Home Energy Model (HEM)
The Home Energy Model (HEM) is the new government-approved methodology for calculating the energy performance of existing homes, developed to replace the Standard Assessment Procedure (SAP) that has underpinned Energy Performance Certificates since 1995. HEM was developed as part of a broader reform of the Energy Performance of Buildings framework and will eventually power all domestic EPC assessments in England and Wales. On 9 March 2026, the government confirmed that HEM-based EPCs would launch in the second half of 2027, delayed from the original late 2026 target to allow assessors, software providers, and the wider supply chain more time to prepare.
Why SAP is being replaced
The current SAP/RdSAP methodology calculates EPC ratings primarily on the basis of estimated energy costs, the cost of heating, lighting, and hot water using a standardised set of fuel price assumptions. This approach has a well-known limitation. It can reward cheaper fuels over cleaner ones, meaning a property with an inefficient gas boiler may score better than a more genuinely energy-efficient property using low-carbon heating simply because gas is currently priced as cheaper than electricity per unit. HEM shifts the primary metric from energy cost to physical energy performance, specifically how much energy a property consumes and how effectively it retains heat.
HEM also operates using half-hourly dynamic simulation (17,520 timesteps per year) rather than SAP's simplified monthly averages, producing more accurate predictions of a property's real-world energy behaviour across different seasons, occupancy patterns, and heating schedules.
The four HEM metrics
Under the new framework, compliance with MEES from 1 October 2030 will be assessed against two of four metrics. The first is mandatory; the second is a landlord's choice from two options.
Fabric Performance (mandatory). Measures how well the building retains heat through its insulation, windows, and construction. This is the "fabric first" metric, every landlord must demonstrate the property meets the band C standard on fabric before anything else is considered. Improvements that directly address fabric performance include loft insulation, cavity or solid wall insulation, floor insulation, and double or triple glazing.
Heating System (choice one). Assesses the carbon intensity and efficiency of the primary heating system. Gas boilers are expected to score poorly on this metric; heat pumps and other low-carbon heating systems are designed to score well. A landlord who meets fabric performance and then also meets the heating system standard will be compliant.
Smart Readiness (choice two). Measures the property's capacity for smart energy management, including solar panels, battery storage, smart thermostats, and other technologies that allow the property to interact with and respond to the energy grid. This metric offers an alternative compliance route for landlords who cannot practically install a heat pump.
Energy Cost (informational). An estimated running cost figure for the property, retained as a consumer-facing information metric but not used for MEES compliance.
The exact band boundaries for each metric, what scores will constitute a band C under HEM, are subject to the consultation that closed in March 2026. The government's final response confirming thresholds is expected later in 2026.
Timeline and transition
HEM-based EPCs are expected to launch in H2 2027. During a transition period running from H2 2027 to 1 October 2029, both SAP-based and HEM-based assessments will be valid, and landlords can choose either methodology when commissioning a new EPC. From 1 October 2029, SAP is discontinued and all new EPC assessments must use HEM. Properties that hold a valid EPC C under either the current SAP system or HEM before 1 October 2029 will be treated as MEES-compliant until that certificate expires, typically ten years, giving early movers a significant advantage.
The key practical implication is this. A landlord who achieves EPC C under the current SAP methodology before 1 October 2029 is compliant until their certificate expires, even if a HEM-based assessment of the same property would produce a different result. This creates a meaningful window for landlords to improve properties and lock in compliance under the more predictable current system.
For the full context of what MEES requires and how the 2030 deadline works, see the August definition of Minimum Energy Efficiency Standards and the August MEES guide for landlords. For a plain-English explanation of the EPC itself and what a landlord must do with it, see the August definition of the EPC.
Frequently asked questions
When will HEM replace the current EPC methodology?
HEM-based EPCs are expected to launch in H2 2027, delayed from the original late 2026 target. The transition period runs until 1 October 2029, when SAP is discontinued. From that point, all new EPC assessments must use HEM. The 2030 MEES compliance deadline is unaffected by the methodology change.
Will properties that currently have EPC C need reassessment under HEM?
Not immediately. A valid SAP-based EPC C obtained before 1 October 2029 is treated as MEES-compliant until it expires (up to ten years). However, when that certificate expires, the property will be assessed under HEM, which may produce a different result, particularly for gas-heated properties, which tend to score poorly on the HEM heating system metric.
