How to choose an Avansa circulation pump for your heating system
How to choose an Avansa circulation pump for your heating system
The circulation pump is the heart of every central heating system. When it works properly, you won't even notice it – water circulates, radiators warm up and you enjoy the heat. However, if you choose the wrong pump, problems start to accumulate: noisy pipes, cold radiators at the end of the branch, an overloaded boiler or unnecessarily high electricity bill. In this guide, we will look at how to choose the right Avansa circulation pump for your specific system – step by step, with real-life examples from practice.
If you're here for the first time and don't know what the numbers in the name such as 25-4 or 25-6 mean, I recommend reading the article What do the numbers in the name of the Avansa pump mean – power, head and pitch in our Knowledge Center first. This article, on the other hand, assumes that you are familiar with the basic terminology and focuses on the practical selection according to the specific parameters of your system.
Why pump selection is more important than it seems
In practice, I meet two types of customers. The first type buys a pump based on price – they take the cheapest one that looks similar to the old one. The second type wants the "most powerful" one, because they think more power can never hurt. Both approaches are wrong and both lead to problems.
An underdimensioned pump cannot push enough water through the system, resulting in cold radiators in distant parts of the house and a boiler that keeps firing because the return is too cold. An overdimensioned pump, on the other hand, causes hydraulic noise – gurgling and knocking in the pipes – and unnecessarily increases electricity consumption. In extreme cases, it can even cause erosive cavitation in the pipes and fittings.
A properly dimensioned Avansa pump is one that covers the hydraulic resistance of your network with a slight reserve and at the same time operates in the optimal point of its characteristic. How to do it? Let's proceed systematically.
Step 1: Determine the thermal power of your system
The first thing you need to know is the thermal power of your boiler or heat source. This data can be found on the boiler's nameplate, in the technical documentation or in the project report. It is given in kilowatts (kW).
From the thermal power, you can derive the required water flow through the system. The basic formula is:
Q = P / (c × ΔT)
where Q is the flow in liters per second, P is the power in kW, c is the specific heat capacity of water (4 187 J/kg·K, rounded to 1.16 Wh/l·K) and ΔT is the temperature difference between the supply and return in Kelvins (°C).
In practice, we work with a standard temperature difference of 10 to 20 °C. For an older system with cast iron radiators and temperatures of 75/55 °C, we consider ΔT = 20 °C. For more modern condensing boiler systems with temperatures of 55/45 °C, we consider ΔT = 10 °C. Low-temperature floor heating works with a ΔT of only 5–8 °C and requires a significantly higher flow.
Practical example: You have a condensing boiler of 20 kW, the system operates at 55/45 °C (ΔT = 10 °C). Required flow:
Q = 20 000 W / (1.16 × 10) = 20 000 / 11.6 ≈ 1 724 W/h → converted to l/h: 20 kW × 860 / 10 °C = 1 720 l/h
This is the amount of water that the pump must push per hour. Remember this number, you will need it when selecting a specific model.
Step 2: Calculate the required head
The head (given in meters of water column, mH₂O) expresses the hydraulic resistance that the pump must overcome. This resistance depends on the length of the pipe, the diameter of the pipes, the number of elbows, valves, filters and radiator valves.
An exact calculation is a matter of the project. In practice, however, there is a quick orientation method: calculate with a resistance of 1.5 to 2.0 Pa per meter of the longest branch (for standard pipes DN 15–20 mm at typical speeds of 0.3–0.7 m/s). For a simple family house with the longest branch of 15 m, this comes to a resistance of about 30–45 Pa, which is 0.3–0.45 mH₂O. With local resistance of fittings, valves and boiler heat exchangers (typically 1–2 m), you get a resulting required head of 2–4 m for most standard family houses.
More complex houses with long branches, floor heating or many zones may require a head of 4–6 m. Large objects, apartment buildings or industrial halls obviously require even more.
Step 3: Choose the type of pump – manual or electronic
Avansa offers two basic categories of pumps: classic three-speed (manual setting) and electronic with automatic regulation. Each has its place.
Classic three-speed Avansa pumps
These pumps offer three fixed speeds (stage I, II, III). You set them manually according to the system's needs, and the pump operates at a constant performance. They are simple to operate, reliable, and fully sufficient for most family homes when set correctly.
