The Department for Energy Security and Net Zero (DESNZ) has published the government's response to its consultation on the Home Energy Model, the replacement for the Standard Assessment Procedure (SAP)1. The response confirms the design decisions taken since the consultation closed1.
The model will be called the Home Energy Model (HEM), and the calculation will be undertaken centrally, with the Schemes providing front-end software for assessors1. It is based on British and EU standards, and a 30-minute time step resolution is confirmed1. The Future Homes Hub, an independent body, describes HEM as "not an evolution of SAP, it is a whole new model"1. The consultation on HEM was separate from the Future Homes Standard consultation and focused on the design and function of the SAP replacement, accompanied by a consultation version of the software1.
"HEM is not an evolution of SAP, it is a whole new model"
Compared with SAP, a greater number of product categories are included, such as cylinders, and products that were in SAP Appendix Q are being included in the main model1. An updated version of the Appendix Q procedure will allow new products to be added1. Since the consultation, ventilation and infiltration have been reworked, storage heater and heat battery models updated, the types of heat pumps included expanded, solar PV and electric battery models reworked, and hot water demand and storage improved1. The model is still being tested and validated1.
| Area | Change confirmed |
|---|---|
| Model name | Home Energy Model (HEM)1 |
| Calculation | Undertaken centrally, Schemes provide front-end software1 |
| Standards basis | British and EU standards1 |
| Time resolution | 30-minute time step1 |
| Products | More categories than SAP, including cylinders; SAP Appendix Q products moved into the main model1 |
| Since consultation | Ventilation and infiltration reworked; storage heater and heat battery models updated; more heat pump types; solar PV and electric battery models reworked; hot water demand and storage improved1 |
Why it matters for households
The Home Energy Model is the calculation engine that will sit behind energy performance certificates and compliance checks for new homes, so its design decisions shape how a home's efficiency, running costs and carbon are scored. A central calculation with assessor software on top changes how assessments are produced, and the wider product list, including cylinders and former Appendix Q products, means more installed equipment can be represented in the model. The 30-minute time step and reworked heat pump, battery and hot water models matter for homes with those technologies, because they affect how a home's energy use is estimated over a day rather than as a single annual figure. The Future Homes Standard will set the rules that HEM is used to check against.
What happens next
The Future Homes Standard legislation and further Home Energy Model detail are due to be published later this year, according to the Future Homes Hub1. The model is continuing to be tested and validated1.
Sources1 cited
- HEM Consultation - Government Response Published, futurehomes.org.uk