What do the numbers in the name of the Avansa pump mean – power, head and length

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What the numbers in the Avansa pump name hide – a complete guide to the designation

When you first look at the range of Avansa circulation pumps, you will likely be greeted by a row of names full of digits and slashes: 15-6/130, 25-4/180, 25-6/130… At first glance, it looks like a random combination, but in reality, each number precisely describes one specific technical property of the pump. Anyone who correctly reads these numbers can say within a few seconds whether a given pump is suitable for their system – without having to open a catalog or call the manufacturer.

This article will explain in detail what each digit in the designation means, why it is important from a hydraulic point of view, how these values relate to real conditions in a home heating system, and will show you practical examples where a wrong understanding of the designation led to an incorrectly selected pump – and conversely, where correct reading saved unnecessary costs. If you are looking for an even more detailed selection process, please also see our guide How to choose an Avansa circulation pump for your heating system.

First number: diameter and type of connection – what does the number 15 or 25 mean

The first number in the designation of an Avansa pump indicates the diameter of the pump's flange (neck) in millimeters. It refers to the internal nominal diameter of the hydraulic connection, which directly determines what type of thread (or what pipe size) you need to connect the pump to the piping.

In practice, you will encounter two values with Avansa pumps:

15 – corresponds to an internal diameter of 15 mm, which in standard pipe terminology corresponds to a 1" (one inch) threaded connection. This is a smaller size, typical for compact systems with lower flow rates.
25 – corresponds to an internal diameter of 25 mm, in practice a 6/4" (one and a half inch) thread. This is the standard size for most home boiler rooms with normal heating water flow rates.

It is important to realize that this number does not directly indicate the pump's performance; it refers to the mechanical dimension of the connection. A pump marked 15 cannot be physically connected to a 6/4" thread without a reducer – and vice versa. Therefore, the first number is a key filter when selecting: first look at what piping you have in the boiler room, and choose between the 15 or 25 group accordingly.

Specifically: AVANSA 15-6/130 has a 1" threaded connection and is suitable for installations where the inlet and outlet piping is terminated at 1". In contrast, AVANSA 25-6/130 has the same hydraulic parameters but a 6/4" thread – and is therefore intended for a different type of mounting location, although it is hydraulically just as capable.

If you are interested in details about how threads work and what happens in case of a mix-up, read our article What connection thread do you need – 1" or 6/4" for an Avansa pump, or What thread does a circulation pump need – the difference between 1" and 6/4" connections.

Second number: maximum transport height – the key to pump performance

The second number after the hyphen is the most important hydraulic data in the entire designation. It refers to the maximum transport height of the pump, given in meters (m). Transport height – technically also called manometric height or Hmax – expresses the maximum hydraulic resistance that the pump is capable of overcoming at zero flow. In practice, this means: the higher this value, the greater the pressure (or resistance of the circuit) the pump can handle.

In Avansa designations, you will encounter two values:

4 – maximum transport height of 4 m of water column (≈ 0.4 bar at zero flow)
6 – maximum transport height of 6 m of water column (≈ 0.6 bar at zero flow)

Pumps of the 25-4 series (e.g., AVANSA 25-4/130 or AVANSA 25-4/180) are suitable for less demanding hydraulic circuits – for example, a simple system with a boiler, a few radiators and a short route, where the total pressure resistance of the circuit does not exceed 3–3.5 m. Pumps of the 25-6 series (e.g., AVANSA 25-6/130 or AVANSA 15-6/130) are intended for more complex hydraulic systems, where the route is longer, the pipes have a smaller diameter or there are thermostatic valves in the circuit, which significantly increase the resistance.

How to understand the delivery head in practice

Delivery head is not the same as the physical height of the building. It is the hydraulic resistance of the system converted into meters of water column. In the system, the resistances of all components are added together: pipes, elbows, valves, control valves, distributors, and heating units. The total sum is the pressure loss of the circuit that the pump must compensate for.

