Circulating vs. Pumping Pumps: Differences, Advantages and When to Use Which
Circulation vs. Transfer Pumps: Differences, Advantages and When to Use Each
When a customer comes in saying they "need a pump for heating" or "want to pump water from a well," at first glance it seems like a simple request. In practice, however, there is a crucial technical difference hidden behind it that will determine whether the system will work reliably for years or start causing problems after the first season. Circulation pumps and transfer (transport) pumps are in fact completely different devices in terms of construction, function and application – despite the fact that both have a rotating impeller and move liquid.
In this article, we will in detail examine how these two categories differ, what their physical principles are, where each type has its justification and – what is most important in practice – how you can tell that you have chosen the wrong type. If you have not yet read our guide How to choose the right pump for heating or water: step by step, we recommend starting there; this article builds on it and goes deeper into specific types.
Basic principle: what exactly do both devices do
First, it is necessary to distinguish between two physical tasks that a pump can perform:
- Circulation: the liquid moves in a closed circuit, no large volumes are drained or added anywhere, the task of the pump is to overcome only friction (hydraulic resistances) of the piping and components in the circuit. The static pressure in the system is determined by the height of the water column and the expansion tank, not by the pump.
- Transfer: the liquid is physically moved from one place to another – from a well to a tank, from a tank to a consumer, from a low-lying place to a higher one. Here the pump must actually overcome gravity (geodetic height), the pipe's own resistance and sometimes also the vacuum at the suction side.
This distinction is crucial. A circulation pump is designed for the first task; a transfer pump (in various versions) for the second. If you mix them up, the result will not be catastrophic immediately, but the system will work inefficiently, the pump will wear out prematurely and energy consumption will be higher than it needs to be.
Circulation pumps: construction and principle
A circulation pump (English circulation pump, German Umwälzpumpe) is essentially a low-pressure centrifugal machine with a wet rotor. What does this mean in practice? The pump motor is directly immersed in the transported liquid – the bearings are lubricated and cooled by the water itself, the sealing is minimal (no mechanical shaft seal). This has consequences:
- Very quiet operation (typically 20–40 dB(A) at lower speeds)
- Practically maintenance-free operation with clean medium
- Not suitable for long periods of inactivity (bearings can "stick")
- Not suitable for medium with abrasive particles
The hydraulic part of a circulation pump is designed for small pumping heads (0.5–8 m water column) and relatively large flow rates. The performance curve (Q-H curve) is flat – the pump can handle various flows with minimal pressure change. This is exactly what a heating circuit needs: thermostatic valves on radiators open and close, the flow varies, but the pump must maintain a stable pressure in the system.
Modern circulation pumps are almost exclusively ECM (electronically commutated motor) – that is, with electronic speed control and automatic adjustment of power according to current needs. Such a pump consumes 5–45 W at full power (depending on size), but much less in regulated mode. Old single-speed pumps consumed 60–150 W at the same hydraulic power. If you still have an old type at home, see our article Pumps during heating renovation: replacing an old pump step by step – the return on investment for a new ECM pump is 2–4 years in a typical house.
When to use a circulation pump
- Central heating with a boiler (gas, oil, solid fuel, heat pump)
- Floor heating (large flows, low pressure difference)
- Solar thermal systems (collectors → tank)
- Systems with heat exchangers (e.g. heat recovery)
- Recirculation of hot domestic water (so that hot water comes out of the tap immediately without long waiting)
- Cooling circuits in industry (closed)
Pumping pumps: types, construction and principle
The term "pumping pump" covers a much wider range of equipment. In the context of households and small businesses, we most often refer to:
Surface pumps (self-priming)
They are installed in a dry place (in a technical room, in a pump shaft), water is sucked from below. The maximum suction height is physically limited by atmospheric pressure to about 7–8 m (practically 5–6 m under normal conditions). These pumps have a dry motor with a mechanical shaft seal – this is why they are noisier than circulation pumps, require occasional lubrication of the seal and have a significantly shorter lifespan when used incorrectly (dry running).
Typical example of use: a well with a water level at maximum 5 m below the pump, garden irrigation, a tank in a house, water removal from a basement during a flood.
Submersible pumps
The motor and hydraulics are submerged directly in water. There is no suction height limitation – the pump pushes the water up, it does not have to pull it. Submersible pumps for wells (drilled wells) can operate at depths of 20, 50, and even 100+ meters. The motor is either water-cooled (perforated) or hermetically sealed.
