Energy Performance Certificates (EPCs) are about to be calculated in a very different way as the government prepares to launch the Home Energy Model (HEM), which will replace the current Standard Assessment Procedure (SAP) used since 1993.
The government says HEM is designed to provide more detailed calculations of energy use, including heating, hot water, solar panels and smart home technologies.
While the Future Homes Standard is still due to be introduced in early 2026, HEM will now follow at least three months later, meaning millions of homes will be assessed under the new model.
What the Home Energy Model is and how it works
According to the government, HEM calculates energy use at 30-minute intervals, compared with the monthly averages used by the current SAP system.
The government says this will allow the model to take account of factors such as room temperatures, heat loss through walls or windows, shading from other buildings, and the performance of heating systems, including heat pumps.
HEM is initially being developed to check whether new homes meet the Future Homes Standard, but the government plans for it to eventually be used for EPC calculations.
Timeline and implementation
The government has confirmed that HEM will not launch at the same time as the Future Homes Standard.
The Future Homes Standard rollout is still planned for the first quarter of 2026, and SAP 10.3 will remain the official method for EPC calculations until HEM is ready. HEM is now expected to follow at least three months later.
Officials said the delay is intended to ensure the model is “as robust as possible and delivered to the highest possible standard,” giving assessors, developers and homeowners time to prepare for the change.
What this means for homeowners and EPCs
Once HEM is live, the government says EPCs will be calculated using the new methodology, which could change the ratings for millions of homes.
SAP 10.3 will continue to be used until HEM is implemented. The government says the new model is designed to support the Future Homes Standard and future energy performance assessments, though exactly how ratings may change in practice remains to be seen.