Approximate values from practice:

Small family house up to 80 m² with radiators, steel pipes DN15–DN20, solid fuel boiler without thermostats: total pressure loss is usually 1.5–2.5 m → a pump with Hmax 4 m is sufficient
Family house 100–150 m², mixed system (part underfloor heating, part radiators), thermostatic valves on each radiator: total pressure loss 3–5 m → you need Hmax at least 6 m, in some cases even more
Larger building or system with long horizontal runs, plastic pipes of small diameters (PE-X 12 or 16 mm): pressure loss can exceed 5–7 m → consider a higher performance pump or an electronic version with continuous regulation

Important practical note: the pump must never operate continuously at maximum delivery head – this is the zero-flow point, a condition where the pump generates pressure but the water does not flow. In real operation, the pump's operating point must be within its characteristic curve, not at its edge. If the required delivery head in the calculation comes out just below the pump's maximum (e.g., you need 3.8 m and the pump has a max of 4 m), it is usually safer to choose a more powerful model.

The number after the slash: construction length (flange spacing) in millimeters

The third parameter in the designation – the number after the slash – is sometimes overlooked when selecting a pump online, but in the boiler room it is the first thing you must measure before any order. It refers to the construction length of the pump, also known as the flange spacing or center-to-center distance of the nozzles. It is given in millimeters and indicates the distance between the centers of the pump’s inlet and outlet nozzles.

In the Avansa range, we encounter two variants:

/130 – flange spacing 130 mm. This is a shorter model, historically very common in domestic boiler rooms. Most older installations from the 70s to 90s were designed for this length.
/180 – flange spacing 180 mm. A longer model, common in more modern and foreign boiler rooms, as well as in some older industrial applications.

Why is the construction length so important?

The pump in the boiler room is installed into a pre-made pipe section. The inlet and outlet nozzles of the boiler, storage tank, collector, or piping are fixed – their mutual distance is fixed once and for all. If you buy a pump with a different dimension, you will not be able to physically connect it without extending or shortening the pipe run, which is unnecessary work and usually an unnecessary cost in an existing installation.

From practice: a very common situation when replacing an old pump (e.g., after 15 years of operation) is that the customer comes with the request "I want the same, just new". The first thing we must find out is the flange spacing – because if the original pump has 130 mm, a new one with 180 mm will not fit without modifications, and vice versa. That is why you should always measure the construction length of the existing pump or the distance between the threaded nozzles in the piping before placing an order.

For example, AVANSA 25-4/130 and AVANSA 25-4/180 are hydraulically identical pumps – same flow rate, same delivery head, same 6/4" thread – the only difference is the length. Which one you choose depends entirely on how much space you have in the piping.

For more detailed information on measurement and installation, read the article Step-by-step installation of the Avansa circulation pump. The issue of construction length is also discussed in detail in the article What do the numbers in the name of the Avansa pump mean – performance, delivery head, and flange spacing.

Combination of parameters: how to read the full name at once

Now that we know each number individually, let's look at how they work together. Take the example of the designation AVANSA 25-4/180:

25 → connection thread 6/4" (nozzle inner diameter ~25 mm)
4 → maximum transport head 4 m water column
180 → construction length (connection spacing) 180 mm

Thus, without opening any catalog, you know: this pump has a 6/4" thread, can handle circuits with hydraulic resistance up to about 3.5 m, and you need to have exactly 180 mm of free space in the pipe between the inlet and outlet. These are three conditions that must be met simultaneously.

Similarly for AVANSA 15-6/130:

15 → thread 1"
6 → maximum transport head 6 m (hydraulically more powerful than the -4 series)
130 → construction length 130 mm

This pump is physically smaller (1" thread), but hydraulically more powerful than, for example, 25-4/130 – it can overcome a higher circuit resistance. It is suitable, for example, for installations with 1" piping, where the circuit is longer or contains thermostatic valves.

Electronic version AUTO E – what changes in the designation

A special category is AVANSA AUTO 25-4/180 E. The number system remains the same (25 = thread 6/4", 4 = Hmax 4 m, 180 = spacing 180 mm), but two additional designations are added in the name: AUTO and E.

E – electronically controlled pump with an EC motor (electronically commutated motor). Unlike a standard three-speed pump, the electronic version can smoothly adjust the speed according to the system's current needs. Result: significantly lower electricity consumption (typically 5–15 W vs. 50–90 W for a standard pump).
AUTO – the pump operates in automatic mode, where it automatically monitors the pressure in the circuit and flow, and adjusts the performance accordingly. You do not need to manually switch speeds.

