How to choose a circulation pump for heating – what to focus on
How to choose a circulation pump for heating – what to really focus on
The circulation pump is the heart of every modern heating system. Without it, hot water from the boiler would simply not reach the radiators, floor heating, or the hot water storage tank. Despite this, most people give it minimal attention when choosing – they buy "some kind of pump" and later deal with problems: noise, insufficient circulation, high electricity consumption, or premature failure. In practice, we see that a poorly chosen pump can disable even a well-designed system.
This article will guide you through all the key parameters and considerations you should take into account before buying a circulation pump – whether you are replacing an old one or dealing with a new build. This is not theory for theory's sake: each chapter includes specific numbers, examples from real customer cases, and practical recommendations.
Why pump selection is more important than it looks
A typical family house with an area of 150 m² has a component in the circulation pump that runs 24 hours a day, 7 days a week, for six to eight months a year. Over 10 years, that is approximately 17,000 to 23,000 hours of operation. With older pumps of class C or D, this means a consumption of 60–100 W continuously, i.e., 1,000–2,000 kWh per year just for the pump. A modern pump of class A consumes 5–25 W at the same performance – the difference is dramatic, and the return on investment in a better quality unit is measured in years, not decades.
Energy consumption is not the only factor – hydraulic suitability also plays a role: an under-dimensioned pump will not push water through long circuits or through floor heating with small pipe diameters. An over-dimensioned pump, on the other hand, creates unnecessary noise, can open safety valves, and causes hydraulic imbalance – some radiators are hot, others are cold.
Hydraulic parameters – flow and head as the basis of calculation
Before buying a pump, you must know two key hydraulic parameters: flow (Q) and head (H). Without these numbers, you are moving blindly. If you are looking for a more detailed explanation, we cover them in detail in the article Hydraulic parameters of a circulation pump: flow, head and power.
How to calculate the required flow
Flow depends on the thermal power of the system and the temperature difference. The basic formula is:
Q = P / (c × ρ × ΔT)
where P is the boiler power in kW, c is the specific heat capacity of water (4.18 kJ/kg·K), ρ is the density of water (~1 kg/l), and ΔT is the temperature difference between the supply and return. For classic heating at 70/50°C (ΔT = 20 K) and a 15 kW boiler, Q ≈ 645 l/h, which is approximately 0.18 l/s. For a condensing boiler with a 55/45°C mode (ΔT = 10 K), the flow would be double – around 1,300 l/h. These numbers are a practical starting point.
How to determine the required head
Head (delivery height, expressed in meters of water column, m w.c., or in Pa/kPa) must overcome the hydraulic resistance of the entire pipe network. A simplified estimate for classic radiator heating: 0.5–1.5 m w.c. for every 10 meters of the longest circuit, plus the resistance of thermostatic valves (0.5–2.0 m w.c.) and other fittings.
For a family house with the longest circuit of 30 m, you realistically need a head of 3–6 m w.c. Floor heating has higher resistance – typically 2–4 m w.c. per manifold, depending on the length of loops and pipe diameter. You choose a pump so that its operating point (the intersection of the pump and system curves) lies in the middle third of the pump's Q-H curve – this is the zone of highest efficiency.
Energy class – save hundreds of euros over the lifetime of the pump
Since 2013, the EU ErP (Energy-related Products) regulation has banned the sale of C-class and worse pumps for heating systems. Since 2015, only A-class pumps can be sold. Despite this, older stocks or pumps intended for industrial use, where different rules apply, still appear on the market. If you are buying a pump today, look for energy class A and an EEI (Energy Efficiency Index) value lower than 0.23.
What does this mean in practice? An old pump with a power consumption of 80 W, during an 8-month heating season (5,856 hours), consumes 469 kWh per year. At an electricity price of 0.22 €/kWh, this amounts to 103 € per year just for the pump. A modern pump with a power consumption of 8–15 W consumes 47–88 kWh per year, which is 10–19 €. The difference of 80–90 € per year accumulates to 1,200–1,350 € over the 15-year lifetime of the pump. For more information on this topic, see the article Energy class of circulation pumps – what A, B, C means and how much you can save.
