How to choose a circulation pump for heating

Heating systems are divided into systems with natural (gravitational) and forced circulation. In systems with forced circulation, the installation of a circulation pump is mandatory. Its task is to ensure the movement of the coolant through the system at a given speed. And in order for it to cope with its task, it is important to choose the right circulation pump. 

Purpose and types

As already mentioned, the main task of the circulation pump is to ensure the required speed of the coolant through the pipes. For systems with forced circulation, only under such conditions will the design capacity be reached. During the operation of the circulator, the pressure in the system increases slightly, but this is not its task. It’s more of a side effect. To increase the pressure in the system, there are special booster pumps.

There are two types of circulation pumps: dry and wet rotor. They differ in design, but perform the same tasks. To choose the type of circulation pump you want to install, you need to know their advantages and disadvantages.

Dry Rotor

It got its name due to the design features. Only the impeller is immersed in the coolant, the rotor is in a sealed housing, it is separated from the liquid by several sealing rings.

These devices have the following properties:

• They have a high efficiency – about 80%. And this is their main advantage.
• Require regular maintenance. During operation, solid particles contained in the coolant enter the sealing rings, violating the tightness. To prevent depressurization and maintenance is required.
• The service life is about 3 years.
• During operation, they emit a high level of noise.

Such a set of characteristics is not very suitable for installation in heating systems of private houses. Their main advantage is high efficiency, which means less energy consumption. Therefore, in large networks, circulation pumps with a dry rotor are more economical, and they are mainly used there.

wet rotor

As the name implies, in this type of equipment, both the impeller and the rotor are in the liquid. The electrical part, including the starter, is enclosed in a metal sealed glass.

This type of equipment has the following properties:

• The efficiency is about 50%. Not the best indicator, but for small private heating systems this is not critical.
• Maintenance is not required.
• Service life – 5-10 years, depending on the brand, mode of operation and condition of the coolant.
• During operation, they are almost inaudible.

Based on the above properties, it is not difficult to choose a circulation pump by type: most stop on devices with a wet rotor, as they are more suitable for working in an apartment or a private house.

How to choose a circulation pump

Each circulation pump has a set of technical characteristics. They are selected for the parameters of each system individually.

We select technical characteristics

Let’s start with the selection of technical characteristics. There are a lot of formulas for professional calculation, but to select a pump for the heating system of a private house or apartment, you can get by with averaged norms:

• The performance of the pump is taken equal to the power of the installed heating boiler. That is, if the boiler is 35 kW, then the pump is selected with a capacity of 35 l / min.
• Next, you need to calculate the required pressure (lift height). On average, it is believed that for 10 meters of the pipeline there should be a pump head of 0,6 m. To determine what head of the circulation pump is needed for the system, its total length must be divided by 10 and multiplied by 0,6 m / s. For example, if the total length of the heating system is, for example, 80 m, the required pressure will be: 0,6 m * 8 = 4,8 m. That is, in the technical specifications, the pressure should not be less.
  

• It is better if the speed of the coolant in the system can change. This will make it possible to adjust the heat transfer depending on the temperature outside: the higher the speed, the more heat is transferred. Therefore, it is better to choose models that can operate at several speeds. But in any case, the speed of the coolant should not exceed 1,6 m/s. This is the threshold for silent operation of the heating system, if you accelerate the coolant faster, noise will appear.
• The electrical power of the circulation pump is selected depending on the diameter of the pipes. The smaller the cross section of the pipe, the greater the hydraulic resistance it has. That is, for systems diluted with pipes of small diameter, more powerful pumps are required.

Choosing a circulation pump for heating following these rules is easy. Calculations are elementary. But I must say that these figures are average. If your house at some point is very different from the “average”, you need to make adjustments either upward or downward technical characteristics. For example, you have well insulated the house, the capacity of the previously purchased boiler turned out to be excessive. In this case, it makes sense to take a pump with a lower capacity. In the opposite situation – it is chilly in the house in extreme cold – you can put a more productive circulator. It will temporarily solve the problem (in the future it is necessary either to insulate or change the boiler).

Model selection

When choosing a specific model, pay attention to the graph with the pressure characteristic of the pump. On the graph, you need to find the point at which the values ​​​​of pressure and productivity intersect. It should be in the middle third of the curve. If it does not fall on one of the curves (there are usually several of them, characterizing different models), they take the model whose graph is closer. If the point is in the middle, take the less productive one (the one located below).

What else to pay attention to

In the technical characteristics of circulation pumps, there are several more positions that you should pay attention to. The first is the allowable temperature of the pumped medium. That is, the temperature of the coolant. In quality products, this indicator is in the range from +110°C to +130°C. In cheap ones, it can be lower – up to 90 ° C (and in fact 70-80 ° C). If your system is designed as a low-temperature one, this is not scary, but if there is a solid fuel boiler, the temperature to which the coolant can be heated is very important.

It is worth paying attention to the maximum pressure at which the pump can operate. In the heating system of a private house, it is rarely higher than 3-4 atm (this is for a two-story house), but normally it is 1,5-2 atm. But still, pay attention to this indicator.

What else to pay attention to is the material from which the case is made. The optimal one is cast iron, the cheaper one is made of special heat-resistant plastic.

Connection type and size. The circulation pump can be threaded or flanged. The thread can be external and internal – appropriate adapters are selected for it. Connecting sizes can be: G1, G2, G3/4.

It is also worth paying attention to the presence of protection. May be dry run protected. In circulation pumps with a wet rotor, it is very desirable, since the cooling of the motor occurs due to the medium being moved. If there is no water, the motor overheats and fails.

Another type of protection is overheating protection. If the motor heats up to a critical value, the thermal relay turns off the power, the pump stops. These two features will extend the life of the equipment.

How and where to install a circulation pump read here.

Manufacturers and prices

When choosing manufacturers of a circulation pump, the approach is the same as when choosing any arc equipment. If possible, it is better to take equipment from European manufacturers that have been on the market for a long time. The most reliable circulation pumps in this sector are Willo (Willo), Grundfos (Grundfos), DAB (DAB). There are other good brands, but you need to read reviews on them.

Please note that all specifications are for moving water. If the coolant in the system is a non-freezing liquid, adjustments must be made. For relevant data for this type of coolant, you will have to contact the manufacturer. Similar characteristics could not be found in other sources.