The diameter of the pump (most commonly 4" = 102 mm) must match the diameter of the drilled well. Note – a submersible pump for a well is a completely different product from a submersible sewage pump for pumping sludge or a flooded basement, although both are "submersible".
Pressure stations (hydrofor stations)
A pump (surface or submersible) combined with a pressure tank (membrane tank) and an automatic pressure switch. The result is a comfortable water pressure throughout the house without the pump running continuously. The pressure range is typically set to 1.5–3.0 bar or 2.0–4.0 bar depending on the need.
Drain and sewage pumps
A special category designed for contaminated liquids, sludge, flushes. The motor is dimensioned for harsh conditions, the impeller has large passages for impurities (solid particle passage 10–35 mm depending on the type). Do not use them as a replacement for circulation pumps – they operate on a completely different hydraulic principle.
Key technical differences at a glance
| Parameter | Circulation pump | Pumping pump |
|---|---|---|
| Type of system | Closed loop | Open system |
| Head | 0.5 – 8 m (s.l.) | 5 – 100+ m (s.l.) |
| Power | 5 – 45 W (ECM) | 250 W – several kW |
| Noise | 20 – 45 dB(A) | 45 – 70 dB(A) |
| Motor construction | Wet rotor | Dry rotor (surface) / wet (submersible) |
| Shaft seal | None (wet rotor) | Mechanical seal / hermetically |
| Q-H characteristic | Flat curve | Steep curve |
| Control | Frequency (ECM), continuous | Mostly on/off, pressure switch |
| Medium | Clean water, antifreeze mixtures | Clean water, contaminated (sewage type) |
| Maintenance | Minimal (practically none) | Seal check, filter (surface) |
Practical scenarios from everyday practice
Scenario 1: The customer wants a "heating pump"
This is the most common case. A house owner has a gas condensing boiler, 8 radiators on two floors and floor heating in the bathroom. The total water volume in the system is approx. 80–120 liters, the developed pipe length is 60–80 m. The hydraulic resistance of the system (with properly dimensioned pipes DN15–DN20) will be in the range of 1.5–3.0 m w.c. at the required flow rate of approx. 0.8–1.2 m³/h.
Solution: circulation pump with designation approx. 25-40, 25-60 or 25-80 (first number = flange diameter in mm, second = maximum head in dm). A modern ECM circulation pump of this type costs 80–200 € and consumes 5–25 W depending on the current load. See more in the article Pump performance and flow: how to calculate what you really need.
Scenario 2: The customer wants a "well pump"
A garden or dug well, water level approx. 3 m below ground, the house is 30 m from the well, garden area 1 000 m². Required flow rate 40–60 l/min for the garden, 10–15 l/min for the household.
Solution: self-priming surface pump with power 750–1 100 W, combined with a membrane pressure tank (minimum 20–50 liters) and pressure switch. If the water level drops below 5 m (e.g. in a dry summer), consider a submersible pump directly in the well.
Scenario 3: The customer has an old house where "the pump is noisy"
Classic case: a house from the 80s, original single-speed circulation pump, noise level 55–60 dB(A). The customer "tried to buy a transfer pump because the seller in the hardware store recommended it and it was cheaper". Result: the transfer pump has a dry rotor, mechanical seal, runs at 1 450 rpm and in a closed heating circuit produces even more vibrations and noise, because it was not designed for this purpose at all.
Correct solution: a modern ECM circulation pump with the same connection dimensions (Rp 1½", bolt spacing 130 mm, spacing 180 mm) – quiet, energy-saving, with automatic adjustment. More about noise in the article Pump noise: why it buzzes or vibrates and how to eliminate it.
Scenario 4: Solar thermal system
The customer installs solar collectors on the roof, a tank in the basement. The height from the tank to the collectors is 6 m, the hydraulic resistance of the collector loop is 1.5 m w.c. The medium is an antifreeze mixture (propylenglycol 40 %).
Solution: a special circulation pump for solar systems, which can withstand temperatures up to 110–130 °C and is compatible with glycol mixtures. A standard heating circulation pump would not last much longer here – the sealing and bearing lubrication of standard models are not certified for these conditions.
Scenario 5: Floor heating in a larger house
House 250 m², floor heating with 12 loops, each loop 80–100 m long from 16×2 mm pipe. The total hydraulic resistance of the circuit can reach 3–5 m w.c., required flow rate 2.5–3.5 m³/h. A small circulation pump 25-40 is not enough here – you need at least 25-80 or even 32-80.
