What do the numbers in the Avansa pump name mean – power, head, and spacing
What do the numbers in the name of the Avansa pump mean – performance, head and spacing
When a customer opens a catalog of circulation pumps for the first time and sees names like AVANSA 15-6/130 or AVANSA 25-4/180, most of them stop and ask: what do these numbers actually mean? Are they choosing the right one, or will they end up with a pump that is either insufficient or overdimensioned? From practice, I know that misreading the type designation is one of the most common causes of problems when replacing or installing a pump for the first time. This article will therefore explain in detail what each part of the name tells you about the pump, what real consequences the choice of the wrong parameter has, and how to easily navigate the designations.
Structure of the Avansa type designation – three blocks of information
The type designation of the Avansa circulation pump consists of three main blocks separated by a space, a dash and a slash. Each block carries a specific technical information. At first glance, it looks like a random combination of numbers, but in reality it is a standardized system used by practically all European manufacturers of circulation pumps – including Grundfos, Wilo, DAB or Caleffi. Once you understand this system, you will be able to read the parameters of any circulation pump without having to look at the technical data sheet.
The format looks like this: [brand] [DN] – [H] / [L], where:
- DN – nominal diameter (pipe diameter / hydraulic power in millimeters)
- H – maximum head in meters of water column
- L – axial distance of connections (spacing) in millimeters
Let's look at a concrete example: AVANSA 15-6/130 – the number 15 indicates the nominal diameter (DN15, which corresponds to a 1" thread), the number 6 indicates the maximum head of 6 meters of water column, and the number 130 is the connection spacing of 130 mm. That's simple enough. In the following sections, we will examine each block in detail and show why each one matters.
First number – DN and what it says about the hydraulic power of the pump
The first number in the designation (15 or 25 for Avansa pumps) is the so-called nominal diameter DN (from the Latin Diameter Nominalis). In practice, this means the internal diameter of the pump's connection in millimeters. The larger the DN, the greater the volume of water the pump can transport at the same pressure. For typical home heating systems, we most often encounter DN15 and DN25 values.
DN15 corresponds to a connection thread of G1" (1 inch) and is intended for smaller systems – typically radiator heating in an apartment or a smaller house with a boiler output of up to 15–20 kW. The flow that the DN15 pump can provide is usually up to 1.5–2 m³/h. This is enough to heat an apartment with an area of up to 80–100 m² with standard insulation.
DN25 corresponds to a connection thread of G6/4" (one and a quarter inch) and refers to a category of pumps for larger family homes, systems with a larger number of circuits, floor heating or combined systems. The flow can reach 3–6 m³/h depending on the specific model and setting. Typical use is with a boiler with an output of 20–50 kW and a heated area of 100–250 m².
Important: DN is not the same as the external thread diameter! The relationship is as follows – DN15 = G1" (external thread diameter ≈ 33.25 mm), DN25 = G6/4" (external thread diameter ≈ 47.80 mm). If you are not sure which thread you need for your system, read the separate article What connection thread do I need – 1" or 6/4" for the Avansa pump in this Knowledge Center – there you will also find a guide for measuring an old pump.
Why to avoid confusing DN15 and DN25
From practice, I know cases where an installer replaced an old DN25 pump with a new DN15 one just because it was cheaper, and thought that adapters would solve the problem. The result? The system had insufficient flow, the boiler cycled, and radiators in more distant rooms did not heat up. On the other hand, if you install a DN25 pump in a small system, it may not cause a breakdown, but the system will operate at a suboptimal point of the characteristic and the pump will be unnecessarily noisy.
Second number – head and what it really means
The second number in the designation (4 or 6 for Avansa pumps) indicates the maximum head in meters of water column (shortened to mH₂O or simply "H"). This is probably the most important parameter for the correct dimensioning of the pump, and at the same time the one that customers most often misunderstand.
Head is not the height of the building! It is an expression of the hydraulic resistance that the pump must overcome to maintain the required water flow in the system. Hydraulic resistance is created by the friction of water against the walls of the pipes, through valves, fittings, heat exchangers and control elements. The longer and narrower the pipes, the more bends and fittings, the greater the resistance and the higher the head must be.
