Low-temperature radiator
Low-temperature radiators emit enough heat even at low flow temperatures. It is often sufficient to replace individual critical radiators.
- 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.
Classic radiators were designed for oil and gas boilers with high flow temperatures. Their nominal output is often specified for a 75 °C flow and 65 °C return. With a heat pump, however, the water should be significantly cooler. Low-temperature radiators have a larger surface area, more fins or built-in fans for this purpose, so that they emit enough heat even with lukewarm water.
Why this is important for your house
The lower the flow temperature, the more efficient the heat pump. klimaaktiv writes that even a targeted radiator replacement can lower the flow temperature by a few degrees and save operating costs in the long term.
Do I have to replace all radiators?
Usually not. According to klimaaktiv, existing radiators in older buildings can often continue to be used because they were generously dimensioned in the past, especially if the house has since been insulated. The decisive factor is the least favourable room: the radiator that is smallest in relation to the heating load of the room determines the required flow temperature for the entire house. If you replace this specific radiator, the temperature drops for everyone.
How to proceed
- Have the room-by-room heating load calculated.
- Check the output of the existing radiators at a low flow temperature.
- Only replace the bottlenecks and then carry out a hydraulic balancing.
klimaaktiv offers a heating capacity calculator for this. The Flow temperature guide provides more background information.
Related terms
Flow temperatureSurface heating (underfloor and wall heating)Hydraulic balancingHeating load
Sources