The heat pump does not need a specific type of heating – it needs low flow temperatures. Underfloor heating provides them inherently and is the ideal case; however, generously dimensioned radiators also go a long way, and low-temperature radiators close the gap in individual rooms. A conversion to underfloor heating is almost never a prerequisite. (As of: July 2026)
Key points in brief
- The deciding factor is not the radiator or floor, but the flow temperature: the lower it is, the more efficiently the heat pump works.
- Underfloor heating is the ideal partner – large surface area, low temperature, and the floor stores heat like a silent buffer.
- Radiators are better than their reputation: many existing systems are generously dimensioned and run hotter than necessary out of habit.
- The middle way is called low-temperature radiators: more surface area or quiet fan support – specifically in the one or two critical rooms.
- The practical test on the existing heating system usually answers the system question without an expert report.
Why heat distribution determines efficiency
A heat pump raises ambient heat to heating temperature – and the smaller this lift, the less electricity it needs. The source (air or ground) determines the lower end of the lift; the upper end determines your heat distribution: the flow temperature with which the heating water is sent into the floor or radiators. This is exactly where the annual performance factor is decided – and thus the electricity bill for the next twenty years.
The rule behind this is simple and applies to every heating surface: The larger the surface area that emits heat, the lower the water temperature can be. An entire floor emits the same heat at a significantly lower temperature than a small radiator under the window. Everything else in this guide is just the application of this one sentence.
Underfloor heating: the ideal partner
Surface heating is built for the heat pump, even if it is older than it: the entire floor works as a heating surface, the necessary flow temperature is low, the heat pump runs in the most efficient range. New builds have therefore combined the two as standard for years.
In addition, there is an underestimated side effect: the floor structure stores heat. This inertia, which is considered a disadvantage when quick temperature changes are desired, is a gift for the heat pump – it can run long, quiet cycles instead of frantic pulses, and in combination with a solar system, the floor can be «charged» at midday with your own electricity, which lasts until the evening. The house itself becomes a heat accumulator, without anyone buying a battery.
The honest downside: exactly this inertia. Anyone who spontaneously wants two degrees more in the evening waits longer with underfloor heating than with a radiator. In the everyday life of a constantly temperature-controlled apartment, this hardly matters – you should just know it.
Radiators: better than their reputation
The prejudice «heat pumps need underfloor heating» persists stubbornly – and is false in this absoluteness. What is correct is: radiators need higher flow temperatures than surface heating systems. But «higher» does not by any means mean «too high», and for two reasons.
Firstly, many existing houses were built with generously dimensioned radiators – often more and larger than the room actually needs. Secondly, quite a few houses have received new windows or insulation over the years, without anyone ever updating the heating curve: The heating system runs hot out of habit, not out of necessity. Large radiators plus reduced heat demand together result in exactly what the heat pump wants – lower flow temperatures, without anyone having to rebuild anything.
Whether your house is one of them is clarified by the simplest test in the whole industry: lower the flow temperature of the existing heating system on a trial basis during a cold winter and observe whether it remains comfortable everywhere. If it does, the radiator question is answered – without an expert report, using your own house as a test bench.
Low-temperature radiators: the targeted middle way
Almost always, it is not all rooms that limit, but one or two critical ones – typically the bathroom or the room on the weather side. For exactly these cases, there is the middle way: low-temperature radiators. They perform the same as their predecessors at a significantly lower water temperature – either simply through more surface area and more fins or through quiet fan support that actively increases heat emission. The opposite direction would be a unit that delivers the high temperature itself – what that costs in operation is written in the article on the high-temperature heat pump.
The charm of this solution lies in its scale: instead of rebuilding the house, you specifically replace the one or two limiting radiators – a small intervention with a big leverage on the flow temperature of the entire system. Together with hydraulic balancing, which allocates exactly its water volume to each radiator, this brings many existing houses over the heat pump threshold without a full renovation being necessary.
Conversion to underfloor heating: when it is worthwhile – and when it is not
The complete switch to surface heating is the most thorough solution – and the most complex: floors out, pipes in, new structure. As pure heat pump preparation, this is rarely proportionate in inhabited houses; the targeted measures above achieve a large part of the effect for a fraction of the effort.
The calculation looks different if renovations are taking place anyway: during a core renovation or floor replacement, the step to surface heating is small, and then it is almost always worthwhile – the lowest flow temperature, the best annual performance factor and the storage effect of the floor come essentially as a bonus. Mixed forms are also completely normal: underfloor heating on the renovated ground floor, radiators on the upper floor – the heat pump can serve both, even with different temperature levels if planned correctly.
The comparison at a glance
| Underfloor heating | Existing radiators | Low-temperature radiators | |
|---|---|---|---|
| Flow temperature | low – ideal case | depending on dimensioning, often lower than expected | low, deliberately lowered |
| Efficiency (APF) | best | good to sufficient – practical test will show | almost at surface heating level |
| Effort | Conversion – only makes sense during renovation | none | replace individual radiators |
| Response | slow, stores | fast | fast |
| Typical case | New build, core renovation | Existing building with generous radiators | Existing building with 1–2 critical rooms |
Qualitative classification, As of: July 2026 – the decisive factor is the design for the specific building.
The system question is almost always put to us as an either-or – «do we have to tear out the floors first?» – and the answer is almost never an either-or. The typical project in the region looks like this: the practical test over a winter shows that three quarters of the house have long been suitable for a heat pump; the bathroom and a corner room facing north are limiting. Two low-temperature radiators are installed there, plus hydraulic balancing – and the flow temperature of the whole system drops to a level for which nobody has opened a floor. The reverse case also happens: anyone who is renovating the floors anyway and then asks whether surface heating is «additionally» worthwhile gets a clear yes from us – that is the one moment when the big conversion is small.
Frequently asked questions
Do I have to convert to underfloor heating for a heat pump?
No – the conversion is almost never a prerequisite. The deciding factor is the necessary flow temperature, and this can often be lowered sufficiently with generous existing radiators, targeted low-temperature replacements and hydraulic balancing. The practical test on the existing heating system provides the answer for your own house.
Does a heat pump work with old cast iron radiators?
Often yes – old cast iron radiators are frequently generously dimensioned and emit heat evenly thanks to their mass. The age of the radiator is not a criterion; its surface area in relation to the heat demand of the room is.
What exactly are low-temperature radiators?
Radiators that deliver the same performance at a low water temperature – through significantly more emission surface area or through quiet fans that actively increase heat emission. They are used specifically in the rooms that would otherwise force the flow temperature of the entire system upwards.
Can I mix underfloor heating and radiators?
Yes, this is common and can be solved cleanly from a technical point of view – for example, surface heating on the renovated ground floor and radiators above. Correct hydraulic planning is important; if well designed, the heat pump can serve both circuits.
Can underfloor heating be retrofitted?
Yes – in the course of a floor or core renovation, the step is small and worthwhile. As an isolated individual measure just for the heat pump, however, it is rarely proportionate; in this case, targeted radiator measures are the more economical route.
Free initial consultation
Your radiators can do more than you think.
We check heat distribution and flow temperature at your house and tell you honestly what is sufficient: existing stock, targeted replacement – or the surface area after all. Free of charge and without obligation.
Prefer to talk? +41 78 830 83 35
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Sources: Fachvereinigung Wärmepumpen Schweiz FWS (system basics of heat distribution); empirical values from the planning and project practice of ecoEn GmbH, Zurich region.
Last updated: 9 July 2026 · Author: ecoEn editorial team
