The short answer
Heat pumps work best at low flow temperatures, and the heat emitter you pair them with affects efficiency. Underfloor heating (UFH) spreads heat over a large surface, so it runs at the lowest flow temperatures (often around 35°C), which lets the heat pump achieve its highest efficiency and gives very even, comfortable warmth. Radiators can absolutely work with a heat pump, but because they have a smaller surface they usually need to run a little hotter, or be upsized, to deliver the same heat at low flow temperatures. UFH is ideal in new builds and ground-floor renovations but is disruptive and costly to retrofit into existing floors. For most UK retrofits, correctly sized radiators are the practical choice; many homes use UFH downstairs and radiators upstairs. Both can give an efficient heat pump system when designed properly.
A heat pump is only as efficient as the system it feeds. The emitter — underfloor heating or radiators — has a big influence on how low the flow temperature can go, and therefore on efficiency and comfort. Here is how they compare.
Underfloor vs radiators with a heat pump
- UFH flow temperatureLowest (often ~35°C)
- Radiator flow temperatureHigher, or upsize radiators
- UFH efficiencyHighest (large surface area)
- Radiator retrofitEasier and cheaper than UFH
- Common UK approachUFH downstairs, radiators upstairs
Why flow temperature is the key
A heat pump's efficiency rises as the flow temperature falls — the cooler the water it has to produce, the more heat it delivers per unit of electricity. The emitter determines how cool that water can be while still keeping the room warm, because it has to release enough heat at the chosen temperature.
Underfloor heating uses the whole floor as a radiator. That huge surface area means it can warm a room with water at a low temperature — often around 35°C — which lets the heat pump run at or near its best efficiency. Radiators have a much smaller surface, so to release the same heat they either need hotter water or need to be larger. This is why radiator systems for heat pumps are often designed with bigger or additional radiators: it lets them run at low flow temperatures and keep the heat pump efficient.
| Factor | Underfloor heating | Radiators |
|---|---|---|
| Surface area | Whole floor (large) | Small per unit |
| Typical flow temp | Lowest (~35°C) | Higher, or upsize to lower it |
| Heat pump efficiency | Highest | Good with correct sizing |
| Comfort | Very even, gentle warmth | Even with good design |
| Retrofit ease | Disruptive and costly | Easier and cheaper |
| Response time | Slower to warm/cool | Faster |
Indicative comparison for guidance. Sources: Energy Saving Trust; MCS.
Comfort, response and running cost
Underfloor heating gives a very even, gentle warmth across the whole floor and is invisible — no radiators on the walls. Because it heats a large thermal mass, it responds slowly: it takes longer to warm up and to cool down, which suits the steady, continuous way heat pumps are best run.
Radiators respond faster, warming a room more quickly when called for. With a heat pump they are designed to run at lower temperatures than a gas system would use, so they stay warm rather than hot to the touch. Comfort with correctly sized radiators is good; the system simply heats more gently and steadily than a traditional high-temperature boiler setup.
Cost, floor build-up and combining both
Cost is a major practical divider. Adding or upsizing radiators is comparatively cheap and quick. Retrofitting underfloor heating means either lifting existing floors to lay pipes and screed, or using a low-profile overlay system that raises the floor level — both more expensive and disruptive, and the raised floor can affect door heights and thresholds. In a new build or where floors are already being replaced, that cost largely disappears, which is why underfloor heating is so common in new construction.
Floor finishes also interact with underfloor heating. It works very well under tile and stone, which conduct heat readily; carpet and thick underlay insulate the floor and reduce output, so floor coverings need to be chosen with the heating in mind. Radiators are indifferent to floor finishes.
Many homes use both. A frequent pattern is underfloor heating on a new or renovated ground floor — where the slab is being worked on anyway — with radiators upstairs, where lifting bedroom floors would be impractical. Designed together, the two can share the same heat pump, with the system set to run at the lowest flow temperature both emitter types can deliver, keeping efficiency high throughout.
What works best for a UK retrofit
In a new build or a deep renovation where floors are coming up anyway, underfloor heating is an excellent partner for a heat pump and lets it run at its most efficient. The added cost is far easier to absorb when the floor is already being worked on.
For an existing home, radiators are usually the pragmatic choice. An MCS-certified installer carries out a room-by-room heat loss survey and sizes the radiators so the system runs at a low flow temperature. Many existing radiators are already large enough; others are upsized. A common hybrid approach is underfloor heating on a new or renovated ground floor with radiators upstairs. Either way, the goal is the same: keep the flow temperature low so the heat pump operates efficiently while keeping every room comfortable.
Frequently asked questions
Do I need underfloor heating for a heat pump?
No. Heat pumps work well with radiators, provided they are correctly sized to deliver enough heat at a low flow temperature. Underfloor heating allows the lowest flow temperatures and highest efficiency, but radiators — sometimes upsized — are the practical choice for most retrofits and still give an efficient, comfortable system.
Will my existing radiators work with a heat pump?
Often, yes, though some may need to be larger. Because a heat pump runs at lower flow temperatures than a gas boiler, radiators must release enough heat at that lower temperature. An MCS installer's heat loss survey checks each room and upsizes only the radiators that need it, keeping the flow temperature low and the heat pump efficient.
Is underfloor heating more efficient than radiators with a heat pump?
Generally yes, because its large surface area lets the heat pump run at the lowest flow temperatures, which maximises efficiency. But the difference is modest when radiators are correctly sized, and retrofitting underfloor heating into existing floors is costly and disruptive — so well-sized radiators are usually the sensible retrofit choice.
Sources & further reading
- Energy Saving Trust — air source heat pumps
- MCS — heat pump system design and installers
- Heat Geek — flow temperature and emitter sizing
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.