Dimensional compatibility – shaft distance and connection
This is a technical detail that causes the most problems during renovations. When replacing an old pump with a new one, you need to maintain the shaft distance (the distance between the centers of the inlet and outlet ports). The most common values are 130 mm and 180 mm. The thread diameter is typically G 1½" or G 2".
If you buy a pump with a shaft distance of 130 mm, but the distance at your location is 180 mm, you have a problem – either you need to add intermediate fittings (reducers, S-shaped fittings), or you need to choose a pump with the correct dimensions. Today, there are pumps with adjustable shaft distances (e.g., 130–180 mm), which is a big advantage for renovations. All relevant dimensions are discussed in detail in the topic Dimensional compatibility of circulation pumps – shaft distance and connection.
Type of heating system – not every pump is suitable everywhere
Radiator heating
Classic radiator heating with steel or cast iron radiators has relatively low hydraulic resistance (if the system is properly balanced) and operates with outlet temperatures of 55–75°C. Most standard pumps with a head of 4–6 m w.c. and a flow rate of 500–1,500 l/hour are sufficient here. Problems arise in older homes where the piping system is neglected, full of sludge and lime deposits – in such cases, the resistance is higher, and we always recommend chemically cleaning the system before installing a new pump.
Floor heating
Floor heating is a specific discipline. The pipes are thinner (typically PE-Xa or PE-RT, diameter 16–20 mm), the loops are long (60–120 m), and the overall system resistance is significantly higher. A distributor with 8–12 circuits can have a total resistance of 5–8 m w.c. In addition, the temperatures are low (35–45°C), which is an advantage for condensing boilers. Therefore, choose a pump with a higher head (min. 6–8 m w.c.) for floor heating, and make sure that the heat pump or boiler to which you connect it can handle low temperature differentials.
Combined systems and hot water tanks
If the system also includes heating of a hot water storage tank (Domestic Hot Water – DHW), it is necessary to either use a separate circuit with its own pump (a clearly better solution from a hydraulic perspective) or properly overdimension a three-way mixing valve and a common pump. In practice, we see that customers try to "save on a pump" and end up investing in service or a second pump. A correct design from the beginning saves time and money.
Heat pumps
Heat pumps (air-to-water, ground-to-water) are sensitive to pumps – they require a constant flow and low temperature differential. Most modern heat pumps have an integrated circulation pump for the primary circuit, but the distribution circuit to radiators or floor heating requires its own pump. In this case, an automatic proportional (Δp-v) or differential pressure (Δp-c) mode is especially important so that the pump can adapt to closed thermostatic valves.
Manual vs. automatic mode – modern pumps can think for themselves
Old pumps had three manual speed settings – you chose setting 1, 2, or 3 and let the system run. Modern pumps with electronically commutated motors (EC motors) offer several automatic modes:
- Constant pressure (Δp-c): the pump maintains the same differential pressure at all times, regardless of flow. Suitable for large systems with long pipe runs.
- Proportional pressure (Δp-v): the pump reduces pressure in proportion to the drop in flow (when thermostatic valves are closed). Ideal for most single-family homes with thermostatic valves on radiators.
- Constant temperature (AutoAdapt): the pump automatically analyzes the system and selects the optimal performance. Highest comfort, minimal user intervention.
- Night reduction and hourly program: some pumps allow programming of reduction during the night or absence, which further reduces consumption.
From practice: in new buildings with well-regulated thermostatic valves, we recommend the Δp-v (proportional pressure) mode. In older homes without thermostatic valves, manual settings or Δp-c are more suitable. Pump adjustment is discussed in the article Adjusting a circulation pump after installation – manual vs. automatic mode.
Pump brand – Grundfos and Wilo vs. others
It is impossible to avoid the topic that customers often ask: "Do I need to buy Grundfos or Wilo, or is a cheaper brand sufficient?" The short answer: it depends on the context and your priorities. A longer answer deserves a whole article Less known circulation pump brands vs. Grundfos and Wilo – is it worth it?, but we will summarize the basic principles.