The hydraulic parameters remain: maximum transport head 4 m, thread 6/4", spacing 180 mm. From the installation point of view, the AUTO E is mounted in the same place as the standard 25-4/180 – the replacement is a 1:1 swap. What changes is the operational benefit and energy consumption. A detailed comparison can be found in the articles Electronic vs. standard Avansa circulation pump – is it worth paying extra for the AUTO version and Avansa standard vs. electronic (AUTO E) – which circulation pump is more worth it.

Pump flow and its relation to the designation

A careful reader may have noticed that the numerical designation itself does not include the value of maximum flow (Qmax). This is not an error or an oversight – flow is a function of the transport head and depends on the Q-H characteristic of the pump. The higher the circuit resistance, the lower the flow; at zero resistance, the flow is maximum.

Approximate values of maximum flow for Avansa pumps according to the designation:

Series -4 (Hmax 4 m): maximum flow at zero resistance typically around 2.5–3.5 m³/h
Series -6 (Hmax 6 m): maximum flow typically around 3–4 m³/h

In the normal operation of a typical family house, the pump's operating point lies somewhere in the middle of the H-Q curve – that is, not at maximum flow or maximum head. A typical operating point for a house of 120–150 m² is a flow of 1–2 m³/h at a transport head of 1.5–3 m.

If you want to know how to precisely calculate the required flow and transport head for your specific house, we recommend the articles How to choose an Avansa circulation pump for your heating system and Setting and regulating the flow of an Avansa pump after installation.

Overview table of Avansa models and their parameters

Model	Thread	Hmax (m)	Spacing (mm)	Motor type
AVANSA 15-6/130	1"	6	130	standard
AVANSA 25-4/130	6/4"	4	130	standard
AVANSA 25-4/180	6/4"	4	180	standard
AVANSA 25-6/130	6/4"	6	130	standard
AVANSA AUTO 25-4/180 E	6/4"	4	180	electronic (EC)

Typical mistakes when selecting based on the designation – examples from practice

Over the years of practice in selling heating technology, we repeatedly encounter several typical mistakes that arise precisely from misreading the designation. Here are the most common ones:

Mistake No. 1: Purchasing a pump with the wrong construction length

A customer orders a new pump because the old one has stopped working. They do not measure the spacing and order a 25-4/130, while they have a 25-4/180 in the boiler room. The pump arrives, and the customer realizes that the nozzles do not fit by 50 mm. The piping must be shortened, and the flanges must be welded, which in an existing copper or steel installation means hours of additional work for the plumber. Prevention: one measurement with a tape measure before ordering will save hours of work.

Mistake No. 2: Choosing a weak pump for a circuit with thermostatic valves

The house has thermostatic valves installed on all radiators. The customer sees that "a -4 pump is enough for 130 m²" and orders a cheaper version. The problem arises during the transitional period when most thermostats close – the circuit resistance rises sharply, and the pump with Hmax 4 m cannot overcome the residual pressure. Result: the pump runs at maximum, is noisy, and some radiators are cold. Solution: for systems with thermostatic valves, always choose a -6 or an electronic AUTO E version, which adapts to the resistance.

Error #3: Bigger thread = higher performance pump

Some customers assume that a larger thread means a more powerful pump. That is why they choose 25-4 instead of 15-6, because "25 is obviously bigger." In reality, 15-6 has a Hmax of 6 m, while 25-4 has Hmax of only 4 m. From a hydraulic performance standpoint, a pump with a smaller thread can be more powerful than a pump with a larger thread. The thread only determines the physical connection, not the performance.

Error #4: Ignoring the construction length when purchasing a "replacement" pump of a different brand

The customer wants to replace an old pump (e.g., Grundfos) with an Avansa. The parameters match, but they forget to check the construction dimensions. The result is the same as in error #1 – physically incompatible dimensions. Rule of thumb: before replacing with a different brand, always compare the technical specifications of both pumps.

Practical approach: how to choose the right Avansa model in three steps

Based on everything we have discussed, the selection process is quite simple:

Measure the flange spacing of the existing pump or the free pipe section. You will get a value of 130 or 180 mm – this determines the third number in the designation.
Check the thread on the inlet and outlet pipe nozzles – is it 1" or 6/4"? This determines the first number (15 or 25).
Estimate the hydraulic resistance of the system: a simple loop without thermostats → -4 is sufficient. Longer routes, small-diameter plastic pipes, thermostatic valves → choose -6 or consider AUTO E.

