From intent to in-use: The role of emitters in heat pump efficiency
From intent to in-use: The role of emitters in heat pump efficiency
The UK may be accelerating toward low-carbon heating, but true performance depends on more than the heat pump itself. Here, Shane Cox, Managing Director at Itherme, explains why correctly designed heat emitters are the fundamental for comfort, efficiency and long-term system performance.
With a 63% increase in domestic heat pump installations in 2024, the UK’s shift to low-carbon heating is well underway. And, with the incoming Warm Homes Plan and Future Homes Standard – alongside the expansion of the BUS Scheme and changes to Permitted Development Rights – this growth is only set to continue across an even broader range of buildings.
Yet, one critical element is still frequently overlooked: heat emitters. Regardless of how efficient a heat pump may be, undersized or poorly configured emitters could undermine overall system performance.
Too many installations still treat legacy boiler circuits as though they are compatible with low-temperature heat pumps. However, traditional radiator systems are designed for 70-80°C operation, meaning they often lose more than half their heat output once flow temperatures drop into the mid-40s. Raising the flow temperature of a heat pump system simply masks the problem, instead, driving inefficiencies, increasing running costs and causing excessive heat pump cycling.
Why standard solutions fall short
Put simply, whether a heat pump can provide comfort depends on how well heat is delivered into a space. For example, when underfloor heating (UFH) is designed using accurate calculations of the building’s thermal loads, it provides consistent warmth even at lower flow temperatures. This is because its large surface area and steady heat output align naturally with the operating characteristics of heat pumps, making it an ideal solution when specified from the outset.
Where this becomes more complex is in retrofit projects. The UK has some of the oldest housing stock in Europe, so specifiers are increasingly working across a wide variety of building types, each with different performance demands. As a result, the correct approach is not simply to reuse existing radiators or substitute emitters on a like-for-like basis, but to carry out detailed building diagnostics before specifying a system.
That means assessing room-by-room heat losses, insulation levels and cold bridges, modelling flow temperatures, and validating whether existing emitters can meet peak load under low-temperature operation.
This diagnostic stage often reveals that original radiators are undersized for heat pump conditions. When those insights are ignored, the outcome is predictable: slow warm-up times, persistent cold spots, and heat pumps forced to cycle excessively to overcompensate.
By contrast, when emitters are sized to meet the bespoke needs of a property using thermal analysis, a system’s behaviour can improve dramatically. Homes that once struggled to reach a comfortable temperature can become balanced, with rooms that heat evenly, and a system that settles into steady, efficient operation rather than a stop-start pattern.
This approach underpins Itherme’s UFH solutions. Manufactured using high-quality components exclusively from the UK and Europe, its engineered screeded, joisted and low-build up retrofit systems are designed to deliver reliable, even heat distribution at the low flow temperatures that heat pumps rely on. And selecting the right emitters for each application is critical, as the comfort a heat pump provides is shaped less by the maximum water temperature and more by how evenly and reliably heat is supplied throughout the home.
When emitters are correctly specified and manufactured using reliable components, steady performance comes naturally. When they are not, it’s almost inevitable that some rooms never meet maximum comfort – and the heat pump will be blamed for shortcomings that have nothing to do with the technology itself.
The sound of efficiency
Poor system design doesn’t just impact thermal comfort, either. Noise-related complaints are often an early indicator that system performance is being compromised. When the emitters aren’t dissipating heat efficiently, the heat pump works harder: flow rates increase, the pump ramps up, and the system begins to cycle aggressively. That can translate into increased fan activity and noisy operation, even though, mechanically, nothing is “broken”.
We recently assessed a heritage property where the heat pump installation was technically excellent but rendered unpopular due to the noise. After recalculating the emitter surfaces and optimising flow, sound levels dropped significantly while energy performance improved in parallel. Situations like this make it clear that the “loud heat pump” is rarely a product fault; it is a symptom of a system that was never properly engineered for low-temperature operation.
Itherme’s systems are designed with acoustic sensitivity in mind. For example, our Gypsumdek 18 retrofit system can be installed seamlessly on top of a vast range of acoustic products without the need for mechanical fixings. This maintains the performance of the acoustic product below the system, enabling quiet operation, even in multi-storey buildings.
Getting it right, first time
The importance of getting emitter decisions right mirrors challenges we see elsewhere in construction: when material choices are poor or considered too late, waste, inefficiencies, rework, and poor performance become the default.
Heat pumps are just one example of this. If emitters are not designed for low-temperature operation from the outset, the entire system becomes compromised. And, once those shortcomings are locked in, inefficiencies can be more difficult to reverse.
With over 15 years’ experience, at Itherme, we set out to prevent this from happening. Our technical support and European manufactured heating systems combine robust design, quality components and expertise, ensuring high-performing solutions, whatever the project’s requirements.
Because considering emitters early is fundamental if heat pumps are to perform successfully at scale. Without this, the gap between design intent and real-world performance widens, undermining confidence in the technology and risking the industry’s progress.
However, if we get the foundations right, mass heat pump adoption can succeed based on performance, not just policy.
ITHERME is a leading designer and manufacturer of high-performance underfloor heating systems, specialising in bespoke solutions for the construction industry. With over 15 years of experience, ITHERME provides energy-efficient, sustainable heating systems tailored to suit a wide range of floor types, including screeded, joisted, low build-up retrofit, and electric underfloor heating. Its products are manufactured exclusively in the UK and Europe, combining rigorously tested components with industry-leading smart control technology.
Serving architects, M&E contractors, specifiers, developers, and professional installers, ITHERME is known for delivering innovative, energy efficient heating solutions that meet modern building regulations and sustainability standards. The company offers expert design advice, straightforward installation guidance, and ongoing support to ensure customer satisfaction.
Trusted on high-end residential and commercial projects throughout the UK, ITHERME helps clients achieve optimal comfort, energy savings, and future-proof performance. For tailored underfloor heating solutions and exceptional service, ITHERME is the trusted partner for progressive construction projects.