Physically: 1 m of water column = 0.1 bar = 10 000 Pa (Pascal). When we therefore talk about a pump with "6 m", we are talking about a maximum pressure of 0.6 bar that the pump is capable of creating at zero flow. In real operation – that is, at some flow – this pressure is lower. The relationship between flow and head is described by the pump characteristic curve (QH curve).
How to calculate what head is sufficient for you
For standard domestic heating systems, a simple orientation method applies. Hydraulic resistance depends on the length of the longest circuit (in meters) and on the specific pressure loss in the piping. For dimensioning, the value of 100–150 Pa/m is commonly used for standard heating, which corresponds to 0.01–0.015 m of water column per meter of pipe.
Practical example: a family house with a circulation system, where the longest circuit is 40 meters (there and back = 80 m of piping) with a specific loss of 100 Pa/m:
- Total loss in the piping: 80 × 100 Pa = 8 000 Pa = 0.8 m H₂O
- Losses in fittings, valves and heat exchanger: approx. 50–100 % of piping losses = another 0.4–0.8 m
- Total resistance: approx. 1.2–1.6 m H₂O
In this case, a pump with a head of 2 m would theoretically be sufficient. Why then do we sell pumps with H=4 m or H=6 m? Because:
- Calculations are approximate and reality differs (clogged pipes, additional fittings, control valves...)
- The pump never operates at the maximum head point – it works in the middle part of the curve
- Systems are expanded, renovated, and new circuits are added
- For floor heating, losses are significantly higher (long tubes with small diameter)
For most family houses with radiator heating and a boiler up to 30 kW, AVANSA 25-4/130 or AVANSA 25-4/180 are the right choices. For houses with floor heating or significantly longer circuits, go for AVANSA 25-6/130.
Why over-dimensioned head is a problem
You might think that a higher head = a better pump = a safer choice. Wrong! A pump with too high a head in a system with low resistance will operate at an unsuitable point on the curve – it will pump too high a flow. This has several consequences:
- Noise in the piping (whistling, humming, cavitation in fittings)
- Increased electricity consumption
- Faster wear of thermostatic valves
- Worse control comfort – rooms are harder to adjust to the desired temperature
The opposite extreme – too low a head – will cause insufficient flow, distant radiators will be cold and the system will not be able to deliver the heat from the boiler.
The third number – pitch and why it is crucial for installation
The third number (130 or 180) expresses the axial distance between the pump connections in millimeters. In practice: it is the distance between the centers of the inlet and outlet nozzles of the pump. This number directly indicates the gap that must be available on the piping for pump installation. If you have prepared connections with a pitch of 130 mm in the system and you buy a 180 mm pump, it simply won't fit without pipe reconstruction.
Standardized pitches for circulation pumps in Europe are: 130 mm and 180 mm. Sometimes you may also encounter values of 110 mm (for smaller systems) or 200 mm (for industrial applications), but for domestic heating systems, 130 mm and 180 mm are the absolute norm.
How to measure the pitch of an existing pump
If you are replacing an old pump, you can easily measure the pitch: using a calibrated sliding caliper or a regular centimeter ruler, measure the distance between the centers of both connecting nozzles (not between the edges, but between the axes). If you are unsure where the axis is, you can measure from the center of one sealing face to the center of the other.
If you get a number around 125–135 mm, go for a model with a 130 mm pitch. If you get 175–185 mm, go for a model with an 180 mm pitch. A larger deviation than ±10 mm from the standard indicates either an older non-standard type or a measurement error.
What to do if the pitch doesn't match
Sometimes it happens that the required pitch is 180 mm, but you only have a 130 mm model in the store (or vice versa). There are two solutions: buy the correct model, or use extension adapters and transitions. Adapters do exist, but each additional sealed joint is a potential leak point. In practice, I recommend buying a pump with the correct pitch – you'll save time, materials, and nerves.
Special case: marking AUTO and the letter E
In the Avansa range, in addition to standard pumps, you will also find AVANSA AUTO 25-4/180 E. What do the additional words and the letter mean?
AUTO in the name means that the pump is equipped with automatic regulation. Instead of a fixed power setting, the pump adapts to the actual needs of the system – it automatically evaluates hydraulic conditions and adjusts the speed so that the system operates optimally. This has a significant impact on electricity consumption (savings of 30–60 % compared to a classic pump with fixed speeds) and comfort (quieter operation, better temperature control).
