Circulation pumps for underfloor heating

For professionals: How to choose a circulation pump for underfloor heating?

The starting point for the selection will be the resistance to flow. Therefore, it is important to keep in mind not to exceed certain loop length limits for a given pipe diameter.

In the case of the popular PEX diameter 16x2.0 mm, this value is approximately 120 meters per loop. Of course, it is possible to lay 250 meters of pipe or even 500 meters, but all at a certain cost....

A longer pipe means more hydraulic resistance, more resistance means a bigger pump, a bigger pump means more power consumption, a larger pump setting also means more flow noise in the pipes and on the control valves related to the pressure drop.

"Optimally long" underfloor heating loops will allow more comfortable operation of the entire system. The head of the circulating pump will be the result of calculating the resistance for the most unfavorable section, i.e. for example 120 meters for the longest loop (e.g. in the living room) + supply and return section.

Let us remember, not to add up the lengths of all loops.

If the pump provides the required flow for the most unfavorable section (the longest), it will also provide the flow for the shorter sections, as they have a lower resistance.

How much heating power we introduce into the floor will determine the output of the circulation pump. For example, let's consider a house with a heating surface of 140 m2 with 11 loops and a heating output of approximately 8 kW. In such a domestic underfloor heating system, if the system is designed accordingly, a constant differential pressure and 3 meters headroom are sufficient to operate all 11 loops (approx. 8 kW output).

Important to remember:

3 meters lift height will be necessary to achieve the flow rate calculated for our example (800 l/h).

A Wilo-Stratos PICO 25/1-4 pump for example operating in constant differential pressure mode should be good for such parameters.