Addressing the size of the problem
With government heat pump targets looming, and billions earmarked for retrofit funding, Stuart Fairlie,MD of Elmhurst Energy, argues that the UK must urgently address incorrect heat pump sizing by putting heat loss assessment at the heart of system specification – or risk damaging trust in low-carbon heating.
The UK government has set an ambitious target to install 600,000 heat pumps annually by 2028. But with fewer than half that number installed in total by late 2024, we’re not just falling short – we risk getting it wrong entirely.
There is growing evidence to suggest that many heat pumps being installed are incorrectly sized, meaning they are more likely to operate inefficiently and cost more to run, damaging public confidence in low-carbon heating. And with major government investment, such as the £1.29 billion in Wave 3 of the Social Housing Decarbonisation Fund, going on heat pump installations – it is vital to ensure the right sizes are installed.
Research assessing heat pump sizing across 56 homes carried out by Elmhurst Energy and Build Test Solutions (BTS) as part of the government’s Heat Pump Ready Programme found that the difference in heat loss between the calculated and measured was 35%. The calculated heat loss only matched the measured result for 30% of homes, meaning 70% were wrong. In the study, there was a bias towards overestimating the heat loss in 59% of houses. An oversized heat pump incurs higher costs – around 10% on average – and higher maintenance costs and lower running efficiency.
However, results showed there were also houses where the calculated heat loss was too low. These homes are at risk of having a heat pump installed that isn’t big enough to heat the house. Incorrect heat pump sizing can be prevented by measuring rather than using assumed calculations to produce a more accurate result for sizing and specifying heat pumps. To rapidly increase heat pump installations, each home needs an unobtrusive heat loss measurement to understand the heating level required.
Heat loss assessments
The current approach to specifying heat pumps relies on default assumptions about a building’s fabric and energy use, which are known to be prone to inaccuracy. This is handled mainly by installers and heating engineers, who are increasingly busy due to the surge in installations driven by government-funded initiatives.
This method isn’t reliable in the retrofit market, where the housing stock is highly diverse and little is known about its original construction, or building upgrades.
To help bridge the gap between design intent and actual, installed performance, measurement should be undertaken by energy assessors, who have a high knowledge of a building’s fabric. By making a change to the heat pump installation supply chain, this would reduce the burden on heat pump installers, allowing them to focus on system specification, quoting and installation.
Elmhurst recently introduced its Heat Loss Competency Scheme to support demand for more expertise in this area and deliver the right skills to increase heat pump uptake.
The EPC issue
While correct sizing is important in raising confidence in heat pumps, a major factor in the slow uptake is that they are not currently recommended in energy performance certificates (EPCs). This is because of the current EPC using a cost-based metric which simply indicates how expensive or cheap a property will be to run.
This is important because, at the moment, electricity is still more expensive than gas. Therefore, between a heat pump and a gas boiler, it is assumed that a heat pump will be more costly to run. This means heat pumps are unlikely to be recommended on the EPC and if one is installed, in some scenarios it could potentially lower the EPC.
Although location, property size, quality and type are the main pricing factors of a home, the energy efficiency rating also plays a role. Improving a property with an EPC rating of D to C could add three percent to the property’s value. This gives little impetus to homeowners to add a heat pump in the short term if they risk a lower EPC score.
The good news is that the Ministry for Housing, Communities and Local Government (MHCLG) released a consultation earlier this year which is proposing a number of new metrics that should be displayed on an EPC. This includes metrics such as energy use, carbon emissions, heating system type and fabric energy efficiency. Using these metrics would help to represent energy system upgrades, such as heat pumps, more fairly on the EPC.
We must act swiftly to change the EPC so that it does not penalise low-carbon heating solutions like heat pumps that run on electricity. The government must also take steps to switch the ‘green levy’ so it applies to gas rather than electricity supply. Making these changes, alongside the use of heat loss measurement to inform heat pump installations, will help to drive uptake.