Grundfos (a Danish manufacturer) and Wilo (a German manufacturer) are among the market leaders and are a safe choice if you want certainty, long warranty, availability of spare parts, and a service network. Their pumps are tested under extreme conditions and have decades of development behind them. The price is accordingly higher – entry-level models start around 80–120 €, and premium electronically controlled models reach 200–400 €.
Less well-known brands – and here we also include other brands available on atria.sk – can provide sufficient performance at a lower price. The key is to verify: energy class (at least A), declared EEI index, availability of technical documentation (Q-H curves, performance graphs), and warranty conditions. A pump that has CE certification, declared parameters, and is delivered with a manual in Slovak or Czech is fundamentally different from a "no-name" product without documentation from an anonymous source.
In practice, we see that for recreational buildings, garden huts or less demanding simple radiator circuits, less well-known brands are a reasonable economic choice. For heat pumps, complex systems with multiple circuits or for customers who do not want to have problems for 15 years, an investment in a premium pump makes sense.
What to pay attention to during installation
Although this topic is discussed in more detail in the article Installation of a circulation pump – procedure, orientation and most common errors, a few key points should be emphasized here as well:
- Orientation of the rotor axis: most modern pumps are designed for horizontal mounting (horizontal rotor axis). Some models allow for vertical mounting as well, but always check the manual – mounting in the wrong position can cause noise, overheating or reduced lifespan.
- Position in the system: the pump is usually installed on the output (hot) pipe after the boiler, before the heating system. Some systems requiring separation of circuits require different placement – always according to the project documentation.
- Air vent: every pump must have the possibility to bleed air in its vicinity. Air in the system is the main cause of noise and cavitation.
- Filter/sediment trap: always install a sediment trap (mesh filter) before the pump. Dirt is the main cause of premature wear of the impeller. This is especially true for the renovation of old systems.
- Closing valves: ball valves must be installed on both sides of the pump so that the pump can be replaced without draining the entire system.
Noise from the pump – when is it normal and when does it indicate a problem
Modern pumps with wet rotors (which is the vast majority of pumps for heating in family homes) should run almost unnoticed. Typical noise levels are 25–40 dB(A) depending on the power. If you can clearly hear the pump throughout the apartment or it produces vibrations and squeaking, something is not right.
The most common causes of noise are air in the system (popping, bubbling), cavitation (sharp whistling – the pump is operating outside its working point), foreign objects in the impeller (scratching), or worn bearings (constant humming). Air can be removed by bleeding, cavitation needs to be addressed by changing the settings (reducing speed or increasing static pressure in the system), and other problems indicate a fault. More in the article Common circulation pump faults and how to recognize and fix them.
Pump lifespan and maintenance
A well-chosen and properly operated pump should last 15–25 years. The main factors that shorten its lifespan: corrosive medium (bad pH of water, oxygen content), mechanical impurities (missing filter), unsuitable mounting position, long-term operation outside the working point, and summer shutdown without preparation.
Recommendations for extending lifespan: during summer shutdown, run the pump for a few minutes at least once a month to prevent the rotor from seizing (bearings of a wet rotor are lubricated with water – they can seize when completely turned off). In the autumn before the heating season, check the pH and hardness of the water in the system – ideal pH is 7.5–9.0, hardness maximum 1–2 mmol/l. A detailed guide to bleeding and regular inspection can be found in the article Maintenance and bleeding of a circulation pump – how to extend its lifespan.
Practical scenarios from practice – how to decide in specific situations
Scenario 1: Replacing an old pump in a family house from 1990
The customer has a masonry house of 160 m², a natural gas boiler of 20 kW, 10 radiators, steel pipes of ¾" and 1". The original pump Sigma (three speed levels, power 80 W) has failed. Solution: a pump with an axial distance of 130 mm, thread G 1½", head 4–6 m w.c., flow up to 1 200 l/h, energy class A. Before installation: chemical cleaning of the system and installation of a sediment trap. After installation: setting of proportional pressure (Δp-v), medium setting of the head. Result: quiet operation, consumption dropped from 80 W to about 12 W.
