How do we choose a pump for underfloor heating?

The recirculation pump for the underfloor heating system or so-called pump for the underfloor heating mixing group is produced by a multitude of suppliers. The most popular brands of recirculation pumps locally are Wilo, Grundfos or Dab.

Regardless of the supplier, we have to determine two very important parameters that define the characteristics of a recirculation pump.

Each water pump has two parameters that define its operating curve: flow rate and pumping height. The pumping flow rate is expressed in cubic meters per hour and the pumping height is expressed in meters water column.

What is the variable speed recirculation pump?

The recirculation pump is a water pump with low energy consumption, which works permanently in a pressurized heating or cooling system. Its role is to transport the heat agent from the source to the consumer. The new generation of recirculating pumps with variable speed incorporates a frequency converter in their construction that can vary the rotor speed depending on the needs for greater energy efficiency.

How do we determine the flow of water needed to carry a lot of energy?
The flow determination is very simple to do, we must use the following formula:

Flow m = Q / (c * dT)

where Q is the power in W, dT is the temperature difference between return / return, and c is a constant with the value of 1.163.

Thus, if we intend to choose a recirculation pump for a floor heating circuit and we want to transport 3000 W to a dT of 5 degrees C we have a flow rate Q = 3000 / (1,163 * 5) = 515 liters / h.

If we intend to transport the same amount of energy for a circuit with heaters at a dT of 15 C we have a flow rate Q = 3000 / (1,163 * 15) = 172 liters / h. Which we have to convert into cubic meters of water per hour.

How do we determine the pumping height?

This is a very important parameter to consider. The correct determination of this parameter is not very simple.

Things get much more complicated with this parameter. Many times I happen to hear even the so-called “specialists” that the required pumping height is equal to the height of the house.

We must keep in mind that in the case of closed pressurized systems the height of the installation is not related to the pumping height of the recirculation pump expressed in meters by the water column.

The pumping height is actually the ability of the pump to push the fluid with sufficient pressure to overcome the frictional pressure losses of the fluid relative to pipes, bends, tees, fittings, valves, heat exchangers, etc. to the farthest point of the return / return installation.

This also depends on the flow, the diameter of the pipes, the temperature and the density of the fluid.

For a domestic application of heating in the floor a recirculation pump with an available 6 meters water column is sufficient.

To find out exactly the required pumping height, you need to have a floor heating project.

Can the floor be heated without a pump?

Heating in general cannot be done without using a recirculation pump. I think this question generally refers to the question whether or not a pumping group is located on the floor heating distributor?

It is not necessary to use a recirculation pump located on the distributor but my recommendation is to use a larger recirculation pump and not the one from the condensing boiler.

If you do not use an additional recirculation pump this can be considered a mistake. You can see the top floor heating mistakes here

How much current does a recirculation pump consume?

Since 2016, the new ErP standards in the field of energy efficiency have changed radically. Even though the recirculation pumps consumed relatively little, here we speak of the domestic ones. We speak especially of those mounted on conventional thermal power plants, these pumps consumed up to a maximum of 130 W per hour.

Looking at the European level, millions of recirculation pumps are installed and the cumulative energy consumption of inefficient recirculation pumps is very high.

Since 2016 the obligation to use high efficiency pumps, equipped with frequency converter, has been introduced on the market. New size-based recirculation pumps can consume up to a minimum of 3 W per hour, depending on size.

Where is better to instal the recirculation pump?

The re circulation pump can be mounted both on the flow or on the return. The recirculation pump cools with the fluid transported, which is why the idea that it would be better to install it on the return side, because the heat is cooler.

The latest generation pumps can be mounted on the flow or on the return without any problems. The materials from which they are built have a very wide operating limit.

As a general rule, it is better for the pump to be mounted in the flow for the circuits where the injection is made, such as the one for underfloor heating.

In the construction of thermal power plants it is mounted on the return. In solar panel systems, the pump is mounted on the cold return of the boiler.