Tips for choosing and using circulator pumps

The circulator pump is a very important element in heating, air conditioning, hot water, and also in floor heating systems. Thanks to the pump, the coolant circulates in the “closed” heating system, the “warm floor” system, which increases the heat transfer. When using a pump, smaller pipelines can be mounted, hence reducing the amount of coolant in the system, reducing the consumption of energy, and reducing the cost of the materials used, although it needs to be additionally installed. Such heating systems respond more quickly to temperature fluctuations and are easier to adjust. The use of circulator pumps in heating systems saves up to 30% of the energy used to heat the coolant. Pumps for hot water supply (DHW) allow you to maintain a constant temperature of water in hot water systems (recirculation of hot water). When choosing a circulator pump, it is necessary to consider where the pump will be used in the heating system or hot water supply. Structurally, the pumps have a clear division into pumps for heating and domestic hot water. The pump housings for heating systems are made of cast iron, and for hot water use housings made of bronze or brass. Circulator pumps for heating systems with a wet rotor. They work continuously throughout the heating season, so they are faced with high demands: silent operation, low power consumption, simplicity and reliability.

Pump Performance

Flow Rate

To determine the flow rate in the heating system, the following formula is used:

Q = Qn / 1,163 * Δυ (m 3 / hour)

Q   – pump flow at the design point in [m3 / h]

Qn    – boiler thermal power in [kW]

1,163   – specific thermal capacity of water [W * h / kg * K]

Δυ   – the calculated temperature difference in the direct and return pipelines of the heating system, in kelvins [K], while 10 to 20 K for standard systems can be taken as a basis.

Pump Head

In order to deliver the pumped coolant anywhere in the heating system, the pump must overcome the sum of all the hydraulic resistances. Since it is usually difficult to determine the laying pattern and the conditional passage of pipelines, for the approximate calculation of the pressure of the heating system, you can use the following formula:

H = R * L * ZF / 10,000 (m)

R   – friction losses in pipes [Pa / m]. At the same time, one can take as a basis a value of 50 Pa / m – 150 Pa / m for standard systems (depending on the year the house was built, in older houses due to the use of pipes of a larger diameter, the pressure loss is less (50 Pa / m)).

L – length [m] of direct and return pipelines or: (house length + house width + house height) x 2

Zf- coefficient. for valves ≈1.3, thermostatic valve ≈1.7, mixer ≈1.2

In the presence of shut-off valves and thermostatic valves, the coefficient must be used ZF = 2.2 .

In the presence of shut-off valves, thermostatic valves and a mixer, the coefficient must be used ZF = 2.6 .

10000   – conversion factor (m) and (Pa)

Example: a boiler installed in an old-built apartment building has a capacity of 50 kW.

For the temperature difference Δυ = 20 K (feed temperature = 90°C, return temperature = 70°C) it turns out that the pressure is: Q = Qn / 1,163 * Δυ (m3 / h) = 50 / 1,163 * 20 = 2,15 m3 / h

When heating a similar building with a lower temperature difference (for example, 10 K), the circulator pump must provide a double flow rate, i.e. 4.3 m3 / h, provided that the heat produced by the heat generator can reach the consumers in the required amount.

The pressure loss due to friction in the pipeline in our example is 50 Pa / m,

the total length of the direct and return pipelines is 150 m, the coefficient is 2.2, since there are no mixer and thermostatic valves. As a result, we obtain the pressure (H): Н = R * L * ZF / 10000 (m) = 50 * 150 * 2.2 / 10000 = 1.65 m.

Mounting Methods

Circulator pumps for heating systems can be mounted directly on the pipeline in horizontal or vertical position, provided that the axis of the pump shaft must always be horizontal. They can be mounted both on the giving, and return pipelines. It is preferable to install on the return pipe. The arrow on the pump housing for heating systems indicates the direction of movement of the coolant. Before and after the circulator pump, it is necessary to install shut-off valves or valves of the same diameter as the conditional passage of the pump. Cranes or gate valves are used for convenient maintenance of the pump during maintenance or repair. In this case, the coolant does not need to be drained from the heating system or hot water supply. Between the shut-off valve and the suction pipe of the pump, it is absolutely necessary to mount a coarse filter of the same diameter as the conditional passage of the pump. If several circulator pumps are used in the heating system, check valves must be installed on each of them. The valve is installed of the same diameter as the nominal bore of the pump and is mounted after the pump on the discharge pipe to the shut-off valve. If the axis of the motor shaft is mounted vertically,

relative to the horizon, during operation, an air plug may form in the upper part of the separation cup. A ceramic or graphite bearing will not be lubricated by the pumped liquid, which can lead to overheating and, as a consequence, jamming of the rotor shaft. As we have already said, lubrication of bearings of pumps with a “wet rotor” is carried out by the pumped liquid. In addition, stator cooling will deteriorate due to insufficient fluid circulation. To do this, the fluid through the separation cup must circulate constantly. More details on installation methods can be found in the installation and operating instructions for circulator pumps for heating systems.

