PHAM NEWS | MARCH 2026 18 HeatPumps


Only as good as the heat emitters


The UK may be accelerating toward low-carbon heating, but effi cient system performance depends on more than the heat pump alone, says Shane Cox from Itherme.


T


he UK’s shift to low-carbon heating has gained momentum, which is refl ected in a 63%


increase in domestic heat pump installations in 2024. 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 effi cient a heat pump may be, undersized or poorly confi gured 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 fl ow temperatures drop into the mid-40s. Raising the fl ow temperature of a heat pump system simply masks the problem, instead, driving ineffi ciencies, increasing running costs and causing excessive heat pump cycling.


Bespoke approach Put simply, whether a heat pump can provide comfort depends on how well heat is delivered into a space. For example, when underfl oor heating (UFH) is designed using accurate calculations of the building’s thermal loads, it provides consistent warmth even at lower fl ow 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 specifi ed from the outset. Where this becomes more


complex is in retrofi t projects. The UK has some of the oldest


Shane Cox MD of Itherme


 Heat pump selection is only half the battle – system effi ciency and comfort also depend on the choice of emitter


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 fl ow, sound levels dropped signifi cantly 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 improperly engineered and, therefore, destined to fail. Itherme’s systems are


housing stock in Europe, so installers and specifi ers are working with a wide variety of buildings, each with diff erent needs. 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 NUMBERS 63%


the increase in domestic heat pump installs in 2024


>50%


radiator heat output can fall by over 50% at heat pump fl ow temperatures


70-80°C


conventional systems typically designed within this fl ow temperature range


~45°C 15


Itherme has over 15 years of experience in UFH


heat pump systems typically designed to this fl ow temperature


by-room heat losses, insulation levels and cold bridges, modelling fl ow temperatures, and validating whether the existing emitters can meet peak load at 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, effi cient operation rather than a stop-start pattern.


Underfl oor heating This is the principle behind Itherme’s UFH solutions: manufactured using high- quality components exclusively from the UK and Europe, its engineered screeded, joisted and lowbuild-up retrofi t systems are designed to deliver reliable, even heat distribution at the low fl ow


Regardless of how efficient a heat pump may be, undersized or poorly configured emitters could undermine overall system


performance


temperatures that heat pumps rely on. And selecting the right emitters for the circumstance is critical as the comfort a heat pump provides is shaped less by maximum water temperature, and more by how evenly and reliably heat is supplied throughout the home. When emitters are correctly


specifi ed 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.


Quiet performance Poor system design doesn’t just impact thermal comfort, either. Noise-related complaints are a key indicator that the system is not operating as intended. When the emitters aren’t dissipating heat effi ciently, the heat pump works harder: fl ow rates increase, the pump ramps up, and the system begins to cycle aggressively. That can translate


designed with acoustic sensitivity in mind. For example, our Gypsumdek 18 retrofi t system can be installed seamlessly on top of a vast range of acoustic products without the need for mechanical fi xings. This maintains the performance of the acoustic product below the system, enabling quiet operation, even in multi-storey buildings.


First time right The importance of getting emitter decisions right mirrors challenges we see elsewhere in construction: when material choices are poor or considered too late, waste, ineffi ciencies, 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, ineffi ciencies can be more diffi cult 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. 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 confi dence in the technology and risking the industry’s progress. However, if we get the foundations right, the heat pump boom can be both rapid and reliable. ◼ phamnews.co.uk/326/31


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