Heat pump with underfloor heating: water temperature, running costs and summer cooling
“Heat pump underfloor heating” is searched 480 times a month in the UK; in Spain “aerotermia suelo radiante” 1,600, in the Netherlands “warmtepomp vloerverwarming” 1,600, in Germany “Wärmepumpe Fußbodenheizung” 1,300. Underfloor heating and a heat pump are the pair that performs best. Here is why, what water temperature it needs, how rooms are controlled and what the floor does in summer.
Why they work well together
The floor heats a large surface with lukewarm water, and the cooler the water, the less electricity the heat pump uses. Our Kita X, for 1,000 kWh of heat over a season, uses 178 kWh of electricity with water at 35 °C and 228 with water at 55 °C, the radiator temperature. Why is explained in the article on how it works.
What temperature the water needs
Engineers often set the water at a fixed 35 °C, with a margin. But the floor is a mass of screed that stores heat, and much less is enough: in a home with underfloor heating that we follow, with electronics controlling by the rooms and the optimiser, the water runs at 23 °C in the morning and 27-28 °C in the evening. Running long and gently beats switching on and off. See the article on weather compensation and the one on the optimiser.
Rooms and circuits
Each room has its circuits on the manifold, and they must be balanced with the flow meters, as we explain in the article on balancing. With our units the underfloor zone is driven by the Floor board of the HCC electronics, with mixing valve, modulating circulator and actuators, and room sensors tell the unit how much heat is needed. The whole system is in the article on system control.
In summer the floor cools
In summer the same unit sends water at around 18 °C into the floor, above the dew point: the Kita X works at EER 4.88, against 3.21 with the 7 °C water of fan coils. The floor must not go below 19 °C and gives 45-50 W/m² of cooling, without blown air; for humidity a dehumidifier is needed. The full sum is in the article on cooling.
New build or renovation
In a new home underfloor heating and a heat pump are the most common choice. In a renovation it depends on how much depth can be removed; where the floor cannot be redone, the heat pump also works with radiators, as we explain in the article on radiators: ours reach 70 °C. The real limits are on the page on pros and cons.
Which unit
For flats and small homes we offer the Kita X, a 7.5 and 9 kW propane monobloc; for larger homes our new propane heat pump. The output is calculated for the house. For an opinion, ask us for information.
Frequently asked questions
Is underfloor heating good with a heat pump?
It is where a heat pump performs best: it works with lukewarm water. The Kita X uses 178 kWh of electricity for 1,000 kWh of heat with water at 35 °C and 228 with the 55 °C of radiators.
What water temperature for underfloor heating with a heat pump?
It is often set at a fixed 35 °C, but less is enough: in a home we follow, with room-based control, the water runs at 23 °C in the morning and 27-28 °C in the evening.
Can underfloor heating cool?
Yes, with water at around 18 °C above the dew point: the floor stays above 19 °C and gives 45-50 W/m². A dehumidifier is needed for humidity.
Should the heat pump be left on with underfloor heating?
It is better to let it run long and gently: the floor stores heat. Switching it on and off like a boiler makes it use more.
What if I cannot redo the floor?
The heat pump also works with radiators: ours reach 70 °C, and the water can often be much cooler.
Does underfloor heating need balancing?
Yes, circuit by circuit with the manifold flow meters: short circuits take more water than long ones.
See also: Fan coils with a heat pump: when to choose them, what water temperature they need and how they cool
All the technical tips are on the series page.
