Underfloor heating is usually the best heat emitter for a heat pump, because it can warm a room with water at around 35°C or below, which is the temperature range where a heat pump runs most efficiently. That does not make it the only good option. Correctly sized radiators can get close, and in some homes they are the more sensible choice.
This guide covers why underfloor heating (UFH) and heat pumps work well together, the difference between screed and low-profile systems, what retrofitting involves, how floor coverings affect output, and when radiators make more sense.
Why Does Underfloor Heating Suit a Heat Pump’s Low Flow Temperature?
Underfloor heating suits a heat pump because the whole floor acts as the emitter, so it can deliver enough heat from water at 35°C or lower where a radiator would need much hotter water. A heat pump’s efficiency falls as the flow temperature rises. The less it has to lift the temperature of the water, the more heat you get for each unit of electricity.
A radiator has a small surface area, so at low water temperatures it gives off much less heat than its catalogue rating. The MCS Heat Emitter Guide sets out how much bigger a standard radiator needs to be at each flow temperature.
| Flow temperature | MCS star rating | Radiator oversize factor (MCS Heat Emitter Guide) |
|---|---|---|
| Up to 35°C | 6 stars | 4.3 times rated output |
| 36–40°C | 5 stars | 3.1 times rated output |
| 41–45°C | 4 stars | 2.4 times rated output |
| 46–50°C | Below 4 stars | 2.0 times rated output |
| 51–55°C | Below 4 stars | 1.7 times rated output |
At 35°C, a radiator has to be more than four times the size you would pick for a boiler system. Few rooms have the wall space for that. A screeded floor with tiles, by contrast, reaches the 6-star band at 35°C in the MCS guide’s own example.
Grant’s UFH installation guide gives a useful reference point. A 16 mm pipe at 200 mm spacing, with a mean water temperature of 35°C, a room at 20°C and a floor covering of 0.1 m²K/W, delivers about 50 W/m². That is enough for most well-insulated rooms. Where heat loss is higher, tighter pipe spacing raises the output.
How Much More Efficient Is a Heat Pump With Underfloor Heating Than With Radiators?
A heat pump running at 35°C for underfloor heating can have a seasonal efficiency around 30% higher than the same unit running at 55°C for standard radiators. The exact gap depends on the model and the design temperature of the radiator system.
Manufacturer data shows the effect clearly. Mitsubishi’s 5 kW Ecodan R290 lists a seasonal coefficient of performance (SCOP) of 4.62 at 35°C and 3.53 at 55°C. Those are laboratory seasonal figures for an average climate, so real homes will differ, but the ratio between them holds.
For example, a home needing 10,000 kWh of heat a year would use about 2,165 kWh of electricity at a SCOP of 4.62, against about 2,833 kWh at 3.53. At Ofgem’s cap rate of 26.32p/kWh for October to December 2026, that difference of around 668 kWh is worth roughly £176 a year. This is illustrative only.
The gap is smaller against radiators designed for 45°C. That is why a well-designed radiator system can still perform well. The biggest efficiency losses come from undersized radiators forcing the flow temperature up to 50°C or 55°C.
What Is the Difference Between Screed and Low-Profile Underfloor Heating?
Screed UFH has pipes buried in a thick layer of sand and cement or liquid screed, while low-profile systems use thin boards or a thin levelling compound laid over an existing floor. Screed gives the most even heat and the best output at low temperatures. Low-profile systems are quicker to fit and raise the floor far less.
| System type | Typical build-up | Best suited to | Response |
|---|---|---|---|
| Sand and cement screed | 65 mm minimum over pipes (Nu-Heat); Grant recommends 75 mm, maximum 90 mm | New builds, extensions, floors being dug out | Slow; high thermal mass |
| Liquid (flowing) screed | 50 mm minimum | As above, with faster drying and better conduction | Slow, slightly quicker than sand and cement |
| Low-profile overlay (routed boards or thin screed) | About 15–18 mm | Retrofit over existing solid or timber floors | Fairly quick |
| Spreader plates between joists | Within the joist depth | Suspended timber floors, upstairs rooms | Quicker than screed |
Sand and cement screed needs a long drying period before floor coverings go down. Nu-Heat’s rule of thumb is one day per millimetre for the first 50 mm and two days per millimetre beyond that. Liquid screed can be dried faster with dehumidifiers. It is also dense, so it conducts heat well, which helps a heat pump run at a lower temperature.