E at the end of the designation is an abbreviation for "Electronically controlled" (electronically controlled). This information complements the data on the type of drive and control. Classic pumps have an asynchronous motor with 2–3 fixed power levels. Electronic pumps with the marking E have a synchronous or EC motor (electronically commutated), which is significantly more efficient across the entire speed range.
The basic numerical structure remains the same: 25-4/180 = DN25, max. 4 m, pitch 180 mm. The letters and prefixes only specify the type of regulation and drive. If this topic interests you more, I recommend reading the article Electronic vs. standard Avansa circulation pump – is it worth paying extra for the AUTO version, where these differences are analyzed in detail including economic return.
Comparison of Avansa models – parameters side by side
For a better overview, I list all available models in a simple table:
| Model | DN | Thread | Max. H [m] | Pitch [mm] | Typical use |
|---|---|---|---|---|---|
| AVANSA 15-6/130 | 15 | G1" | 6 | 130 | Apartment, small house, boiler up to 20 kW |
| AVANSA 25-4/130 | 25 | G6/4" | 4 | 130 | Family house, radiators, boiler 20–35 kW |
| AVANSA 25-4/180 | 25 | G6/4" | 4 | 180 | Family house, different installation position |
| AVANSA 25-6/130 | 25 | G6/4" | 6 | 130 | House with floor heating, long circuits |
| AVANSA AUTO 25-4/180 E | 25 | G6/4" | 4 | 180 | Modern house, energy savings, automation |
Practical scenarios from everyday practice – how numbers helped (or didn't help)
Scenario 1: Replacing an old pump in a panel apartment
A customer from Bratislava called to say that his old pump was dripping. It was a fifteen-year-old German pump with the designation "UPS 15-50". The numbers 15 and 50 in the old Grundfos system indicate a DN15 diameter and a maximum pumping head of 5 meters (in older notation, it was sometimes stated in dm, i.e., 50 dm = 5 m). The center distance was 130 mm. The correct replacement was therefore a model with DN15, H at least 5–6 m, and a center distance of 130 mm. AVANSA 15-6/130 was a perfect fit – the same center distance, 1" thread, and pumping head of 6 m (slightly higher than the original, which is acceptable). The replacement took 20 minutes.
Scenario 2: A new boiler room in a family house with underfloor heating
An installer was working on project documentation for a two-story house of 180 m² with underfloor heating on both floors. The total length of the pipes was over 600 m (3 loops of approx. 200 m). The hydraulic resistance calculated to 4.8–5.2 m water column. The correct choice was the model AVANSA 25-6/130, because a pumping head of 4 m would have been on the edge and would not have been sufficient in case of system clogging (after years of operation). The center distance of 130 mm matched the prepared installation in the boiler room. Since the customer was also concerned with energy efficiency, we discussed the version AUTO 25-4/180 E, but the hydraulics required a higher head, so we stayed with the 25-6 model.
Scenario 3: A customer bought the wrong center distance online
This is unfortunately a classic case. A customer bought a pump 25-4/130 without measuring the existing installation. When the installer arrived, they found out that the original pump in the boiler had a center distance of 180 mm. The 130 mm pump simply could not be mounted in the prepared threads without extending the piping. The solution was to replace it with the correct model – AVANSA 25-4/180. Unnecessary travel, waiting, and complications that could have been avoided by measuring before ordering.
Performance stages – what they have in common with the numbers in the name
Standard Avansa pumps (not the AUTO version) have 3 performance stages. These stages allow you to set the pump to a suitable operating point without having to change the entire pump. The digits in the name indicate the parameters at maximum – third – stage. This is important to know when dimensioning: if the calculation shows that the required pumping head is 3.5 m, a pump with H=4 m (third stage) gives you a reserve and you can actually operate it in the second stage, where it will be quieter and more energy-efficient.