Important: in such systems, balancing of the loops is practically always installed (balancing valves or regulating circuits), otherwise the shorter loops would "take" more than the longer ones and the house would not be heated evenly. This is also the reason why the pump alone is not enough – the entire system must be properly regulated. See Installation of a pump in a heating system: procedure and most common mistakes.
Parameters to pay attention to when choosing
Flow (Q) and head (H)
This is the basic pair of values you must know before any purchase. Flow is given in m³/h or l/min. Head (also "pump pressure" or "manometric head") is given in meters of water column (m w.c.) or in bars (1 bar ≈ 10.2 m w.c.).
For circulation pumps in heating, an approximate calculation applies: boiler power (kW) ÷ (4.18 × temperature difference in °C) × 3.6 = flow in m³/h. For a system with a 20 kW boiler and a temperature difference of 20 °C, we get approx. 0.86 m³/h. Hydraulic loss (H) must be calculated or estimated according to the length and profile of the pipes. This is discussed in more detail in the article Pressure and pumping height: what these parameters mean and why they are important.
Temperature and medium
Standard circulation pumps are designed for medium temperatures up to 110 °C (some up to 95 °C). Pumps for well water operate normally at 5–35 °C. Always check whether your application corresponds to the catalog values!
Connection dimensions
For circulation pumps, standard spacing is 130 mm (flanges Rp 1 and Rp 1¼) and 180 mm (flanges Rp 1½ and Rp 2). Most circulation pumps are interchangeable within the same spacing. For transfer pumps, the key is the suction and discharge nozzle (usually ½" to 2" or flanges DN25–DN80 depending on the power).
Energy efficiency class (EEI)
Since 2013, the ErP directive has been in force in the EU, according to which heating circulation pumps must meet EEI ≤ 0.23. Older pumps (EEI > 0.4–0.8) are significantly less efficient. When purchasing, look for a value of EEI as close to 0.20 or lower as possible – this means a truly modern ECM pump.
Most common mistakes and errors when choosing
Mistake No. 1: The customer installs a pumping pump into the heating circuit
This happens during renovations, when someone "improvises" with what they have at hand. A pumping pump with a power of 750 W in a closed circuit, where a 20 W circulation pump would be sufficient, creates a huge overpressure, or even cavitation (the water evaporates at some point, the impeller "strikes" air bubbles, the pump hums and vibrates). In addition, the energy consumption is 30–50 times higher than with the correct solution.
Mistake No. 2: Using a circulation pump to pump water from a well
A circulation pump on the suction side cannot create the necessary vacuum to lift water from a well. It has too low a head and is not structurally designed for suction lift. Result: the pump runs, but the water does not flow, because the pump cannot draw water from below.
Mistake No. 3: Too small or too large a pump
An over-dimensioned circulation pump in a small system operates at the most unsuitable point of its characteristic curve, produces noise (cavitation, turbulent flow), consumes unnecessary energy and wears out prematurely. An under-dimensioned one, on the other hand, cannot circulate water fast enough – radiators are cold, the boiler cycles in shorter cycles and is loaded inefficiently. More about the calculation can be found in the article Power and flow rate of the pump: how to calculate what you really need.
Mistake No. 4: Ignoring water quality
For pumping pumps for wells, the content of sand and mechanical impurities is crucial. Without filtration (sand trap, mesh filter 100–500 µm before the pump), the impeller and seal wear out prematurely. In old heating systems with circulation pumps, a similar problem occurs with sediments and corrosion products – when replacing an old pump, I always recommend flushing the system and installing a magnetic filter.
Installation and mounting: basic differences
Circulation pumps are installed in the heating system piping, always on the return pipe (cold side, lower temperature = longer bearing and seal life). The rotor axis must be horizontal (except for some ECM models approved for vertical mounting – always check the manual!). The direction of flow is indicated by an arrow on the body of the pump.
Pumping pumps – surface type – are installed in a technical room, firmly mounted, with a suction pipe sloping towards the well (to prevent air from settling). Before the first start-up, the pump must be filled with water (you pour it in through the lid or the appropriate opening) – dry running will destroy the mechanical seal even before the first start-up. A detailed procedure for circulation pumps is also in the article Mounting a pump in a heating system: procedure and most common mistakes.
