TL;DR:
- The reformed EPC methodology (rolling out 2026) uses actual energy costs and carbon intensity rather than the old SAP points system, making ratings more meaningful for modern low-carbon technology
- Heat pumps, solar PV, and fabric improvements now score significantly better than under the old system — some homes upgrading to heat pumps jumped two EPC bands
- Rental landlords face a legal minimum of EPC C by 2028 for new tenancies, with all tenancies following in 2029 — the new methodology makes reaching C more achievable for many properties
Energy Performance Certificates have long been criticised as poor guides to real-world energy costs. The old Standard Assessment Procedure (SAP) methodology rated gas boilers favourably because it valued cheap fuel costs over carbon emissions — which meant a gas-heated home could outscore a heat pump home even as energy costs flipped. The reformed methodology, being phased in throughout 2026, fixes this and a lot more.
If you own property, rent, or are planning a retrofit, understanding the new system matters more than ever.
What Changed in the Methodology
The previous SAP-based EPCs expressed performance as a number from 1–100, translated into grades A–G. The calculation weighted fuel costs heavily, which penalised electric heating (including heat pumps) because electricity was more expensive per kWh than gas. It also undervalued solar PV, fabric insulation, and thermal mass.
The reformed methodology, developed by BRE Group and adopted by DLUHC, makes several significant changes:
Metric shift. The headline metric shifts from a fuel cost index to a combination of actual energy demand (kWh/m²/year) and carbon intensity. This means a home with a heat pump drawing electricity from an increasingly low-carbon grid scores well on both — without being penalised for electricity’s price premium over gas.
Time-of-use awareness. The new methodology incorporates smart tariffs and time-of-use flexibility. Homes with battery storage or smart controls that shift consumption to low-carbon periods score better than identical homes without them.
Solar PV integration. Under the old system, solar panels often improved ratings only modestly because the benefit was calculated against a low-value fuel cost baseline. The new system credits solar generation against both energy demand and carbon, which can improve a band on its own for a reasonably sized installation.
Fabric first, properly. Wall insulation, loft insulation, and window performance are now weighted more heavily and measured against actual U-values rather than assumed construction standards. This benefits older properties where the as-built specification was conservative.
How Much Have Ratings Changed in Practice?
The government’s own modelling and early assessor reports suggest meaningful shifts for properties with low-carbon technology installed:
- Gas boiler homes in the D or E band largely stay where they are or dip slightly, since the cost-based benefit of cheap gas no longer inflates their score
- Heat pump homes that were scoring C under the old system are often scoring B under the new one, because the carbon and efficiency metrics both favour heat pump performance
- Homes with solar PV and battery storage have seen the most improvement — some properties moved two full bands, from D to B, when solar, battery, and improved insulation were combined
- Victorian terraces with solid walls remain hard to improve without significant investment, but the new methodology’s clearer separation of fabric vs. heating system makes the improvement pathway more legible
The practical effect: if you’ve installed a heat pump or solar in the last few years and your EPC was assessed under the old methodology, it’s worth commissioning a new assessment. You may find your rating is materially better than your certificate shows.
What It Means for Landlords
The Minimum Energy Efficiency Standards (MEES) regulations require rental properties to reach EPC C for new tenancies from April 2028, and for all tenancies from April 2029. This has been a source of significant anxiety for landlords, particularly those with older housing stock.
The reformed methodology helps in two ways. First, properties that have already had heat pump or solar upgrades will see improved ratings that may already put them at or above C without further work. Second, the clearer marginal improvement weighting makes it easier for assessors and landlords to identify the most cost-effective path to C for specific property types.
For a typical 1960s semi-detached with a gas boiler and loft insulation already done, the most efficient path to C is usually:
- Air source heat pump (often the single biggest improvement under the new methodology)
- If needed: cavity wall insulation
- If needed: solar PV (3–4kWp)
Landlords starting from F or G will need to engage with the £10,000 spending cap (properties can be exempt if the cost of reaching C exceeds £10,000 even after grants). The government has indicated this cap will be revised alongside the ECO5 grant scheme.
What Home Buyers Should Know
If you’re buying a property and the EPC was issued before 2026, treat it as a rough indicator rather than an accurate assessment. Post-reform ratings are more reliable for comparing properties and estimating actual running costs.
The new EPCs also include a more detailed breakdown page showing which individual measures would bring the most improvement — more useful than the old “recommended improvements” section, which often suggested measures that had minimal impact on the headline rating.
Getting an Updated Assessment
New EPCs cost between £60–150 depending on property size and assessor. If your property has had significant energy improvements (heat pump, solar, insulation) in the last 3 years and the certificate predates the new methodology, a reassessment is likely to pay for itself — particularly for landlords facing the MEES deadline and homeowners whose property value may be affected by the rating.
The Domestic Energy Assessors Register (DESAR) and the energy assessor registers at Elmhurst Energy and Stroma are the starting points for finding an accredited assessor. Only lodged certificates (on the national EPC register) are legally valid for property transactions and planning purposes.
The reformed system is a genuine improvement. For anyone invested in low-carbon retrofits, it’s long overdue.