Rebecca Hogg, Technical Manager at BSRIA, examines how the rapid growth in heat pump installations is challenging designers to adopt a more holistic approach to system design.

2024 was a record-breaking year for the heat pump market. It saw nearly 110,000 units sold, which represents an increase of 48% on the previous year, making it the strongest year on record. Half of the units sold went to the replacement sector, and the rate of retrofit applications is continually increasing.

While this surge in demand highlights a significant moment in the energy transition, it also places pressure on national electrical infrastructure. This increases the responsibility of system designers to ensure that the systems specified will deliver on the design intention and mitigate any risk of a performance gap developing, where energy demand exceeds design capacity and consequently running costs are higher than forecast. 

The challenge is that, when it comes to low-energy systems, there is no one-size-fits-all solution. 

A growing trend

There are numerous factors behind the ongoing heat pump acceleration. Notably, the easing of planning restrictions through Permitted Development Rights (PDR) which were updated earlier this year. 

The changes include an increased maximum unit size – more than double the previous 0.6 cubic meters to 1.5 cubic meters – to allow a range of designs and potential inclusion of sound insulation materials or different fan types. In addition, the one-meter boundary restriction was also lifted, which removed the need for planning permission for heat pump installations on houses that are close to neighbouring properties, such as terraced houses. This had previously been a significant barrier to uptake, particularly when considering that terraced properties make up around 24-31% of the housing stock in England and Wales.

These regulatory updates expand the range of applications for heat pumps, facilitating a more seamless integration into a wider range of both new and existing housing stock.

Alongside regulatory change, consumer awareness has been propelled by mainstream media and campaigning from the industry, in particular major energy providers. This has resulted in heat pumps increasingly being seen as both environmentally responsible and economically beneficial alternatives to fossil fuel heating, particularly in retrofit projects where incentives like the Boiler Upgrade Scheme offer grants of up to £7,500.

A holistic approach

The versatility of heat pump applications provides greater scope for use across a range of low carbon solutions whether this be space heating, cooling or domestic hot water production. However, while the increasing momentum behind heat pump adoption signals progress in the wider drive for decarbonisation, challenges exist for designers.  

For those specifying or designing heat pumps systems, accurately quantifying a building’s baseline performance is essential to ensure correct system sizing and achieving optimal system performance. The outputs from rapid building performance measurement techniques will also influence the sizing of the heat sink whether this be an underfloor heating system or panel radiators. 

But the challenges don’t end there. While the requirements of the heat pump itself must lay the foundation of a design, to ensure that the system will perform effectively, designers need a holistic understanding of the building’s fabric and energy profile. 

Historically, the industry has relied on Energy Performance Certificates (EPCs) to assess performance needs and guide system sizing. However, EPCs are based largely on standard assumptions rather than direct measurements of the building fabric. This renders EPCs alone as insufficient for heat pump design. 

Instead, designers must insist on more comprehensive building performance assessments. This should include detailed evaluations of a building’s thermal characteristics – including thermal bridging, airtightness, U-values, and overall envelope performance – to ensure a more reliable prediction of how well a heat pump will perform against its intended use. 

Only through these thorough assessments can designers confidently specify heat pump systems that will deliver on efficiency, comfort, and reliability.

Real-world performance

Comprehensive verification of the heat pump product is also critical. Heat pump manufacturers should provide credible energy labels supported by documentation detailing performance metrics based on robust testing. 

To ensure that a heat pump will work within a specific application, architects should request full test reports from accredited facilities to understand how performance is measured and the conditions in which the product has been tested. These test reports provide assurance that the heat pump will perform as intended and can include thermal performance testing in accordance with EN 14511 and EN 14825 as well as acoustic testing in accordance with EN 12102.

Independent laboratory testing, such as that provided by UKAS-accredited bodies, provide confidence in product claims and ensure they align with performance criteria and scheme requirements.

But beyond technical specification, a net-zero building also requires net-zero behaviour. Educating end-users about how to live with heat pumps is an important step for maximising performance and satisfaction. Unlike traditional gas boilers, heat pumps operate with longer running cycles and variable heating outputs meaning they require a behavioural shift in how indoor temperature is managed. 

For designers, integrating user education and clear guidance into the design and handover process is fundamental in supporting a successful transition. By doing so, they can help to encourage further uptake by framing energy savings as the primary incentive, with decarbonisation as a valuable byproduct.

Intent meets reality

Ultimately, for all heat pump system designs, a holistic approach is essential. 

In new build projects, any gap between design intent and as-built performance limits the operational performance of heat pumps, impacting efficiency and comfort. For retrofit installations, which pose their own challenges, diagnostic assessments of existing building conditions are fundamental to avoid costly oversights.

However, we shouldn’t be deterred. By embracing evidence-based specification, detailed diagnostics, and robust user education, designers have an opportunity to design buildings that will both ensure occupant wellbeing and support the drive to decarbonisation.