Nu-Heat’s thinnest overlay is 15 mm and its dry board option is 18 mm. Some lower-output versions will not suit a heat pump in a room with high heat loss. The system must be chosen against the room-by-room heat loss figures, not simply on thickness.
Can You Retrofit Underfloor Heating in an Existing Home?
Yes, you can retrofit underfloor heating in an existing home, most easily with a low-profile overlay system or during a renovation where the floor is already coming up. The main limits are floor height, insulation beneath the pipes and cost.
How Much Floor Height Does Retrofit Underfloor Heating Need?
An overlay system usually needs about 15–18 mm plus the floor finish, while a screed system needs a full new floor build-up including insulation. A rise of 15–18 mm affects door bottoms, thresholds, skirting and kitchen plinths. It gets harder where floor levels have to match adjoining rooms or step down to an external door.
If you are digging out a solid ground floor anyway, a full screed system with insulation is often the better long-term choice. On suspended timber floors, spreader plates fitted between the joists avoid raising the floor at all.
What Insulation Is Needed Under Underfloor Heating?
Insulation is always needed under UFH pipes, otherwise a large share of the heat goes down into the ground or the structure. Nu-Heat’s guidance is 70 mm of PIR on ground floors and 30 mm of PIR or equivalent on floors above heated rooms. Grant’s guide sets a minimum thermal resistance of 0.75 m²K/W for intermediate floors and aims to limit downward losses on ground floors to 10 W/m².
Overlay systems laid on an uninsulated concrete slab are the weak point. They can work, but the downward loss reduces what reaches the room. Joisted timber floors being retrofitted should be insulated below the deck.
How Much Does Retrofit Underfloor Heating Cost?
Wet underfloor heating costs roughly £95–£110 per m² installed in a renovation, according to Checkatrade’s 2026 cost guide. That excludes the heat pump itself and any major floor works.
| Scenario (Checkatrade, 2026) | Wet UFH cost |
|---|---|
| New build, per m² | £85–£100 |
| Renovation, per m² | £95–£110 |
| New build terraced house, 75 m² | About £6,375 |
| New build semi-detached, 90 m² | About £7,650 |
| Retrofit terraced house, 75 m² | About £7,125 |
Budget separately for making good, such as new floor finishes and trimming doors. The Boiler Upgrade Scheme grant of £7,500 in England and Wales goes towards the heat pump installation. It is not a separate pot for underfloor heating.
Which Floor Coverings Work With Underfloor Heating and a Heat Pump?
Tiles and stone work best with underfloor heating and a heat pump, followed by engineered wood, vinyl and laminate, while carpet works only if the combined tog of carpet and underlay stays low. Every floor finish adds thermal resistance. The higher the resistance, the warmer the water has to be to push the same heat into the room, and the lower the heat pump’s efficiency.
UFH designed to the European standard BS EN 1264 typically assumes a maximum floor covering resistance of 0.15 m²K/W, which is 1.5 tog. Nu-Heat says carpet and underlay together should never exceed 2.5 tog, and preferably stay below 1.5 tog with a heat pump.
| Floor covering | Suitability with a heat pump | What to check |
|---|---|---|
| Ceramic tile, porcelain, stone | Best | Flexible adhesive and grout rated for UFH |
| Engineered wood | Good | Manufacturer’s UFH approval and maximum surface temperature |
| Vinyl, LVT, laminate | Good if thin | Thin, UFH-rated underlay; surface temperature limit |
| Carpet | Acceptable with care | Carpet plus underlay ideally below 1.5 tog, never above 2.5 tog |
| Thick felt, rubber crumb or cork underlay | Poor | Avoid; swap for a low-tog UFH underlay |
Floor surface temperature is also capped for comfort. BS EN 1264 sets maximums of 29°C in occupied areas, 33°C in bathrooms and 35°C in perimeter zones. A system designed around 35°C water rarely gets near those limits.
If you plan to change a floor finish later, tell your installer at the design stage. Moving from tiles to thick carpet can push the required flow temperature up and cost efficiency for the life of the system.
