The UK's Complete Guide to the Home Energy Model
The UK Government's next-generation methodology for assessing the energy performance of homes — replacing SAP.
HEM uses half-hourly simulation across 17,520 timesteps per year, replacing SAP's monthly averages with dynamic thermal modelling based on BS EN ISO 52016.
17,520
Timesteps per year
Half-hourly
Simulation intervals
ISO 52016
International standard
Open source
Public codebase
| Feature | SAP 10.2 | HEM |
|---|---|---|
| Time Resolution | Monthly (12 periods) | Half-hourly (17,520 periods) |
| Thermal Zones | 2 fixed | User-defined |
| Heat Pump Modelling | Fixed COP values | Dynamic COP curves |
| Overheating | Simplified check | Full dynamic assessment |
| Solar PV | Annual yield | Half-hourly generation |
| Battery Storage | Not modelled | Charge/discharge cycles |
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HEM Status Dashboard
Current status of HEM and related systems
HEM Core Engine
Published (Open Source)
Oct 2025
FHS / SAP 10.3
SAP 10.3 Only at Launch
HEM follows 3+ months later
EPC Wrapper
Consultation
Expected 2026–2027
ECaaS Platform
Beta / Limited Access
Available Autumn 2025
Key Topics
What is the Home Energy Model?
A comprehensive guide to what HEM is, how it works, and why it matters for UK housing.
Future Homes Standard
Everything you need to know about the FHS, Part L changes, and compliance pathways.
SAP vs HEM Comparison
Side-by-side comparison of SAP and HEM methodologies, data requirements, and outputs.
Timeline & Status
Live tracker of HEM, FHS, and EPC reform milestones with current status indicators.
Glossary
A–Z reference of key terms with plain English and technical definitions.
EPCs & HEM
How Energy Performance Certificates are changing under the Home Energy Model.
News & Updates
Latest developments in HEM, the Future Homes Standard, and EPC reform.
Resources
Official documents, consultation archives, and tools for HEM and the FHS.
Frequently Asked Questions
What is the Home Energy Model?
The Home Energy Model (HEM) is the UK Government's next-generation methodology for assessing the energy performance of domestic buildings. It replaces SAP with a half-hourly dynamic simulation of energy use, carbon emissions, and running costs. Read our full introduction to HEM.
When does HEM come into effect?
The FHS will launch with SAP 10.3 as the sole compliance route, with HEM following a minimum of 3 months later. Once both are available, they will run in parallel for at least 24 months. See our Timeline & Status page for the latest dates.
What is the Future Homes Standard?
The Future Homes Standard is the forthcoming update to Part L of the Building Regulations, requiring 75–80% lower carbon emissions in new homes. It mandates heat pumps, solar PV, and enhanced fabric. Read our complete FHS guide.
The HEM Briefing
Regulation changes. Compliance deadlines. Industry analysis. Updates that matter for construction professionals — before they hit the mainstream press.
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From Guy Smith — DEA, SAP & SBEM Assessor since 2007.