The point at which the characteristics of the circulator pump and the system intersect is called the operating point of the system and the pump. This means that at this point there is a balance between the useful power of the pump and the power necessary to overcome the resistance of the heating system. The pump head is always equal to the system resistance. The supply that the pump can provide also depends on the pressure. It must be remembered that the feed must not be lower than a certain minimum. Otherwise, poor performance can cause a strong temperature rise in the pump chamber, which can damage the pump. To avoid this, follow the instructions of the pump manufacturer’s factory. An operating point outside the pump performance may cause overheating and failure of the pump. When the flow rate changes during pump operation, the pressure changes, and, consequently, the operating point is constantly shifted. Finding the design operating point in accordance with the requirements when operating the system in maximum mode is the task of the designer. All other operating points are located to the left of the calculated operating point.

Offsetting the operating point of the system to the left of the calculated operating point increases the pump head. This will lead to increased noise in the heating system in the presence of control valves and valves.

Maintenance and repair

Circulator pumps for heating systems with a “wet” rotor cannot be operated without a coolant duct – overheating of ceramic or graphite bearings and, as a result, jamming of the rotor may occur.

To reduce noise in closed heating / cooling systems with circulator pumps, it is necessary that there is no air in the system. Automatic air valves or are used to remove air.

In practice, it very often happens that the coolant contains a fine suspension and scale. When the pump is operating, the scale is gradually deposited and overlays on the working surfaces of the rotor and the separation cup. The distance between the rotor and the cup is 0.1-0.2 mm, due to the accumulation of scale, the rotor “wedges” in the cup. If the pump with the “stuck” rotor is energized for a long time, this defect can lead to more serious damage: overheating and short circuit of the windings. The stator fails, as the coolant flow is reduced or completely stopped, and the engine is not sufficiently cooled. Unfortunately, the engine rewinding workshops do not take the stators of household circulator pumps into operation, because of their high complexity and complexity in re-setting, as a result – the purchase of a new pump. If the stator of the pump has not failed, then it takes a lot of time to wedge the rotor: from several hours to several days. This procedure is especially difficult with pumps with a ceramic shaft. The shaft of such pumps is very fragile and can break due to careless movement. As a rule, it was possible to wedge out all the rotors that fell into the repair with such a defect.

To reduce scale in the heating system, you must:

  • Flush the heating system before commissioning. Especially a lot of scale is formed in heating systems operating on the “natural” coolant circulation, since it was very often necessary to add water to expansion tanks, and this water was not prepared. After installing a circulator pump in such a system and poorly flushing the heating system, all the scum that had been layered over the years in pipes and radiators with slow natural circulation very quickly appeared in the pump due to the fact that the coolant speed increased several times.
  • Fill the heating system with special softened water.
  • Do not drain the coolant from the system after the end of the heating season.
  • After the end of the heating season, it is necessary to turn on the pump for 1-2 minutes at least once a month, so that at the beginning of the heating season there is no problem with jamming of the rotor.
  • Install in the heating system

The second reason for the failure of the pumps is the presence of suspended matter in the heating system. The suspension enters the ceramic bearings, and production is produced on the bearings and the shaft (this is especially fast on graphite bearings). Due to generation, there is a backlash and additional noise, and at one fine moment, the rotor “sticks” to the cup. Simply put, the rotor stops spinning. There are practically no spare parts for circulator pumps, and you have to buy a new pump. To prevent such defects, it is necessary to follow the same procedures as when jamming the rotor.


If you need a circulator pump, when choosing it, you should pay attention to the main characteristics: performance, coolant temperature, noise level, how much electricity it consumes and the pump size as well.

It is necessary to clarify the temperature of the pumped liquid and correlate it with similar characteristics of the unit, as well as the type of coolant – water or antifreeze.

Wet rotor circulator pump has very low noise (up to 45 dB) and vibrations. To understand that the pump is working, you can only put your hand on it.

When considering the issue of energy consumption, it should be borne in mind that some of the most modern pumps consume less energy than a conventional light bulb. In addition, the automatic regulation of heating devices will help you save energy. In this case, the circulator pump will operate intermittently. A special sensor will show when the coolant temperature has dropped below the set line and will start the pump.

Another factor that is often very important to the user is the installation size of the device. This is the size of the circulator pump. It is meticulously considered if the pump is planned to be embedded in an existing pipeline, while ensuring a neat and inconspicuous installation. The circulator pumps for domestic use usually have a pump body of 130mm or 180mm length with a thread connection size of 1” or 1 1/2” or 2” diameter. Larger pumps have flanged connections.

Summing up, we can say that modern heating systems, both in individual and in urban buildings, need high-quality pumping equipment that can provide effective circulation of the coolant. For a long and reliable operation, it is necessary to comply with the installation conditions and operating rules. The pumps used must meet very stringent requirements: be economical, reliable and provide continuous operation during the heating period for many years.