Dr Marek Miara is one of Europe’s leading experts in heat pumps. A senior scientist and coordinator at the Fraunhofer ISE for over twenty years, he leads extensive monitoring projects to evaluate heat pump performance in real-world conditions. His crucial contribution has been debunking the myth that heat pumps are only effective in highly insulated new builds: his research has shown they achieve high efficiency even in older, existing buildings with traditional radiators and in multi-family complexes.

Strategic adviser for organisations like the European Heat Pump Association (EHPA), Miara is currently a key figure in the urban heat transition, promoting heat pumps to replace gas boilers without requiring a complete overhaul of city infrastructure.

BUILD UP (BUP):  Could you provide a high-level overview of the current landscape for heating and cooling in Europe’s new-build construction sector, outlining how dominant heat pumps have become and which technologies continue to be used as primary alternatives or as backup solutions?

MAREK MIARA (MM): Europe’s heating landscape is highly diverse. Heat pumps have made significant inroads in new residential construction across many markets, yet the overall picture remains highly diverse — both in terms of market penetration and technology mix. This contrast is striking: Norway has over 600 installed heat pumps per 1,000 households, while Germany sits at around 50. Even within a single year, markets moved in opposite directions — 2024 saw an overall contraction of around 22%, driven by policy uncertainty, subsidy changes, and an unfavourable electricity-to-gas price ratio in many countries, while the recovery in 2025 is encouraging but uneven.

The technological diversity mirrors this geographic variety. In countries with hydronic heating systems — predominant across Central and Western Europe — air-to-water heat pumps dominate. In Scandinavia and Southern Europe alike, air-to-air systems are widespread, serving not only heating but also cooling needs, which is an increasingly important consideration as summers become hotter.

Alternative technologies vary equally by country. In traditionally gas-heavy markets, gas boilers still dominate the existing stock. Biomass heating is significant in several Central and Eastern European countries. District heating plays a major role in many Northern and Eastern markets. Hybrid heat pumps have found particular traction in the Netherlands, and in some countries, such as Poland, coal boilers remain a significant part of the picture.

What unites this diversity is a shared direction: across virtually all European countries, heat pumps are recognised in national decarbonisation strategies as the primary long-term solution for building heating. The paths differ, but the destination does not.

BUP:  In considering the decarbonisation of Europe’s existing building stock — much of which still depends on high-temperature radiator systems — what are the principal technical and structural challenges associated with integrating heat pumps into these older properties?

MM: Field monitoring projects conducted across Europe over the past 20 years — including long-running studies at Fraunhofer ISE that I led for many years — have consistently shown that heat pumps perform well in existing buildings, including those with traditional radiator systems. Across more than 840 monitored installations from studies in Germany, France, Switzerland, the UK, Austria and the Netherlands, heat pumps in existing buildings — including older, poorly insulated ones — delivered heating efficiently and reliably. What these studies repeatedly confirmed is that a building’s age alone is not the determining factor. The quality of system design, hydraulic balancing, and commissioning makes the real difference.

That said, efficiency is always better when buildings are well-insulated and operate at lower flow temperatures, and renovation and heat pump deployment should go hand in hand wherever possible. But renovation is not a prerequisite for installing a heat pump, and framing it as one has unnecessarily blocked too many transitions.

Modern heat pumps have also shifted the technical baseline considerably. Delivering flow temperatures of up to 70–75°C is increasingly standard across the product range, and in many retrofit situations, small, targeted measures — replacing the radiator in one or two particularly cold rooms, improving hydraulic balancing — are sufficient to enable efficient operation without a full-scale renovation.

To be clear: there are real challenges with heat pumps in existing buildings, but they are not where many people claim. Technical feasibility is well established by evidence. The challenges that do exist — system integration, correct sizing, hydraulic design — are in most cases solvable, and that is where the focus should be.

‘There are real challenges with heat pumps in existing buildings, but they are not where many people claim’

BUP: Domestic Hot Water (DHW) remains one of the biggest challenges for heat pumps in existing multi-family buildings. Anti-legionella regulations require maintaining high water temperatures (above 60°C), which inherently penalises the heat pump's efficiency (COP). What are the most effective configurations you propose for DHW production to maintain high system efficiency?

MM: Multi-family buildings are fundamentally more diverse than single-family homes — in size, ownership structure, system age, and how heating and hot water are organised. This variability is, on the one hand, a challenge because standardised solutions are harder to establish. On the other hand, it is also an opportunity, because different configurations and approaches can be applied depending on what a specific building actually needs.

Domestic hot water is where this complexity is most visible. Hygiene regulations across Europe require high storage and distribution temperatures to prevent Legionella growth — in many countries, at least 60°C — which requires careful system design to maintain good heat pump performance.