Examples from the Avansa range:
- AVANSA 15-6/130 – compact pump with 1" thread, suitable for smaller systems up to approx. 15 kW
- AVANSA 25-4/130 – 130 mm spacing, 6/4" thread, covers typical family homes
- AVANSA 25-4/180 – same hydraulics, but longer motor (180 mm spacing) for installations with greater distances between connections
- AVANSA 25-6/130 – higher head of 6 m, for systems with higher resistance or longer branches
Electronic Avansa AUTO pumps
The model AVANSA AUTO 25-4/180 E is an electronically controlled pump with an EC motor and automatic adaptation to the current system condition. It regulates performance smoothly according to differential pressure or flow, not in three steps. The result is lower energy consumption (class A – up to 80% saving compared to older pumps), quieter operation, and longer lifespan.
For whom is the electronic version worth it and for whom is the classic version sufficient? I cover this in detail in a separate article Electronic vs. standard Avansa circulation pump – is it worth paying extra for the AUTO version, but briefly: if you plan to use thermostatic heads on radiators, zone controls, or a modulating boiler, the electronic version significantly increases comfort and reduces costs. For a simple system without thermostats and with a single fixed zone, a classic pump is sufficient.
Step 4: Compare the Avansa model parameters with your requirements
Now you have two key numbers: required flow (e.g. 1 720 l/h = 1.72 m³/h) and required head (e.g. 3.5 m). These values must be compared with the Q-H characteristic of each model.
On the graph you can see the typical shape of Q-H curves for individual models. Your operating point (the intersection of the required flow and head) must lie below the pump curve at the selected stage, ideally in the middle third of the curve, not at the edges (where the pump is inefficient).
Specific recommendations for typical situations:
- Small family home, boiler 10–15 kW, simple system: AVANSA 15-6/130 with 1" thread is an ideal solution. Compact, inexpensive, low-maintenance.
- Standard family home 150–250 m², boiler 15–25 kW, network resistance up to 4 m: AVANSA 25-4/130 or AVANSA 25-4/180 depending on spacing.
- Larger home or long branches, network resistance 4–6 m: AVANSA 25-6/130.
- Home with thermostatic heads and zoning: AVANSA AUTO 25-4/180 E.
Step 5: Check the dimensions – spacing and connection thread
Hydraulic parameters are one thing, physical dimensions are another – and customers often forget about them surprisingly often. The new pump must physically fit in place of the old one, otherwise the plumber will face unnecessary work modifying the piping.
Two key measurements:
- Spacing (center-to-center distance of connection nozzles): Avansa offers pumps with 130 mm spacing (compact, suitable for most standard installations) and 180 mm spacing (for older installations or specific mounting conditions).
- Connection thread: 1" (inch) for smaller pumps, 6/4" (six-quarter) for larger models. Most boilers and modern installations in Europe use a 6/4" connection.
How to determine the dimensions of the old pump? Measure the distance between the centers of the connection nozzles with a caliper and identify the thread size. If you have any doubts, pay attention to the article What connection thread do you need – 1" or 6/4" for the Avansa pump in our Knowledge Center, where you will also find a visual guide to identifying the thread.
Important note from practice: when replacing an old pump with Avansa, it often happens that the old pump had a center distance of 130 mm, but the piping is bent or welded in such a way that the new pump simply does not fit without modification. In such a case, the solution is a model with an 180 mm center distance and appropriate reduction, or a short coupling. Always verify this before ordering.
Step 6: Consider the motor orientation and placement in the system
Avansa circulation pumps are designed for horizontal shaft installation, which is standard for most heating systems. The motor (electronics) must always be placed on the side or on top – it must never point downward, as this would result in insufficient lubrication of the bearings and reduced lifespan.
Always install the pump on the return pipe (return line), where the water temperature is lower. The reason is practical: lower temperature reduces the risk of cavitation and extends the life of seals and bearings. In addition, the pump on the return pipe has access to the static pressure of the entire system, which improves its hydraulic conditions.
Always install ball valves on both sides near the pump – they allow the pump to be replaced without draining the entire system. If the system does not have a filter (sludge trap), I strongly recommend adding one before the pump inlet. Dirt, soot, scale, and remnants from installation are the most common causes of premature damage to circulation pumps – this applies to any brand, not just Avansa.