After these three steps, you will know exactly which model from the Avansa range you are looking for – without unnecessary calls or guessing.

Frequently asked questions (FAQ)

Can I use a 25-4/130 pump instead of a 25-6/130 if it is cheaper?

It depends on your system. If your loop is not hydraulically demanding (short piping, no thermostatic valves, the boiler is close to the radiators), then a pump with Hmax of 4 m will likely be sufficient. However, if you have longer routes, multiple floors, thermostatic heads, or underfloor heating with small-diameter pipes, you risk insufficient circulation in parts of the system. In case of doubt, we recommend -6 – it is not a significantly more expensive model and the safety margin is worth it.

What happens if I install a pump with the wrong construction length?

Physically, you will not be able to connect it to the system without modifying the piping. With a shorter pump (e.g., 130 mm instead of 180 mm), a gap will appear between the pump nozzles and the piping, which must be bridged with an extension nipple. With a longer pump (180 mm instead of 130 mm), there will be no space, and the piping must be extended or modified. Therefore, measuring the distance is the first obligation before any order.

Why does AVANSA 15-6/130 have a 1" thread even though the number 15 is smaller than 25?

The numbers 15 and 25 represent the nominal internal diameter of the nozzle in millimeters. A 1" (inch) thread has an outer diameter of approximately 33.3 mm and an inner diameter of approximately 26.4 mm, which is close to 25 mm – not 15 mm. In reality, this is a conventional nomenclature, where the number "15" in the pump designation does not refer to the exact millimeter dimension of the thread, but to the series category. A 1" thread physically corresponds to the pipe diameter DN15 (nominal diameter of 15 mm pipe), while the thread itself has a larger dimension. Therefore: AVANSA 15 = 1" thread, AVANSA 25 = 6/4" thread.

What is the difference between AVANSA 25-4/130 and AVANSA 25-4/180 apart from the length?

Hydraulically, they are identical. Same head, same maximum pumping height, same maximum flow, same motor power, same energy efficiency class. The only difference is the construction length – 130 or 180 mm. The choice depends exclusively on the dimensions of your installation.

Is AVANSA AUTO 25-4/180 E sufficient for a larger house, even though it only has Hmax of 4 m?

The electronic regulation of AUTO E significantly improves operational efficiency, but it does not change the maximum pumping height. If your system requires Hmax more than 4 m (which is typical for houses larger than 180 m² with strong hydraulic resistance), the pump AUTO 25-4/180 E will not be sufficient – regardless of the electronics. In such a case, you need a more powerful hydraulic model.

Can I connect a 1" pump to a 6/4" system using a reducer?

Technically yes, a reducer from 1" to 6/4" exists and is not expensive. However, when choosing a new pump, this solution is not recommended – every reducer is an additional weld or threaded connection, and thus a potential leak point. In addition, a reducer to 1" can be a hydraulic bottleneck if the flow is higher. The correct choice is always a pump with the same thread as your system.

Conclusion: three numbers that will save you time and money

The Avansa pump labeling system is not complicated – on the contrary, it is a logically organized code, where each number precisely describes one physical or hydraulic property. The first number indicates the type of thread and the nozzle diameter (15 = 1" thread, 25 = 6/4" thread). The second number indicates the maximum pumping height in meters, i.e., the hydraulic performance of the pump (4 m or 6 m). The number after the slash is the construction length – the distance between the connections in millimeters (130 or 180 mm), which determines the physical compatibility with your piping.

If you can correctly read and compare these three values with the conditions of your installation, selecting the right pump becomes a matter of minutes, not hours. You will avoid situations where the pump physically does not fit into the piping, or where after installation you discover that the system does not heat distant radiators.

The full range of Avansa circulation pumps is available on the Avansa category page. If you are unsure about the selection for your specific system, check out other articles in this Knowledge Center – for example, Avansa vs. other circulation pumps – what to look for when choosing a brand or Avansa AUTO E vs. standard – which circulation pump is more cost-effective.

Do you have a question about this topic?

Not sure how to decide or dealing with a specific situation in your home? Write to us – we are happy to help.