Government Seeks Views on Home Energy Model for Existing Homes
Alongside the Warm Homes Plan released by Government last week, the Department for Energy Security and Net Zero has set out plans to fundamentally reform how the energy efficiency of homes is measured and presented, proposing a new methodology the Home Energy Model, that would replace the current system used for Energy Performance Certificates (EPCs) for existing homes.
Under proposals published by the Department for Energy Security and Net Zero, the new Home Energy Model (HEM) would replace the long-standing SAP and RdSAP calculation methods used for EPCs in England and Wales. The changes are intended to provide more accurate, detailed and useful information to homeowners, tenants and landlords, while supporting the UK’s net-zero and fuel-poverty objectives.
What is the Home Energy Model?
The Home Energy Model (HEM) is the next-generation methodology being developed by Government to replace SAP. In it’s first release, it is being designed to allow compliance for the Future Homes Standard for new build dwellings, also known as the next update to Building Regulations. However, it is likely it will not be available as soon as the Future Homes Standard is released, and there will be a transitional period between an updated version of SAP (SAP 10.3) and the new Home Energy Model calculation methodology.
You can find out more on what HEM is and how it works here >
How does this affect Existing Dwellings and EPCs?
Although currently being developed for Future Homes Standard compliance, the Government are now proposing an expanded approach to use the Home Energy Model to generate Energy Performance Certificates for Existing Homes, as laid out in this consultation. Unlike SAP, the central HEM-Engine or calculation methodology, is controlled by Government, not developed by accreditation schemes. As an approved accreditation scheme, Elmhurst connects to an appropriate “wrapper” which defines the inputs and outputs from the HEM-Engine to adapt it for a specific purpose.
In the case of the above consultation, this will require Elmhurst connecting to an “Existing Home EPC Wrapper” to define the correct inputs and outputs for the EPC assessment.
The proposed Home Energy Model would use a more advanced, physics-based simulation of how homes use energy, with a modular data approach allowing assessors to input more detailed information where available, while still accommodating quicker, lower-cost assessments where data is limited. This is intended to address long-standing criticisms that current EPCs can be inaccurate or overly simplistic.
What is the consultation proposing?
A new methodology for assessing existing homes
The government is proposing a modular approach to inputting data under the Home Energy Model about existing dwellings during on-site assessments. Under this:
- Assessors can enter as much detail as they have available, module by module.
- Where detailed data is not available, simplified inputs or defaults would be used.
- This replaces the current “all-or-nothing” Reduced Data SAP (RdSAP) approach used for most existing homes.
New headline metrics for EPCs
- Fabric performance – how well the building’s structure retains heat.
- Heating system performance – efficiency and carbon intensity of space/heat systems.
- Smart readiness – ability of the home to use smart energy technologies (e.g., controls, generation/storage).
- Energy cost – predicted annual energy costs, with proposals to present this in £ rather than just bands.
- Each metric would be expressed as a 1–100 score and grouped into A–G bands (except energy cost, which may be shown in £ for clarity)
- To aid transition, the current “legacy” EPC score (the old headline energy efficiency rating) would still be shown on certificates until at least the end of 2029, even as the new metrics are introduced
Proposed rules within the metrics
- No home with a solely fossil-fuel heating system would be able to achieve a C or higher on the heating metric; low-carbon systems (like heat pumps) would score better.
- Electric cooking and renewable generation (e.g., solar) could improve smart readiness and overall performance.
- The inclusion of additional technology ie SMETERS
Naming the Modular HEM Approach
The government is asking for views on renaming a modular version of HEM so it’s clear, reflects flexibility, and avoids confusion with full HEM and legacy RdSAP. They want feedback on the suggested names as below:
- HEM for Existing Dwellings (HEMEX)
- HEM Input Expansion (HEMIE)
- Mixed Data for HEM (MdHEM)
- Reduced data HEM (RdHEM)
What does the Government want feedback on?
As part of this consultation, Government are looking for feedback on the following:
- How the new metrics should be calculated and scored
- How band thresholds should be set, in particular achieving Band C for MEES.
- How performance improvement advice should be presented to homeowners and landlords.
Elmhurst are preparing a response to this consultation and will share it with members in due course. The deadline for submission is Wednesday 18th March and we would encourage any members or companies involved in the Domestic Energy Assessment sector to respond.
The Home Energy Model: Energy Performance Certificates
You can find the full version of the consultation below along with how you can respond. The deadline for responses is Wednesday 18th March 2026.
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