Overview

The Home Energy Model (HEM) is the UK Government’s next-generation methodology for assessing the energy performance of domestic buildings. Scheduled to replace the Standard Assessment Procedure (SAP) in 2025, HEM delivers a half-hourly dynamic simulation of a home’s energy use, carbon emissions and running costs—ensuring assessments that better reflect real-world performance and emerging low-carbon technologies.

Purpose & Policy Context

HEM was developed to support the UK’s net-zero ambitions by providing a robust, physics-based tool which:

• Underpins the Future Homes Standard (2025)
  Demonstrates that every new home meets “zero-carbon ready” targets under Part L of Building Regulations.
• Reforms the EPC regime
  Lays the foundation for a more accurate Energy Performance Certificate that reports energy consumption, carbon and cost on a consistent basis.
• Supports retrofit and grant programmes
  Supplies high-confidence predictions of savings, helping both homeowners and funders target the measures that deliver real carbon and cost reductions.
• Aligns with net-zero policy
  Rewards uptake of heat pumps, solar PV, battery storage, smart controls and other carbon-saving technologies by modelling their performance in detail.

Key Features

• Half-hourly dynamic engine
  Simulates every 30-minute timestep across a full year to capture daily and seasonal energy flows.
• Modular architecture
  Separates fabric, heating, ventilation, renewables and system modules—each easily updated or replaced.
• Physics-based calculations
  Follows international standards (BS EN ISO 52016-1:2017) for heat balance and dynamic thermal modelling.
• Advanced technology modelling
  Represents heat pump COP variation, MVHR performance, PV generation and battery charge/discharge behaviour.
• Open-source code
  Published publicly so stakeholders can inspect, validate and contribute to the model.
• Centralised calculation service
  A cloud-hosted API ensures all assessors use the identical, up-to-date engine.

Timeline

• December 2023 – HEM core and Future Homes Standard “wrapper” consultations launched
• March 2024 – Consultations closed; feedback analysed and validation continued
• Late 2024 – Final HEM specification and government response published
• 2025 – HEM mandated for new-build compliance under Part L; pilot EPC scheme begins
• 2026 – Full rollout of HEM-based EPCs across England, Wales and Northern Ireland

Governance & Continuous Improvement

HEM is maintained by the Department for Energy Security & Net Zero (DESNZ) in collaboration with the Building Research Establishment (BRE). Its open-source, modular design enables:

• Transparent updates – All code changes and validation results are publicly logged.
• Community input – Academia, industry and assessors can propose enhancements or new modules.
• Ongoing validation – Continuous benchmarking against monitored data and leading simulation tools preserves accuracy as technology and evidence evolve.

Learn More & Get Involved

For the full technical details, validation reports, code repository and case studies, please visit:

• Technical Details – Methodology, algorithms and module descriptions
• Consultation Archive – Original consultation papers, responses and government outcome
• Case Studies – Worked examples ranging from new-build to retrofit scenarios
• FAQ – Common questions about using and interpreting HEM