Dependence of the numbers in the name on the type of heating system
Not every system has the same requirements. Here is an approximate overview of how the numerical parameters change according to the type of installation:
- Radiator system in an apartment (50–80 m²): DN15, H=4–6 m, center distance 130 mm → AVANSA 15-6/130
- Radiator system in a house (100–200 m²): DN25, H=4 m, center distance 130 or 180 mm → AVANSA 25-4/130 or 25-4/180
- Underfloor heating (100–200 m²): DN25, H=6 m → AVANSA 25-6/130
- Combined system (radiators + UFH): DN25, H=6 m or AUTO version
- Small apartment building: DN25, H=6 m, or possibly a more powerful type
A detailed selection procedure can be found in the article How to choose an Avansa circulation pump for your heating system, where additional criteria such as medium temperature, materials, and type of regulation are also discussed.
Where to find the numbers on an existing pump – quick guide
If you are replacing a pump and want to be sure you are buying the right one, look at the label (type plate) on the side of the pump. Every pump must have a production label. On it, you will find:
- Type designation (e.g., "25-4/130") – this is the basis
- Power in watts (W) – for comparison of energy classes
- Power supply (230 V / 50 Hz for standard circulation pumps)
- Maximum medium temperature (usually 110 °C)
- Maximum pressure (usually 10 bar)
- Energy efficiency class (A+, B, C...)
If the label is unreadable (corrosion, fading), measure the center distance and thread physically. In the end, consult the article Setting and regulating the flow of an Avansa pump after installation – there you will also find instructions on how to properly set the performance stage after installation.
Most frequently asked questions (FAQ)
What happens if I buy a pump with a higher pumping head than needed?
The pump will work, but not optimally. It will pump too much flow, which will cause noise (whistling of valves, noise in the pipes), higher electricity consumption, and faster wear of thermostatic valves. For most home systems, H=4 m is sufficient – do not try to buy "with a reserve" for H=6 m where it is not necessary.
Can I replace a 130 mm pump with a 180 mm pump if the larger model is cheaper?
No, without modifying the piping. A 50 mm difference in center distance is not negligible – the pump cannot be physically mounted without rebuilding the connections. Either pay the installer for an extension or buy the correct center distance right away. In the long run, the correct center distance is the cheaper option.
Is the number DN the same as the outer diameter of the thread?
No. DN is the nominal diameter, which corresponds to the inner diameter of the pipe. The outer diameter of the thread is larger. DN15 = G1" (outer diameter ≈ 33.25 mm), DN25 = G6/4" (outer diameter ≈ 47.80 mm). If you measure an old thread with a caliper, you are measuring the outer diameter of the thread, not DN.
Why does AVANSA AUTO 25-4/180 E have "4" in its name if it is more powerful than the standard model?
The number 4 in the name indicates the maximum head (4 m) – that is, the hydraulic parameters of the pump. The AUTO version is not hydraulically more powerful than the standard one, but it is smarter: it automatically adjusts performance according to the system's actual needs. The result is significant energy savings and quieter operation, not higher pressure. The hydraulic parameters remain the same – only the way they are used changes.
How do I determine which setting to use for the pump after installation?
Basic rule: start with the second stage. If distant radiators are cold or the system cannot keep up with heating, switch to the third. If the system is noisy (whistling valves) or rooms are difficult to cool down to a lower temperature, try the first stage. A detailed setup procedure can be found in the article Setting and regulating the pump flow of Avansa after installation.
Can a pump with a larger DN (25) have a lower head than a smaller model (15)?
Yes, and this is common. AVANSA 25-4/130 has a maximum head of 4 m, while AVANSA 15-6/130 has 6 m. Head and DN are independent parameters. A larger DN means a higher possible flow, not necessarily higher pressure. For each application, you need the right combination of both values.
Conclusion: read the names like a mini manual
The model designation of the Avansa circulation pump is not a marketing label – it is a technical manual in short. The three numbers in the name will tell you everything you need to know before purchasing: what the hydraulic performance is (DN), what resistance the pump can overcome (H), and whether it will physically fit into your installation (spacing). When you compare these three parameters with the real needs of your system, selecting the right model is straightforward and quick.
In practice: always measure the spacing of the existing pump before ordering, check the thread diameter, and estimate or have the required head calculated. With these three numbers in hand, go to the overview of Avansa pumps and the selection will take less than five minutes. If you are unsure about any parameter, other articles in this Knowledge Center – for example, How to choose an Avansa circulation pump for your heating system or Common questions about Avansa circulation pumps – will provide further support.
Do you have a question about this topic?
Struggling to decide or dealing with a specific situation in your home? Write to us – we are happy to help.