UK Home Extension: R290 Heat Pump with Wet Underfloor Heating
This real UK home-extension project shows an R290 air-to-water monobloc heat pump paired with wet (hydronic) underfloor heating as a low-temperature heating system. Site photographs document the pipe layout, seven-circuit manifold, screed installation and outdoor heat pump. The result is a practical reference for installers, developers and distributors considering how the two technologies fit together when a home is extended and its heating design is reviewed.
*Wet underfloor heating pipework installed over foil-faced insulation in the UK home extension.*
Project snapshot
- **Location:** United Kingdom
- **Property:** house with a single-storey rear extension
- **System:** wet underfloor heating served by an R290 air-to-water monobloc heat pump
- **Emitter:** underfloor heating across the ground-floor rooms and hallway
- **Manifold:** stainless-steel manifold with seven visible circuits, labelled per room
- **Heat source:** R290 air-to-water monobloc heat pump
- **Floor build-up:** foil-faced rigid insulation, perimeter edge strip and pump-delivered screed
- **Status:** installed, March/2025
Why underfloor heating suits a heat pump
Underfloor heating and heat pumps tend to work well together because they want the same thing: a low water temperature. A large floor area acts as the emitter, so the system can deliver comfort while running much cooler flow temperatures than a traditional radiator circuit. Heat pumps are, in turn, at their most efficient when they are asked to produce lower-temperature water — the smaller the lift between outdoor air and flow temperature, the better the performance tends to be.
For an extension specifically, underfloor heating can offer a few practical advantages:
- **Open-plan comfort.** Radiant heat from the floor can suit large, open living spaces where sizing wall radiators is awkward.
- **Freed wall space.** No radiators means fewer constraints on furniture, glazing and layout.
- **A natural low-temperature pairing.** The emitter is designed around low flow temperatures, which is the operating point a heat pump prefers.
These are general characteristics of the papring rather than guarantees for any one property — actual comfort and running cost depend on insulation levels, floor construction, controls and how the system is commissioned.
Step 1 — Subfloor preparation and insulation
The build-up starts with rigid insulation laid over the prepared subfloor. Insulation below the pipe matters because it helps direct the heat upward into the room rather than downward into the ground or structure, which supports both comfort and efficiency. A perimeter edge strip is run around the walls to accommodate thermal movement of the screed and to reduce heat loss at the edges.
The available photographs begin after the pipework has been installed, so the insulation type and thickness should be confirmed from the project record before publication.
Step 2 — Pipe layout
With the insulation down, the heating pipe is clipped out across the floor. Spiral layouts are visible in the larger rooms, while the narrower circulation areas use layouts adapted to the available space. A spiral can place outward and returning pipe runs alongside one another, helping distribute surface temperature more evenly when the circuit is designed that way.
Pipe spacing is generally set tighter in areas with higher heat loss — for example near large glazed openings or external walls — and wider elsewhere.
*Separate floor-heating circuits routed through the hallway and around the staircase.*
Step 3 — Manifold, circulation and balancing
Each underfloor circuit returns to a central manifold, where the system is distributed and balanced. Seven circuits are visible on this installation, with handwritten room labels including bathroom, kitchen, living areas and corridor. Clear labelling supports commissioning and future servicing.
Visible on the manifold assembly:
- **Per-circuit flow meters**, used to balance flow between circuits so each zone receives its designed share.
- A **circulation pump** (Grundfos UPM3) driving the underfloor circuit.
- A **blending / mixing valve** arrangement, which sets the temperature of the water sent to the floor.
- **System gauges** for commissioning and monitoring.
It is standard practice to pressure-test the pipework and keep it under pressure through the screed pour, so that any damage shows up immediately rather than after the floor is buried.
A thermostatic mixing and circulation assembly appears to be fitted. The exact control strategy — including whether the R290 heat pump runs weather-compensated and how the floor flow temperature is regulated — should be confirmed from the commissioning record before it is described in detail.
*Seven-circuit stainless-steel manifold with flow meters, room labels and a circulation assembly.*
Step 4 — Screed pour and curing
Once the circuits are tested, pump-delivered screed is placed over the pipework, distributed manually and levelled across the floor. Full encapsulation matters because the screed transfers and spreads heat from the pipework; voids around the pipe can reduce heat transfer. The photographs appear consistent with a semi-dry screed installation, but the exact material and thickness should be confirmed with the installer.
After installation, the screed needs to cure before heat is applied. Drying time depends on the material, thickness and site conditions, so the screed supplier's and underfloor-heating manufacturer's guidance should be followed rather than assuming a fixed period.
Commissioning normally follows the documented curing period and a controlled first heat-up procedure. The correct schedule should come from the screed supplier, underfloor-heating manufacturer and project commissioning plan.
*Pump-delivered screed being placed over the floor-heating pipework.*
*The screed is distributed and levelled manually across the floor.*
Step 5 — Finished floor
The photographs show a smooth, newly finished screed surface. After the specified curing and drying period, it can receive a compatible final floor finish such as tile, engineered wood, LVT or carpet. The pipework is permanently encapsulated and normally requires no routine access, while the manifold, controls and heat source remain accessible for inspection and servicing.
*Levelled screed across the extension after the underfloor-heating pipes were covered.*
*Newly finished screed covering the underfloor-heating circuits.*
*The completed screed surface continues through the hallway.*
The heat source — an R290 air-to-water monobloc heat pump
Heat for the underfloor system is provided by an outdoor **R290 air-to-water monobloc heat pump** carrying the MEGAWAVE customer brand. The project source confirms R290 refrigerant; the precise model and rated heating output remain to be confirmed. In a monobloc arrangement, the sealed refrigerant circuit is contained in the outdoor unit and insulated water connections run into the property.
