Energy Performance Certificates (EPCs)
EPCs are intended to enable homebuyers to compare properties’ energy efficiency. Homes are given a Standard Assessment Procedure (SAP) score between 1 and 100. The vast majority fall in the middle of the scale. This is then converted into an EPC rating between G and A. Both ‘current’ and ‘potential’ scores are given, with the potential value reflacting what could be achieved with a limited retrofit project.
So how useful are EPCs? Few would argue against having them, but their accuracy isn’t reliable. It’s possible to find EPC assessors advertising their services for as little as £40 online. For this price it’s unlikely that the assessor would even visit the property, let alone conduct a detailed survey. So how reliable can the result be? There are also known anomalies such as some homeowners achieving a lower score after replacing a gas boiler with a heat pump. Although the heat pump is more efficient, the EPC process considers electric heating to be less efficient than gas, hence the nonsensical lower score.
In February 2023, The Times reported a CarbonLaces study which compared EPC predictions against real-world energy usage from Smart Meters. The chart below shows the EPC-predicted energy usage in the blue bars, versus the actual recorded energy usage in yellow. Remarkably, there’s only a fractional difference in recorded energy usage between category A and G properties, despite the EPC prediction that the G-rated property will use over 15 times more energy. This demonstrates the wild inaccuracy of the EPC ratings.
In summary, we think the EPC process is well-intentioned but unreliable. The ratings should not be relied upon as a predictor of energy usage. If you’re undertaking a retrofit project you’ll probably be better off setting your requirements using one of the many energy efficiency benchmarks rather than targeting a particular EPC rating. If you’re buying a home and are interested in its energy use, why not ask the seller for a copy of their energy bills for the last year?