The transition to cleaner home heating is one of the biggest climate challenges facing the UK. With millions of homes built before the 1980s, many homeowners remain deeply sceptical: can a modern heat pump truly work efficiently without costly, disruptive insulation upgrades to 'new build' standards?
Fresh research from Germany’s renowned Fraunhofer Institute for Solar Energy Systems (ISE) provides a powerful and timely answer: Yes, they can.
The findings from the major research project, titled "Quality Assurance of Heat Pumps in Existing Buildings" (WP-QS in Existing Buildings), directly challenge the assumption that heat pumps are only suited to modern or fully retrofitted homes. This is a crucial piece of news for UK policy-makers and millions of households considering moving away from natural gas boilers.
Efficiency Confirmed: Age is Just a Number
The Fraunhofer ISE study monitored 77 heat pump systems in existing homes, some dating back to the 19th century, under real-world conditions. The results offer compelling evidence of their performance:
- Air/Water Heat Pumps achieved an impressive average Seasonal Performance Factor (SPF) of 3.4. This means that for every one unit of electricity used, the system generated 3.4 units of heat.
- The more efficient Ground-Coupled Systems performed even better, reaching an average SPF of 4.3.
Crucially, the research found no correlation between the year of a building’s construction and the heat pump’s efficiency. This dispels the myth that only highly insulated homes can achieve good performance. The study also noted that adequately sized radiators, common in older UK homes, were able to operate at the necessary low temperatures, much like underfloor heating.
A Decisive Reduction in Carbon Emissions
The environmental impact is equally significant. When comparing the heat pumps to traditional natural gas heating systems, the reduction in greenhouse gas emissions is profound.
By taking into account the German electricity mix from 2024, the study calculated that the heat pumps delivered CO2 emission reductions of 64% on average compared to gas boilers. This calculation even used a dynamic accounting method - factoring in quarterly variations in the grid's carbon intensity—to provide a more precise, conservative figure. This significant cut demonstrates the technology’s critical role in meeting national decarbonisation goals.
The Path to Optimal Performance
While the efficiency results were overwhelmingly positive, the Fraunhofer team did identify a key area for optimisation that is highly relevant to the UK installation industry.
The analysis revealed that a significant number of heat pumps were oversized relative to the building’s consumption needs, which led to excessive cycling and reduced efficiency. This suggests that better initial sizing and system design are essential to maximise a heat pump’s performance and service life.
The researchers also conducted long-term sound measurements on air/water units. While some noise exceedances were measured at night, the report confirms that these remained below the overall ambient noise levels. They also stated that compliance with German noise regulations could have been achieved with simple steps, such as:
- Selecting quieter models.
- Optimising the placement of the outdoor unit.
- Implementing standard soundproofing measures.
Finally, the study highlighted the excellent synergy between heat pumps and photovoltaic (PV) systems. Pairing the two significantly boosted energy self-consumption and building autonomy, particularly when a home battery was added, demonstrating a pathway to almost complete energy independence.
Summary and Call to Action
The research from Fraunhofer ISE provides powerful evidence that heat pump technology is mature, highly efficient, and a viable climate-friendly heating solution for the UK’s existing housing stock. The core message is clear: achieving climate-friendly heating does not have to mean gutting an older home. With sound design, the benefits are immediately accessible.
The focus must now shift from questioning the technology’s suitability to ensuring high-quality installation and appropriate system sizing across the UK.