Scenario 2: New construction with underfloor heating and a heat pump
A bungalow of 120 m², air-to-water heat pump with an integrated pump on the primary circuit. Distribution circuit: 8 underfloor heating loops, total pipe length about 600 m (PE-Xa 17×2 mm). Pressure drop at the distributor and circuits: about 7 m w.c. Solution: a pump with a head of at least 8 m w.c., flow 800–1 000 l/h (at ΔT = 5 K and heat pump power of 6 kW), automatic Δp-v or autoAdapt mode. Important: low noise (the pump is in a technical room close to the living area), EEI < 0.20.
Scenario 3: A cabin with a simple circulation circuit
A cabin of 60 m², a wood-burning boiler of 12 kW, 5 steel radiators. The system is simple, without thermostatic valves, hydraulically balanced manually. Here it is not economically sensible to invest 250 € in a premium pump – a solid pump of class A for 60–90 € with manual setting of speed level 2 is sufficient. Energy savings will be modest (pump consumption is low during short seasons), but energy class A and manufacturer reliability are important.
Most frequently asked questions (FAQ)
How do I find out what pump I have in my system and how to replace it?
On the pump body, there is typically a nameplate with the name, performance range (Q/H), and dimensions (shaft distance, thread diameter). If the label is unreadable, measure the shaft distance between the centers of the flanges (usually 130 or 180 mm), note the thread diameter, and use photo documentation to confirm the type of connection. With these details, you can find a compatible replacement model or consult with a sales representative. Further practical information can be found in the topic Common questions about circulation pumps from less well-known brands.
Can I use a larger pump than calculated – "just to be safe"?
This is not a good idea. An oversized pump operates on the left side of its Q-H curve, where efficiency is low and noise levels are high. In addition, with fully open thermostatic valves, it can create excessive pressure, causing humming in the piping and at the thermostatic valves. We choose a pump so that the operating point lies in the optimal zone of the curve – not at the maximum.
Is it worth buying a pump with Wi-Fi or Bluetooth connectivity?
For a standard family home with a simple series heating system, smart connectivity is a "nice to have," not a necessity. If you have a smart home system or want to monitor the pump's consumption and status remotely, this feature can be useful. Basic pumps with automatic proportional or pressure-controlled performance are sufficient for 90% of installations without any additional user intervention.
What to do if the system still doesn't heat properly after replacing the pump?
There can be several reasons: incorrect pump setting (you may need to increase the head or flow), air in the system (bleed the system), clogged thermostatic valves, or deposits in the pipes. First, try bleeding the system – this is the most common cause of poor circulation after service. If that doesn't help, check the pump settings (level, operating mode) and compare the actual pressure with the residual pressure the pump generates.
How long does it take to replace a circulation pump?
An experienced heating technician can replace a pump (with shut-off valves) in 30–60 minutes, including bleeding the system. If the valves are corroded or you also need to replace fittings, expect 2–4 hours. We recommend performing the replacement outside the heating season to avoid potential complications in case of a water leak.
Is it necessary to connect the pump via a thermostat or can it run continuously?
Modern electronically controlled pumps have their own control logic and can automatically reduce performance to a minimum. It is not technically necessary to switch them with an external thermostat, although connecting them to the boiler's control system or thermostat allows the pump to be completely turned off when the boiler is not firing – which further reduces energy consumption. Most installations in family homes have the pump directly connected via boiler automation.
Conclusion – investing in the right pump pays off
Selecting a circulation pump is not rocket science, but it's also not something you should handle carelessly. Once you calculate the flow and head based on the real parameters of your system, check the dimensions, and choose a model with energy class A and a suitable control mode, you've already completed 90% of the selection. The remaining 10% consists of proper installation, bleeding, and setting – the factors that make the difference between a pump that quietly and efficiently runs for 20 years and one that you notice every morning.
If you're unsure about the calculations or compatibility, check other topics in our Knowledge Center – for example, Hydraulic parameters of a circulation pump: flow, head, and power, where you'll find detailed calculation procedures, or Installation of a circulation pump – procedure, orientation, and common mistakes for a practical installation guide.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us – we're happy to help.