TL;DR:
- Heat pumps work best at low flow temperatures (35–45°C), which makes them a natural match for underfloor heating — but only if the UFH system and floor construction can deliver enough heat output at those temperatures
- Screeded floors with wet UFH pipes are significantly more heat-pump-compatible than suspended timber floors with staple-up systems
- Retrofitting UFH into an existing home alongside a heat pump installation is possible but adds cost and disruption; some floor types rule it out entirely
- The Boiler Upgrade Scheme (£7,500 towards an ASHP) applies regardless of whether you have UFH — but your installer should assess whether your floor system is adequately sized for the new heat source
There’s a persistent myth in the heat pump world that goes something like: “install underfloor heating first, then the heat pump will work perfectly.” The reality is more nuanced. UFH and heat pumps do pair well in principle, but whether that pairing works in practice depends heavily on the construction of your floors, the insulation in your home, and how well the overall system is designed.
If you’re planning both changes at once — or wondering whether your existing UFH system is compatible with a heat pump upgrade — here’s what actually matters.
Why Heat Pumps and UFH Are a Natural Pair
Air source heat pumps are most efficient when the temperature difference between the outside air and the water they’re heating is small. That’s captured in the coefficient of performance (COP): a heat pump delivering water at 35°C on a mild day might achieve a COP of 4.0 (four units of heat for one unit of electricity). Push that flow temperature up to 55°C and the COP might drop to 2.5.
This matters because traditional radiator systems are sized to work with a gas boiler pumping water at 65–80°C. Underfloor heating, by contrast, typically runs at 35–45°C — sometimes lower. Because the heat is distributed across a much larger surface area (the entire floor), you don’t need the same intensity. That lower flow temperature is exactly where heat pumps are most efficient.
In a well-insulated home with properly sized UFH and a well-specified heat pump, the system can run at a COP above 3.5 year-round, keeping running costs competitive with gas (particularly with smart EV tariffs or Economy 7).
The Floor Construction Problem
Here’s where the gap between theory and practice opens up. Not all underfloor heating is equal.
Wet UFH in screed (ideal): Pipes embedded in a poured concrete or anhydrite screed are the best-performing floor type for low-temperature operation. The thermal mass of the screed stores heat efficiently and releases it slowly, smoothing out temperature fluctuations. These systems work well at 35–40°C flow temperatures and pair naturally with heat pumps.
Wet UFH in suspended timber (more challenging): Pipes installed between or beneath timber joists — common in older homes and retrofit projects — have much less thermal mass. Heat escapes upwards and downwards rather than being efficiently stored. To hit the same room temperature, you often need higher flow temperatures, which reduces heat pump efficiency. Insulating below the pipes helps significantly but adds cost and sometimes isn’t feasible with floor height constraints.
Electric UFH mats: Common in bathrooms and as a secondary comfort heat source. These aren’t relevant to heat pump integration — they run on electricity directly and operate independently of any water-based system.
Existing UFH originally sized for a gas boiler: Some homes have wet UFH that was installed and tuned for 50–55°C flow temperatures. At 35–40°C, the same pipe layout may not provide enough heat output on cold days. In this case, either the flow temperature needs to be raised (reducing heat pump efficiency) or the UFH needs to be supplemented or extended.
What “Properly Sized” Actually Means
Heat loss calculations determine how much heat your home needs on the coldest design day (typically -3°C in southern England, colder in Scotland). Your UFH system needs to be able to deliver that heat at the intended flow temperature.
For a heat pump at 40°C flow temperature to work:
- Floor coverage matters: higher pipe density and coverage percentage improves output per square metre
- Insulation above and below: upward efficiency (heat going into the room) should be 80–90%; good insulation beneath the slab is critical
- Room height and thermal mass: higher ceilings mean more heat loss; heavy thermal mass (concrete, stone) stores heat better than timber
A competent heat pump installer should run a room-by-room heat loss calculation and model whether the existing UFH can meet demand at the target flow temperature. If they don’t, that’s a red flag.
Retrofitting UFH: The Real Cost Picture
If your home doesn’t have UFH and you’re considering adding it as part of a heat pump installation, the costs vary substantially by floor type:
Ground floor screed retrofit: Depending on floor height constraints, this might involve lifting existing flooring, pouring a new screed with pipes, and waiting 4–8 weeks for the screed to cure before commissioning. Costs typically run £80–150 per square metre for the UFH element, plus flooring costs. Disruption is high — essentially a building project.
Upper floors: Almost always suspended timber construction in existing UK homes. Installing wet UFH requires either routing pipes through joist bays from below (disruptive) or using low-profile overlay systems (limited output capacity). Electric mats are sometimes used for top-up heat but shouldn’t be the primary heat emitter if you’re trying to run a heat pump efficiently.
Screed overlay on existing floor: In some cases, a thin (65–75mm) anhydrite screed can be poured directly over existing solid concrete or tile floors, adding UFH pipes. This only works if ceiling heights allow, and you’ll need to account for door clearances and transition strips.
Where Radiators Still Make Sense
Not every room needs UFH to make a heat pump work. Oversized radiators — designed for lower flow temperatures — can be a cost-effective alternative in rooms where floor works are impractical. As a rough guide, radiators need to be about 2.5x larger for 40°C than they would be for 70°C to deliver the same heat output.
Many retrofit heat pump installations use a hybrid approach: UFH on the ground floor (often easier to retrofit into older solid floors) and oversized radiators upstairs. This is a legitimate strategy and often more practical than attempting full-house UFH.
What to Expect From Your Installer
Before quoting, a good installer should:
- Carry out a full heat loss survey (MCS standards require this for the Boiler Upgrade Scheme application)
- Model system performance at different flow temperatures
- Assess whether existing emitters (UFH or radiators) are adequately sized
- Specify the UFH layout and flow temperatures to be verified during commissioning
The BUS grant (£7,500 for an ASHP) is available regardless of your emitter type, but installations that don’t pass MCS commissioning can have grants clawed back. An undersized system that can’t maintain design indoor temperatures in winter is a failure scenario you want to avoid.
The good news is that properly designed heat pump and UFH combinations genuinely perform well, reduce carbon emissions significantly versus gas, and can operate cheaply with overnight electricity tariffs. The not-so-good news is that “properly designed” requires more upfront analysis than many installers currently provide. Doing that analysis before signing anything is the most important step.