R290 is propane and is classified as a flammable refrigerant, so siting, clearances and service access must follow the model-specific installation manual and applicable local requirements. The photograph documents the installation but, by itself, does not verify compliance distances or commissioning settings. For more background, see Nordtherm's guide to [R290 heat pump safety](https://nordthermglobal.com/blog/r290-heat-pump-safety-what-distributors-need-to-know-before-importing).
What makes this type of heat pump a natural fit for underfloor heating is less about headline specifications and more about how it likes to run:
- **Low flow temperatures.** The floor is a large emitter, so it can heat the room with cooler water than radiators need — and a heat pump is generally at its most efficient when producing lower-temperature water.
- **Weather compensation.** The unit can vary flow temperature with outdoor conditions, nudging it only as high as the day actually requires, which tends to help seasonal efficiency.
- **A sealed monobloc refrigerant circuit.** With the R290 circuit contained in the outdoor unit, the external connections visible here are insulated water pipes and electrical/control services.
Together these traits allow the heat pump and underfloor circuit to be designed as one low-temperature system. Explore Nordtherm's [R290 residential air-to-water heat pump range](https://nordthermglobal.com/products/r290-air-to-water-split-heat-pump-for-heating-cooling-and-hot-water) for available OEM configurations; the linked range should not be read as confirmation of the exact model used in this project.
*Outdoor R290 air-to-water monobloc heat pump with insulated water connections routed into the property.*
What a low-temperature heating system means here
"Low-temperature heating" simply means the system is designed to warm the home using cooler water than a traditional radiator setup. Where an older system might circulate hot water, an underfloor system spreads heat over a large surface, so it can keep a room comfortable at a much lower flow temperature.
That lower operating point is the thread linking every stage of this project. It is why the floor is insulated (to push heat upward efficiently), why the pipe is spaced to give an even output, and why a heat pump is a sensible heat source — the cooler the water it has to produce, the more it works in its favour. The trade-off is that a low-temperature system has to be designed as a whole: emitter, controls and heat source are all sized around that lower temperature. Done well, the result is steady, even warmth rather than the blast-and-cool cycle of a hot radiator.
Why this approach works for UK extensions
This project is a fairly typical example of how a modern UK extension can be heated: a low-temperature, radiant underfloor system, balanced across labelled zones at a central manifold, and driven by an air-to-water heat pump running the low flow temperatures it prefers. The combination suits open-plan layouts, frees up wall space, and forms a low-temperature heating system that can be well matched to renovation and extension work.
As with any heating design, results depend on the property — insulation, floor construction, controls and commissioning all play a part — so the specifics here should be read as one worked example rather than a fixed specification.
Common questions
**Why is insulation installed under underfloor heating?**
Insulation below the pipe helps direct heat upward into the room rather than downward into the ground or structure. Without it, a share of the output would be lost beneath the floor, which can affect both comfort and running cost.
**Why are spiral pipe layouts used?**
In a spiral (counter-flow) layout, flow and return pipes run alongside each other, so warmer and cooler pipe alternate across the floor. This tends to even out the surface temperature and avoid a noticeably hotter zone where the water enters. Serpentine layouts are often used in narrow spaces where a spiral will not fit.
**Why is screed poured over the pipes?**
The screed encapsulates the pipe and acts as a thermal mass that stores heat and spreads it evenly across the floor. Full encapsulation matters, as voids around the pipe would create uneven output. The screed then needs to cure before heat is applied, with a gradual first heat-up to reduce the risk of cracking.
**Can underfloor heating work with wooden floors?**
It can, but the floor finish matters. A covering with high thermal resistance slows heat transfer, so engineered wood — which is more dimensionally stable than solid timber — is generally preferred, and the flooring manufacturer's maximum floor-surface-temperature guidance should be followed. Tile and stone conduct heat most readily; carpet and thick underlay resist it most.
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Continue exploring
- 🏠 [**R290 residential air-to-water heat pumps**](https://nordthermglobal.com/products/r290-air-to-water-split-heat-pump-for-heating-cooling-and-hot-water) — product options for heating, cooling and domestic hot water projects.
- 🛡️ [**How heat pump warranty works**](https://nordthermglobal.com/blog/how-heat-pump-warranty-works-what-distributors-need-to-know-before-buying) — coverage, exclusions, claims and after-sales questions distributors should check.
- 🔥 [**R290 heat pump safety for distributors**](https://nordthermglobal.com/blog/r290-heat-pump-safety-what-distributors-need-to-know-before-importing) — monobloc design, documentation and installation considerations.
- 🔧 [**Inside an R290 air-to-water heat pump**](https://nordthermglobal.com/blog/inside-an-r290-air-to-water-heat-pump-a-look-at-what-really-matters) — internal construction and serviceability.
- 📖 [**Can underfloor heating be installed in an existing house?**](https://nordthermglobal.com/blog/can-underfloor-heating-be-installed-in-an-existing-house-a-retrofit-guide) — a companion guide covering retrofit options and planning constraints.
- 📸 [**Related UK project: underfloor heating with fan-coil cooling**](https://nordthermglobal.com/case/air-to-water-heat-pump-retrofit-for-an-existing-uk-house-with-underfloor-heating-and-fan-coil-cooling) — a different retrofit approach using low-profile panels.
**Planning a similar underfloor heating project?**
Tell us about your property or project — target market, floor area, design flow temperature and required functions — and we can help you select a suitable R290 air-to-water heat pump configuration. Nordtherm supports residential heat-pump projects and OEM programmes for the UK and European markets.
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