Most common mistakes when choosing a circulation pump
Over the years of working with customers, I have seen recurring mistakes. Here are the most common ones:
Mistake 1: Choosing based on the size of the old pump
“Give me the same as I had” – one of the most common statements. The problem is that the old pump may have been oversized during installation, or the system has undergone changes since then. Always verify with a calculation, not just physical dimensions.
Mistake 2: Ignoring the difference between 130 mm and 180 mm center distance
The customer orders an AVANSA 25-4/130, but the boiler room has an old installation with an 180 mm center distance. The result: the pump does not fit, the plumber has to improvise, and unnecessary costs arise. Always measure the center distance.
Mistake 3: Choosing based on maximum performance
“If I am not sure, take a stronger one.” A powerful pump operating at low flow rates near the zero point of the curve – that is, at high pressure and low flow – results in noise, vibrations, energy waste, and faster bearing wear.
Mistake 4: Forgetting the filter
New pump, no filter. After a season, the rotor is blocked by sediment. The cost of replacement is many times higher than the price of the filter. A sludge trap is mandatory equipment for every installation.
Mistake 5: Installation without system air venting
Air in the system destroys pumps mechanically (cavitation) and chemically (localized corrosion). After every installation, properly vent the system. More about installation can be found in the article Step-by-step installation of the Avansa circulation pump.
Practical examples from real customer cases
Example 1: Boiler room reconstruction in an older house (single-family house, 1970s)
The customer had an old cast iron boiler with natural circulation (no pump) and wanted to switch to forced circulation with a new condensing boiler. House area: 180 m², 10 radiators, longest branch approx. 18 m, DN 20 copper pipes. Boiler: 18 kW, temperatures 55/45 °C.
Calculation: flow rate = 18 × 860 / 10 = 1 548 l/h ≈ 1.55 m³/h. System resistance: piping approx. 2 m, boiler 1.5 m, radiators 0.8 m, total ≈ 4.3 m. Conclusion: AVANSA 25-6/130, stage II. The system works perfectly, the customer is satisfied.
Example 2: New construction, floor heating
New construction, 130 m², floor heating in three zones, regulation via thermostatic valve in each zone. Boiler 12 kW, temperatures 40/32 °C (ΔT = 8 °C). Flow rate = 12 × 860 / 8 = 1 290 l/h. System resistance including manifold ≈ 3.5 m.
We recommended AVANSA AUTO 25-4/180 E, because the thermostatic valves in individual zones change the hydraulic resistance of the network during the day. The electronic pump adapts to the changing resistance and prevents hydraulic noise, which would occur with fixed settings when some zones are closed.
Example 3: Replacement of a faulty pump, urgent repair
The customer calls in January: the pump has stopped, the house is cold. Old model: Grundfos UPS 25-40 with 130 mm center distance and 6/4" thread. Time is not on his side. AVANSA 25-4/130 is a compatible replacement with the same mounting dimensions – installation took 40 minutes and the system was running again.
Energy efficiency – what it costs you annually
A circulation pump usually runs 4 000 to 6 000 hours per year (depending on climate conditions and boiler regulation). An old, low-quality pump with a power consumption of 60–80 W consumes 240–480 kWh of electricity per year. At a cost of 0.22 €/kWh, this amounts to 53–106 € per year just for the pump.
Classic Avansa pumps have a power consumption in the range of 40–80 W depending on the stage and model – they are thus comparable to old pumps, but with better performance. The electronic AVANSA AUTO 25-4/180 E with an EC motor operates with a power consumption of 3–45 W depending on the current load. It thus consumes 12–270 kWh per year, which is a 50–80 % saving compared to an old pump under normal load. The return on the price difference compared to a classic model is typically 3–5 years.
What to do if you're still unsure
Pump sizing is not rocket science, but it can seem complicated at first. If you have the original project documentation of the house, you will find the heating network diagram in it, including the designed flows and losses – this is the most accurate basis. If you don't have the documentation, I recommend:
- Photograph the type plate of the boiler and the old pump.
- Measure the center distance of the old pump and identify the thread size.
- Estimate the length of the longest branch of the system (supply + return to the most distant radiator).
