, using an original spare part is a reasonable choice. If your pump breaks down and you want to be sure the new one will fit without the need for additional adjustments, reach for the ATTACK Spare Part - pump RS 25/6-3-PR, 180 mm, which is specifically designed for these boilers and its parameters are tuned to their hydraulics. We elaborate on this topic in the article Original vs universal spare pump for ATTACK boiler: is it worth saving?
Installation of class A pump: what to pay attention to
An EC pump of class A is technologically more sophisticated than the old three-speed models, but its installation is not significantly more complicated. There are a few specifics to keep in mind:
- Shaft orientation – most modern EC pumps can operate in any position, but the electronic head must point upward or sideways – never downward. Overheating of the electronics in an unsuitable position is a real risk.
- Electrical connection – EC pumps require standard 230 V / 50 Hz power supply, but the inverter electronics are sensitive to voltage spikes. It is recommended to install surge protection on the boiler room electrical installation.
- System flushing before installation – never install a new class A pump into an old system with dirt without prior flushing. A magnetic filter (e.g. Fernox TF1 or Spirovent) before the pump significantly extends its lifespan.
- Thread sealing – use Teflon tape or a reverse (hemp + paste) sealing kit. Chemical sealants like Loctite are suitable only for stationary joints, not for pumps, where disassembly may be necessary.
- First start-up and air venting – after installation, it is necessary to vent the system, set the operating pressure (standard 1.5 bar in cold state), and check the tightness of the joints.
A more detailed procedure including common mistakes can be found in the article Installation of a circulation pump into an ATTACK boiler: procedure and common mistakes.
Operating costs and return on investment calculation
Many customers are interested in a concrete answer: how many years will it take for my investment in a new class A pump to pay off? The calculation is relatively simple, but depends on several variables. We present an example for a typical family house:
| Parameter | Old pump (class D) | New pump (class A) |
|---|---|---|
| Average power consumption | 75 W | 10 W |
| Operation / year | 6 000 hours | 6 000 hours |
| Annual electricity consumption | 450 kWh | 60 kWh |
| Annual costs (0,22 €/kWh) | 99 € | 13,20 € |
| Annual savings | 85,80 € | |
| Price of new class A pump | 80 – 130 € | |
| Return on investment | 1,0 – 1,5 years | |
The table clearly shows that the return on investment for a class A pump is on average 12 to 18 months. With a projected lifespan of 15 years, this means a net savings of about 1 200 € during the entire lifetime of the device – and that at current electricity prices. If energy prices continue to rise, the savings will be even higher.
Common questions (FAQ)
Can I install any class A pump into an ATTACK boiler, or must I use an original one?
Technically, you can install any class A pump with the correct hydraulic parameters (25/6) and the correct construction length (130 or 180 mm). Original ATTACK/WILO spare parts are, however, specifically tuned to the hydraulics of particular boilers, which means that after installation, you will not have to deal with system hydraulic tuning. In addition, original spare parts do not void the boiler warranty. In the case of using a non-original pump, there is a risk of a dispute over liability for damage in the event of a failure.
Is a class A pump quieter than an old one? Or does it depend on the type of installation?
EC pumps of class A are generally quieter than old asynchronous types, as smooth speed control avoids resonant frequencies. However, noise can also be caused by the system hydraulics – flow, air bubbles, undersized piping, or unbalanced valves. Replacing the pump with a quieter type does not automatically solve the noise if its cause is elsewhere in the system. If you hear noise or cracking after replacement, check the venting and flow conditions.
Why does a class A pump sometimes consume more than expected?
If you measure the consumption of a class A pump and see a higher power consumption than 20–30 W, it is likely set to an inappropriate mode or to a too high pressure point. Check the settings: if the pump is in CP (constant pressure) mode set to maximum, it will run continuously at higher speeds. The correct setting for most family homes is PP (proportional pressure) at a medium value. Another cause may be undersized piping, where the pump is struggling with high resistance.
Can I use a class A pump in old gravity systems?
Yes, but with caution. Old gravity systems have open expansion tanks and different pressure parameters. An EC pump in such a system can function, but its automatic pressure regulation will work differently than in a closed system. Before installation, it is necessary to verify whether the system is suitable for conversion to a closed loop with a pressure expansion device – this is a prerequisite for the correct function of a class A pump. In case of doubts, consult a specialist.
How long will a class A pump last and what harms it the most?
Manufacturers guarantee a projected lifespan of 15–20 years. In practice, the lifespan depends mainly on the quality of the water in the system and the presence of a magnetic filter. The most common cause of premature failure of EC pumps is bearing corrosion due to impurities and oxides in the circulating water. A magnetic filter installed before the pump and regular inspection/emptying of the filter once a year can realistically extend the pump's lifespan by years. The second enemy is a voltage spike in the electrical grid – surge protection in the boiler room distribution board is recommended.
Is there any marking or label visible on a class A pump?
Yes. Every class A pump must have a label with the EEI (Energy Efficiency Index) value according to EU regulation, which must be ≤ 0,23. In addition, the label shows the rated power (W), hydraulic power, weight, maximum medium temperature, and operating pressure. On the pump itself, there is usually a small energy label similar to those on appliances (fridges, washing machines), where the class A is indicated. If such a label is missing on the pump or the EEI is not listed in the technical documentation, we recommend not to buy the product – it may be a product that does not meet EU regulations.
Conclusion: Class A is not just a marketing term
The energy efficiency class A of circulation pumps is a legal and technical requirement with a real impact on your annual costs. An EC motor with continuous speed control, low EEI, and intelligent automation are not just advertising claims – they are measurable properties worth monitoring and comparing. When selecting a pump for the ATTACK boiler, pay attention not only to the fact that the pump is class A, but also to the correct construction length, suitable hydraulic parameters, and, if possible, warranty support from the manufacturer or seller.
An investment in a quality class A pump pays for itself in practice within two seasons and brings clean savings for the rest of the device's lifetime. If you are choosing between an original spare part and a cheaper alternative, consider the total cost of ownership – not only the price at the checkout, but also the likelihood of system failure in the middle of the heating season. In the case of ATTACK boilers, where the pump is an integral part of the hydraulics, it pays off to choose a proven solution.
Do you have a question on this topic?
Are you unsure or dealing with a specific situation in your household? Write to us – we are happy to help.