Surface heating (underfloor and wall heating)
A surface heating system emits heat over large areas such as the floor or wall. It manages with low flow temperatures and is a good match for a heat pump.
- Flat curve, typical for underfloor or wall heating: low flow temperature even in frosty conditions.
- Steep curve, typical for radiators: when it is cold, a significantly higher flow temperature is required.
- The flatter and lower the curve, the more efficiently the heat pump runs.
With a surface heating system, water-carrying pipes are laid in the screed, in the wall or, less commonly, in the ceiling. Because the surface area is large, lukewarm heating water is enough to warm the room. Exactly what a heat pump likes: the lower the flow temperature, the less electricity it needs for the same amount of heat.
Why this is important for your house
klimaaktiv lists surface heating systems, alongside low-temperature radiators, as a good prerequisite for a heat pump. The Energieinstitut Vorarlberg considers the ideal flow temperatures for heat pumps to be below 35 °C, which is easily achievable with underfloor heating in well-insulated houses.
The screed as a storage medium
An underfloor heating system stores heat in the screed. The klimaaktiv guide gives a rule of thumb: 1 m² of floor corresponds to a water storage tank of around 10 litres (at a 5 K temperature difference). This helps to bridge utility blocking times and make use of solar power. This storage effect should be taken into account when planning a buffer tank.
Setting the heating curve correctly
Flat heating curves apply to underfloor heating systems. The klimaaktiv guide to hydraulic balancing gives guide values according to the year of construction, such as a base point of 23 °C and a slope of 0,15 for houses built from 2020 onwards. Your installer will make the precise adjustment.
In older buildings without underfloor heating, low-temperature radiators are often the alternative. Find out more in the flow temperature guide.
Sources
- klimaaktiv Wegweiser zur guten Installation von Wärmepumpen (klimaaktiv Guide to Good Installation of Heat Pumps, BMK, 2020) (accessed on 4 October 2026)
- klimaaktiv guide to hydraulic balancing (BMK, 2023) (accessed on 4 October 2026)
- Energieinstitut Vorarlberg: Die Wärmepumpe, eine Glanzleistung an Effizienz (Energy Institute Vorarlberg: The Heat Pump, a Masterclass in Efficiency) (accessed on 4 October 2026)