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EPC is not a reliable indicator of a property’s energy efficiency

A study of 10,000 properties by social housing data and insights company, Switchee, has found that Energy Performance Certificate scores (EPC) are not a reliable indicator of energy efficiency or heat retention in a property.
SS2023-1202. Tom Robins (1)
Switchee analysed real-time data captured by multiple sensors housed within its Switchee devices, which are installed in thousands of UK social housing homes. It measured the time taken for properties to lose 1°C of heat of internal air temperature when the heating was off. The data has revealed that the EPC rating of a home has no impact or correlation on the energy performance of that home.

Specifically, EPC A, F and G homes are the best-performing with an average Heat Loss Rate (HLR) of just under 6 hours. EPC C and D are the worst-performing homes with an average HLR of 4 hours (Table 1).

Table 1:

The study also found a wide gap in Heat Loss Rate (HLR) measurements with the worst-performing property losing 1°C of heat in less than an hour and the best-performing property losing 1°C of heat over 9 hours.

The impact a high Heat Loss Rate (HLR) has on the resident is that they heat their home for, on average, 1 hour and 48 minutes longer than those with a low Heat Loss Rate (HLR). In monetary terms this equates to an additional £1,576 per year in heating costs.

It’s a common belief that property archetype will impact its ability to retain or lose heat; for example, a mid-terrace will retain heat better than an end terrace. However, Switchee’s Heat Loss Rate (HLR) data demonstrates that it has very little impact. What does matter is the level of insulation and ventilation in the homes. Other impacting factors are the external weather in the area; homes in colder areas tend to lose heat quicker than those in warmer ones and property occupancy levels.

EPC scores have become an increasingly important focus for social housing landlords who are under pressure to meet new targets. Under the Clean Growth Strategy, targets have been set for social housing properties to reach EPC band C by 2030 for fuel-poor homes and by 2035 for all social housing. This study shows that energy efficiency targets may not be focusing on the right thing.

Instead by looking at a property’s Heat Loss Rate (HLR) score, housing providers are empowered to allocate retrofit measure resources to the properties that they know are most in need, rather than those they think should be. Furthermore, analysing Heat Loss Rate (HLR) before and after retrofit measures can accurately assess the impact of those retrofit measures using real data from the homes.

Switchee CEO, Tom Robins said: “We’ve analysed over 8 billion data points and these findings are a concern. While EPC scores measure the energy efficiency of a property by assessing various aspects of its construction, design and performance, our Heat Loss Rate (HLR) findings show the true effectiveness of insulation and the importance of an airtight property. It’s blown the premise that properties with a high EPC rating would lose heat the slowest, and vice versa, out of the water. Social housing providers must ask themselves if they are confident that they can rely on EPC ratings alone to assess the energy efficiency of their housing stock. Our data suggests not.”

Switchee has partnered with housing providers to develop the Heat Loss Rate (HLR) metric which is available via the Switchee analytics dashboard.

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