From 2027, the familiar A to G energy rating is being rebuilt. A new calculation engine, the Home Energy Model, replaces SAP and RdSAP, and the single cost-based score gives way to four separate metrics with a dual compliance test for rented homes. Here is what changes, what a C is likely to look like, and the one protection every landlord should know about.

Why the rules are changing

The reform is not really about tougher paperwork. The government's argument is that a single cost-based rating was too crude: it told you a property was a "D" without telling you why, and because it was built on running costs it could penalise a home for installing a heat pump simply because electricity costs more per unit than gas. Breaking the rating into separate metrics gives owners clearer, more actionable information.

The stated aims are warmer homes, lower bills, less fuel poverty and progress toward net zero. They sit inside the Warm Homes Plan, backed by up to £15 billion of public funding intended to support upgrades in up to five million homes over five years. The starting principle throughout is "fabric first": insulation and airtightness before heating, because a home that loses less heat is warmer, cheaper to run and a better base for whatever heating comes next.

The four new metrics

Fabric performance

The building's thermal performance: insulation levels, window quality and airtightness. Broadly the thing most people assume an EPC already measures, now isolated as its own metric, evaluated using the Fabric Energy Efficiency methodology adapted from new-build regulations. The government proposes to keep the new C/D boundary closely equivalent to the current one.

A newer idea sits alongside: Smart Meter Enabled Thermal Efficiency Ratings (SMETERs) estimate heat loss from real metered energy use and indoor/outdoor temperatures, rather than a simulated model. Research has shown SMETER measurements can sometimes be more accurate than the modelled approach, and the government proposes letting owners voluntarily record validated SMETER results alongside the modelled figure. If you suspect a property performs better than a cautious survey suggests, real measurement is becoming a route to evidence it.

Heating system

An assessment of the technologies generating heat for space heating, hot water and cooking, scored on efficiency and carbon. The proposed banding is blunt: no home relying on a primary fossil-fuel system, such as a gas boiler, is expected to achieve a C on this metric. Heat pumps and low-carbon heat networks would always score C or above; hybrids with fossil fuels score D or below; direct electric heating without storage scores D or below, though storage systems using off-peak electricity can reach C.

Smart readiness

The building's potential to generate its own energy and shift demand: smart meters, solar PV, batteries, thermal storage, smart heating controls, EV charge points and the quality of the grid connection. The scoring approach is still in consultation, but a modest solar array plus a smart meter is the working shape of a C.

Energy cost

An estimated annual energy bill in pounds, shown for tenant information. It is not part of the compliance test.

The dual-metric test

Instead of one overall band, a rented home must satisfy two standards. Fabric performance is primary: meet it, or register a valid exemption against it, before anything else. Mechanically it really does come first: spend on smart readiness doesn't count toward your cost cap until fabric is met or exempted.

Then comes the second leg, and the choice is the landlord's: heating system or smart readiness. This choice is what protects the working gas boiler. A boiler won't pass the heating metric, so in practice a landlord keeping one complies via fabric plus smart readiness: solar PV, battery storage or smart controls. The government has gone a step further and confirmed that where a property cannot take any recommended smart readiness measure, an overshadowed or unsuitable roof for example, the landlord is not then required to fall back on the heating standard either. You can never be forced into a heat pump to comply. How that "cannot take any measure" test is evidenced will come with the 2027 regulations, so a little caution until then.

Two nuances catch people out. First, it is genuinely a dual test: an exemption on one leg does not excuse the other, so hard-to-treat properties may end up registering two. Second, only fabric plus your chosen secondary are compliance metrics; energy cost is informational.

What the new C might look like

Fabric: a heat loss parameter of 3 W/m²K

The government's impact assessment proxies a fabric C at a heat loss parameter of 3 W/m²K: the rate of heat loss per degree of temperature difference, per square metre of floor. Lower is better, and for context a Passivhaus sits around 0.8. So 3 is not an eco-standard; it's a "the basic fabric is sound" bar. A property with loft insulation topped to 270mm, walls insulated, draughts sealed and reasonable glazing will typically land at or under it. The homes that miss are the predictable ones: solid-wall, older, hard-to-treat stock, which is exactly where exemptions will cluster.

Smart readiness: at least 1 kWp of solar, where suitable

1 kWp is a very small array, roughly two or three modern panels, when a typical domestic installation is 3 to 5 kWp. The proxy is essentially "has a modest solar system". The phrase carrying the weight is "where suitable": orientation, pitch, shading and structure have to allow it, which rules out some flats and poorly-oriented roofs. Remember the metric is broader than solar: smart meters, controls, batteries and EV-charging readiness also count.

Treat both proxies as directional modelling assumptions, not final bandings, until the Home Energy Model consultation concludes.

What this means for spending decisions now

Fabric improvements count under both today's rating and tomorrow's fabric metric; they are the closest thing to a no-regrets investment and most are cheap. Measures that only flatter the current cost-based score without improving fabric deserve more care until the rules are final. Before committing to anything big, have a qualified assessor model your specific property under both methodologies; the gap between a well-chosen measure and a poorly chosen one is the difference between clearing a band boundary and wasting four figures.

For the full picture, deadlines, costs, grants and the action checklist, see our cornerstone guide: EPC rules for landlords: what you need to do now.

Want to know where your property stands? Order an EPC for £95.

This reflects confirmed policy intent as at mid-2026; final regulations are expected in 2027. General guidance, not legal or financial advice.