Can You Have Underfloor Heating Downstairs and Radiators Upstairs?
Yes, underfloor heating downstairs with radiators upstairs is one of the most common heat pump layouts, and the Energy Saving Trust notes that installers sometimes recommend it to reduce cost and disruption. The design needs care so the radiators do not drag the whole system up to a higher flow temperature.
A heat pump produces one flow temperature at a time. If the upstairs radiators need 50°C to heat the bedrooms, the heat pump has to produce 50°C and the UFH circuit then mixes that down. The downstairs rooms stay comfortable, but the heat pump runs at the less efficient temperature.
The better approach is to size the upstairs radiators to work at the same low temperature as the floor, or close to it. Bedrooms are often kept cooler and have lower heat loss, so larger or double-panel radiators at 40–45°C are usually achievable. Where the two circuits really need different temperatures, a mixing valve on the UFH manifold or two separately controlled heating zones will be needed.
Under MCS design rules, the installer calculates heat loss room by room and must tell you the design flow temperature leaving the heat pump before any blending valves. If that figure is set by one or two awkward rooms, ask whether upgrading those emitters would lower it for the whole house.
How Quickly Does Underfloor Heating Respond, and How Should You Control It?
Screed underfloor heating responds slowly, taking around an hour to heat up even with a boiler and longer at heat pump temperatures, so it works best with a heat pump when run steadily on weather compensation rather than switched on and off. Timber and low-profile systems respond faster because there is less mass to heat.
Slow response is not a problem with a heat pump. Heat pumps prefer long, steady running at low output. A screed floor stores heat and releases it evenly, which smooths out the heat pump’s cycling. The mistake is to treat it like a boiler with timed bursts. Large overnight setbacks mean the floor cools, then the heat pump has to run harder and hotter in the morning to recover.
| Control approach | Works well with UFH and a heat pump? | Notes |
|---|---|---|
| Weather compensation | Yes | Flow temperature follows outdoor temperature; keeps water as cool as possible |
| Small overnight setback | Yes | Keeps the floor warm enough to recover gently |
| Room thermostats as limiters | Yes | Stops overheating in sunny rooms without fighting the compensation curve |
| Timed on/off like a boiler | No | Forces higher flow temperatures to recover |
| Zoning every room to separate schedules | Usually not | Too many closed zones can reduce flow and cause short cycling |
Our engineers set the compensation curve at commissioning and fine-tune it once cold weather arrives.
When Are Radiators the Better Choice for a Heat Pump?
Radiators are the better choice when fitting underfloor heating would mean major floor works, a big rise in floor height or thick carpet you want to keep. In those homes, well-sized radiators designed for 45°C or lower are cheaper to install and cause far less disruption.
Radiators also make sense in these situations:
- Upstairs rooms with suspended floors and fitted carpet, where UFH would add cost for little gain.
- Rooms used for short periods, such as a spare bedroom, where faster response helps.
- Period properties where original floors or joists cannot be disturbed.
- Homes where the existing pipework and wall space allow larger radiators to replace the current ones easily.
Swapping a few key radiators for larger models is usually far cheaper than whole-house UFH. In some retrofits, that change alone brings the design flow temperature down into the 4-star or 5-star band.
Is Underfloor Heating Worth Adding When You Install a Heat Pump?
Underfloor heating is worth adding with a heat pump when the floor is being replaced anyway, such as in an extension, a new build or a ground-floor renovation. The extra cost is then small compared with the efficiency and comfort it gives over the life of the system.
| Your situation | Usual recommendation |
|---|---|
| New build or new extension | Screed UFH, ideally liquid screed |
| Ground floor being dug out and insulated | Screed UFH downstairs, low-temperature radiators upstairs |
| Solid floors staying in place, some height available | Low-profile overlay in main living areas |
| Carpeted suspended floors, no planned works | Upgraded radiators sized for 45°C or lower |
| Listed or period home with original floors | Radiators, possibly with a few larger or fan-assisted models |
Whichever emitters you choose, the heat pump will only be as efficient as the design behind it. If you would like us to look at your home, a HomeKOG survey includes a room-by-room heat loss calculation and a clear recommendation on UFH, radiators or a mix of both.