Energy efficiency and operating costs
Here is the most marked difference between pump types. A circulation pump runs continuously throughout the entire heating season – that is 4,000–6,000 hours per year. An old 3-speed type with a power of 100 W consumes 400–600 kWh/year, which at a price of 0.20 €/kWh = 80–120 € per year. A modern ECM pump with a power of 5–25 W (average 15 W) consumes 60–90 kWh/year = 12–18 € per year. Savings of 60–100 € per year, investment payback in 2–4 years.
A pumping pump for garden irrigation runs only when in operation – in summer perhaps 300–500 hours per year. At a power of 750 W, this is 225–375 kWh/year = 45–75 €. There is less room for savings here, but choosing the right flow (not unnecessarily powerful pumps with huge losses when throttled) can save 20–30 %.
Lifespan and service
A quality circulation pump (wet rotor, ECM motor) has a lifespan of 15–25 years under the right conditions (clean water, correct temperature, correct point on the Q-H curve). An old type with bronze bearings and a mechanical seal lasts 8–15 years, but requires occasional seal replacement.
A surface pump for a well – lifespan depends very much on water quality. With clean water and correct installation, 8–12 years. With sandy or iron-rich water, significantly less. Submersible well pumps usually have a lifespan of 8–15 years; their disadvantage is that service requires pulling the pump out of the well (not trivial at depths of 30–50 m).
More about preventing faults and service intervals can be found in the articles Maintenance and service of pumps: how to extend lifespan and avoid failures and Common pump failures for heating and water: causes and solutions.
Special cases: where the boundaries are unclear
Recirculation of hot water (DHW)
This is a special case where a circulation pump is used in an almost "semi-open" system. Water circulates from the DHW tank through the whole house and back, so that hot water flows immediately from the tap. Technically, it is a closed circuit (tank → distribution → back to tank), but the water is potable and the pressure in the circuit is determined by the water supply pressure. Special small circulation pumps for DHW are used – they are certified for potable water (materials without copper and lead), have a power of 5–15 W and are equipped with a timer or presence detection.
Garden ponds and fountains
Submersible pumps of special design are used here – for turbid water, with the ability to pump larger amounts of impurities, quiet (since they are submerged in water). They are neither circulation nor classic pumping pumps – they form their own category of garden pumps.
Heat pumps
Modern air-to-water heat pumps have a built-in circulation pump for the primary circuit (refrigerant) and the secondary circuit (water). The secondary circuit (house) is always ensured by a classic circulation pump, sometimes directly integrated in the unit. When installing an external circulation pump, you must pay attention to compatibility with the integrated hydraulics of the heat pump.
Most frequently asked questions (FAQ)
Can I use a circulation pump to pump water from a garden or a container?
No. A circulation pump is designed to work in a closed circuit without gravitational load. It cannot create sufficient vacuum to suck up water and will not work efficiently even when "pushing" from a filled container – its head is too low (usually up to 8 m) and its hydraulic characteristic is not suitable for open systems. For transporting water from A to B, always choose the appropriate type of pumping pump.
Why is my circulation pump buzzing and what does that mean for choosing a new one?
A noisy circulation pump may indicate cavitation (air in the system), worn bearings, operation outside the optimal point on the Q-H curve, or too high a speed on the 3rd speed. When choosing a replacement, always choose an ECM model with smooth regulation – the pump will automatically adjust the correct speed and noise will drop significantly. A more detailed discussion of this topic is in the article Noise from the pump: why it buzzes or vibrates and how to eliminate it.
How many meters of water column does a typical family house need for heating?
For a typical family house (120–200 m² of living area, properly dimensioned piping DN15–DN20, 6–12 radiators), the usual hydraulic loss in the system is 1.5–4.0 m w.c. The pump does not need to be powerful in terms of head – flow is more important. As a rule of thumb: for every 10 kW of boiler power, calculate a flow of about 0.43 m³/h at ΔT = 20 K. The exact calculation can be found in the article Power and flow rate of the pump: how to calculate what you really need.
Is there a difference between a pump for potable water and technical water?
Yes, and it is important! Pumps intended for potable water must be made of materials approved for contact with potable water (stainless steel, certain types of plastics, without lead and cadmium). Standard circulation pumps for heating are not certified for this. Always look for the marking "suitable for potable water" (English: "potable water") or certification according to EN 12502, or WRAS (UK) or NSF (US).
Can I let a pumping pump run continuously?
Do you have a question about this topic?
Not sure or dealing with a specific situation in your household? Write to us – we are happy to help.