Several approaches exist to address this. Decentralised systems — where each apartment has its own small heat pump water heater — avoid long circulation loops and high heat losses, though they require space and higher investment per unit. In central systems, modern heat pumps using refrigerants like R290 can reach 70–75°C and handle thermal disinfection directly. A third path, still under active research, combines ultrafiltration with lower storage temperatures below 50°C, removing the need for high-temperature operation while maintaining hygienic safety.

The optimal solution depends on building size, system age, and the scope of renovation. DHW in multi-family buildings is a genuine challenge — but in most cases, a solvable one, provided it receives the attention it deserves early in the planning process.

BUP: Regarding high-temperature heat pumps: moving beyond the industrial sector, do you see these as a game-changing solution for the residential building stock? Are they the 'silver bullet' for older buildings where conventional, lower-temperature heat pumps might struggle to perform?

MM: The term ‘high-temperature heat pump’ can be confusing, and it is worth clarifying what it actually means. In industrial applications, high temperature typically refers to systems delivering above 100°C. In the residential sector, heat pumps producing above 55°C were considered high-temperature for many years — but that is increasingly the standard today. Modern heat pumps routinely reach above 70°C, and some models go up to 80°C.

It is also important to understand when these temperatures are actually needed. In most buildings, the design flow temperature — the maximum the system was planned for — is only required on the coldest days of the year. For the majority of the heating season, heat pumps operate at significantly lower temperatures, which is where their efficiency is at its best.

For me, the availability of these modern high-temperature models removes one of the most common concerns about heat pumps in existing buildings: the worry that the system simply will not keep the house warm. That concern is understandable, but largely unfounded with today’s technology.

At the same time, the question worth asking is always: can we avoid the need for those peak temperatures in the first place? In many cases, existing radiators are already oversized for the actual heat load, meaning the design temperature is not genuinely necessary. And where there are critical rooms that do require higher temperatures, replacing just those radiators is often a straightforward and low-cost measure. A careful system assessment before installation can make the difference between a heat pump that occasionally struggles and one that performs well throughout the year.

‘The availability of these modern high-temperature models removes one of the most common concerns about heat pumps in existing buildings: the worry that the system simply will not keep the house warm’

BUP: In the installation, commissioning and maintenance of innovative heat pumps, do you recognise a skills gap that prevents a full uptake in the implementation of heat pump technologies? Are there new skills that need to be acquired?

MM: Yes, the skills gap is real, and it is one of the most significant bottlenecks to scaling heat pump deployment across Europe. The European Heat Pump Association (EHPA) estimates that over 500,000 heat pump professionals will be needed by 2030 to meet EU climate targets — a number that current training pipelines are far from reaching. But the challenge is not just quantitative. Having spent years coordinating international research projects on heat pump performance in buildings, I have seen repeatedly that poor installation and commissioning quality is one of the leading causes of underperforming systems — and of consumer dissatisfaction. A heat pump installed incorrectly can appear to ‘not work’, even when the technology is perfectly sound. This does enormous damage to public perception.

The skills required go well beyond knowing how to install a heat pump. They include system design in complex existing buildings, hydraulic balancing, commissioning and verification protocols, and increasingly, digital monitoring and remote diagnostics. And looking ahead, the demands will only grow. As heat pumps are integrated with photovoltaic systems, battery storage, and smart home controls, installers are no longer simply laying pipes — they are becoming key actors in the energy transition, responsible for complex, interconnected energy systems. This requires continuous training, new qualifications, and new areas of expertise. It may even call for new professional profiles altogether. Investing in this workforce — and making it an attractive career path for the next generation — must be treated as a policy priority alongside subsidy schemes.

BUP: To conclude, what key recommendations would you offer to heating, ventilation, and air conditioning (HVAC) designers and real estate stakeholders who are currently navigating the transition to heat pumps within existing property portfolios?

MM: My primary recommendation is simply this: be brave and take the step. There is plenty of evidence showing that heat pumps work in existing buildings — including complex multi-family ones. Sometimes the challenges are greater than in straightforward cases, but in almost every situation, a solution can be found.

Beyond that, the most important shift is from a component-replacement mindset to a systems perspective. A heat pump is not a boiler — it is part of an integrated system that includes the distribution network, storage, controls, and the building envelope. Good decisions in the design phase, particularly around flow temperatures and hydraulic layout, will determine whether the system performs well for the next 20 years.

For HVAC designers: invest in a thorough assessment before sizing equipment. Actual heat demand and real operating temperatures often differ substantially from design assumptions, and that analysis pays off. For real estate stakeholders: heat pump retrofits work best when planned as part of a broader renovation strategy rather than as isolated measures, and early engagement with tenants or co-owners reduces project risk considerably.

One last point: do not start from scratch. There is a growing body of field experience and international research that documents what works and what does not, across very different building types, climates, and ownership structures. That knowledge is there — and using it makes every project better.