- Write to us or call us – with these details we will recommend a specific model for you.
Detailed instructions for setting up and the first start-up can be found in the articles Setting and flow regulation of the Avansa pump after installation and Installation of the Avansa circulation pump step by step. In case of any problems, there is also the article Common faults of Avansa circulation pumps and their solutions.
Avansa model comparison table
| Model | Max. H (m) | Max. Q (m³/h) | Center distance (mm) | Thread | Type |
|---|---|---|---|---|---|
| AVANSA 15-6/130 | 6 | 1.5 | 130 | 1" | Classic |
| AVANSA 25-4/130 | 4 | 2.5 | 130 | 6/4" | Classic |
| AVANSA 25-4/180 | 4 | 2.5 | 180 | 6/4" | Classic |
| AVANSA 25-6/130 | 6 | 2.5 | 130 | 6/4" | Classic |
| AVANSA AUTO 25-4/180 E | 4 | 2.5 | 180 | 6/4" | Electronic |
Frequently asked questions (FAQ)
Can I use Avansa in a system with domestic hot water (DHW)?
Avansa pumps are primarily intended for closed heating circuits. Some models are also suitable for domestic hot water circulation, but this must be verified in the technical documentation of the specific model. The main difference is in the materials, which must meet hygiene requirements for potable water. If you are unsure, contact us before purchasing.
What happens if I install a pump that is too powerful?
An oversized pump operates at an unsuitable point on its Q-H curve – either at high pressure and low flow (or vice versa, high flow and low pressure). The results are noise in the pipes (hissing, knocking), increased electricity consumption, faster bearing wear, and in some cases damage to thermostatic valves and seals due to excessive pressure. Oversizing is not a "safe choice" – it is a mistake.
How do I know that my old pump needs to be replaced?
The most common signs are uneven heating (some radiators are cold, others are hot), noise from the pump (grinding, squeaking, knocking), the pump does not start after the summer break (blocked rotor due to sediment), or simply increased energy consumption without an obvious reason. Pumps typically have a lifespan of 10–15 years under normal operation. More on diagnostics can be found in the article Common faults of Avansa circulation pumps and their solutions.
Is it necessary to drain the entire system when replacing the pump?
If there are ball valves installed on both sides of the pump (which should always be the case), it is sufficient to close the valves and drain only the water between them – a few liters. If there are no valves, you will have to drain the entire system – and use this opportunity to install the valves, saving you work in the future.
What is the difference between model 25-4 and 25-6?
The number before the slash (25) indicates the maximum flow in dm³/min, the number after the slash (4 or 6) indicates the maximum head in meters. Model 25-4 has a maximum head of 4 m, model 25-6 reaches 6 m. The flow capabilities are similar, but 25-6 overcomes higher hydraulic resistance – it is suitable for longer systems, complex networks, or installations with higher resistance from fittings. A detailed explanation can be found in the article What do the numbers in the name of the Avansa pump mean – performance, head and center distance.
Is it worth buying the electronic version of Avansa AUTO if I have a simple system without thermostats?
For a simple system with manually opened valves and no zonal control, the electronic version offers less benefit – the system does not change hydraulic resistance, so there is little for the adaptation to work with. Nevertheless, you will still save energy thanks to the lower power consumption of the EC motor. A detailed cost and comfort comparison can be found in the article Electronic vs. standard Avansa circulation pump – is it worth paying extra for the AUTO version.
Conclusion: a short selection process
Choosing the right Avansa circulation pump is not complicated if you proceed systematically. Find out the boiler's thermal output, calculate the required flow from it, and estimate the hydraulic resistance of your system. These two numbers will clearly determine which Avansa model is suitable for you. Then check the physical dimensions – the center distance and thread size – to ensure the pump fits mechanically. Finally, consider whether a classic three-speed solution is sufficient for you, or whether an electronic version is worth it in the context of your system.
The entire Avansa range covers typical family homes as well as larger buildings – from the compact AVANSA 15-6/130 for small systems to the electronic AVANSA AUTO 25-4/180 E for modern zonal systems with condensing boilers. The important thing is to choose the right model for your specific case – and this article was meant to help you with that.
Do you have a question on this topic?
Having trouble making a decision or dealing with a specific situation in your home? Write to us – we are happy to help.