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early in the design process. Late changes to floor finishes can have a significant impact on system performance.


Retrofit applications The use of UFH in retrofit applications has increased since 2021, supported by the development of low-profile systems. Retrofit installations present


several challenges, including floor height constraints, existing building fabric performance and limitations on achievable heat output. In many cases, it may not be possible to achieve sufficient output from UFH alone. It is also important to recognise that


UFH is not always the most appropriate solution in retrofit scenarios. In buildings with higher heat losses, improving the building fabric may be a more effective first step before considering UFH installation. Where UFH is used in retrofit, a mixed-


emitter approach may be appropriate, combining UFH with radiators or other emitters to meet peak demand.


Installation and commissioning The successful delivery of UFH systems requires a structured approach to design and installation, but in practice it is often the quality of installation and commissioning that determines whether a system performs as intended. During installation, adherence to the


design layout is critical. Pipe spacing, circuit lengths and zoning arrangements are carefully determined during the design stage to achieve required outputs. Deviations on site, such as widening pipe spacing to save time or adjusting layouts to suit other trades, can lead to uneven heat distribution and reduced performance. Protection of pipework during


installation is also essential. It is not uncommon on site for pipework to be exposed to damage from foot traffic, tools or other trades prior to screeding. Even minor damage can result in leaks that are extremely disruptive and costly to rectify once the floor is complete. For this reason, pressure testing is often carried out prior to screeding and maintained during the pour to identify any issues immediately. Insulation installation is another


area where performance can be compromised. Gaps in insulation or poorly fitted perimeter insulation can lead to heat losses that are not immediately apparent but result in higher running costs and reduced comfort. These issues are often only identified


Case Study – Rosslyn Castle, Edinburgh.


In 2022 Rosslyn Castle, a 14th-century castle, was refurbished using underfloor heating. A central challenge of the £4 million restoration was delivering efficient, low-temperature heat distribution compatible with the newly installed air source heat pumps (ASHPs), while preserving the building’s historic fabric. REHAU’s UFH system was specified to operate at low flow temperatures,


maximising the coefficient of performance (COP) of the ASHPs. This approach ensured consistent, radiant heat across large volumes such as the castle’s great hall—spaces traditionally difficult to heat using conventional radiators. Installation required a tailored, room-by-room strategy. In areas


with suspended timber floors, original oak boards were carefully lifted, catalogued, and reinstated following the installation of aluminium diffusion plates and pipework. These plates enhance heat transfer and ensure an even surface temperature while maintaining minimal floor build-up, critical in preserving existing floor levels. In the great hall, a screed rail system was deployed over an eco-friendly


recycled glass fibre (Geocell) insulation base. This provided both structural support and thermal efficiency, with a mesh grid securing the pipework within the screed layer. The system design balanced heritage constraints with modern


performance standards, demonstrating how UFH can deliver discreet, energy-efficient heating without compromising historic integrity.


Acknowledgments With thanks to Steve Richmond, sales and marketing director at REHAU, for his contribution and technical insight.


once the system is operational, at which point remediation is problematic. Commissioning is frequently the


most overlooked stage of the process, yet it has a direct impact on system performance. Systems should be thoroughly flushed to remove debris introduced during installation. Failure to do so can result in blockages or reduced flow rates within circuits.


Air removal is equally important.


Trapped air within the system can prevent proper circulation and lead to cold spots within the floor. In larger systems, this can be difficult to identify without careful commissioning. Flow balancing across circuits is


essential to ensure that all areas receive the correct proportion of heat. Without balancing, some rooms may overheat


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while others remain underheated, leading to user dissatisfaction and inefficient operation. Finally, control systems should be set


up and tested in accordance with the design intent. This includes verifying that thermostats, actuators and control valves are operating correctly and that zoning strategies are functioning as expected. In practice, many reported issues with


UFH systems can be traced back not to design limitations, but to shortcomings in installation and commissioning.


Emerging trends Several trends are shaping the future of UFH systems, reflecting broader changes in building design and energy use. One of the most significant


developments is the increasing role of smart controls. Modern systems are no longer limited to basic thermostatic control but can incorporate app-based interfaces, remote monitoring and adaptive learning. These systems can adjust operation based on occupancy patterns, external temperatures and user behaviour, helping to optimise performance. This increased sophistication,


however, also introduces complexity. Poorly configured smart controls can lead to unintended outcomes, such as excessive cycling or conflicting zone demands. As a result, there is a growing need for clear commissioning procedures and user guidance to ensure that systems are used effectively. Another key trend is the growth


of retrofit applications. As existing buildings are upgraded to meet future energy standards, UFH is being considered more frequently as part of refurbishment projects. This has driven the development of low-profile systems and modular solutions designed to minimise disruption. In practice, retrofit projects often


highlight the limitations of UFH as well as its advantages. Systems must be carefully matched to the building, and in some cases a combination of emitters can provide a more effective solution than UFH alone. There is also a growing emphasis


on system integration. UFH is increasingly considered as part of a wider building energy system that may include heat pumps, thermal storage, solar generation and smart energy management. This integrated approach allows for better optimisation of energy use across the building.


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