EPCs are being rebuilt. Here is what the Home Energy Model changes.
From the second half of 2027, the way your home’s energy performance is measured changes more than it has at any point since certificates began in 2007.
A different engine underneath, and a different certificate on top.
RdSAP, the method behind EPCs for existing homes today, works on monthly averages and a large set of age-based default assumptions. It was designed as a practical compromise: produce a usable certificate without needing construction drawings for every house in the country.
The Home Energy Model, or HEM, is a physics-based simulation. It models how a building gains and loses heat in half-hourly steps, and it separates the calculation engine from the policy sitting on top of it. In plain terms, it reflects what your property actually does, rather than what a lookup table assumes a property of that age normally does.
It changes the survey too. Instead of rigid defaults, the assessor records what can genuinely be observed and uses simplified inputs only where they cannot. Surveys take longer, and the quality of the survey starts to matter a great deal more than it does today.
The single A to G score is being split apart.
| New metric | What it measures |
|---|---|
| Fabric performance | How well the structure holds heat: walls, roof, floors, glazing, draughts |
| Heating system | The efficiency and the carbon intensity of the heat source |
| Smart readiness | How well the home can store, shift and manage its energy use |
| Energy cost | An estimated annual running cost figure |
The Energy Efficiency Rating you already recognise is expected to run alongside the new metrics until at least late 2029, so there is no cliff edge, and certificates already issued stay valid for their full ten years.
Read this bit twice.
Let that sink in for a minute. A brand new, top of the range, high efficiency condensing gas boiler will not reach band C.
Not on the heating system metric. Not if it was fitted last week. Not if it is the best appliance on the market. Under the proposals consulted on in January 2026, gas, oil and LPG heating is capped at band D, and that cap is expected to apply to hybrid systems too.
Roughly 24 million homes in this country are heated by a gas boiler.
Why a better appliance cannot save you
Because the metric is not measuring the boiler. It is measuring the heat source, which means efficiency and carbon intensity together.
A condensing boiler is already close to the physical limit of what burning gas can achieve, so there is no meaningful headroom left in the appliance. Meanwhile the electricity grid gets cleaner every year and gas does not. The ceiling is a property of the fuel, not of the kit. Buying a better boiler moves you along a scale that has already run out of road.
Heating system metric only, as proposed. Fabric, smart readiness and cost are scored separately.
What this does not mean
It does not mean your boiler becomes illegal, or that anybody is coming to remove it. If you own and live in your home you are under no obligation to change a working heating system, and a band D on one of four metrics is not a failure notice.
What it does mean is that from 2027 the certificate stops flattering fossil fuel heating. That will show up when you sell, when you let, and increasingly in how buyers and lenders read a property.
If you let property, it bites harder
The proposed route to the 2030 private rented sector standard is a fabric-first dual test: reach the standard on fabric performance, then on either heating system or smart readiness.
Since a gas boiler cannot deliver the heating system half, a landlord keeping the boiler has one route left, and it runs through smart readiness: solar, storage, smart controls and metering. That is a real and legitimate route. It is also a very different shopping list from the one most landlords have been planning around, and the fabric half is not optional either way.
Fabric stops hiding behind kit.
Today a well-specified heating system can carry a leaky building to a respectable rating. With fabric scored on its own, poor insulation becomes visible in its own right, and a heat pump can no longer paper over a draughty house on paper.
The flip side is better news than it sounds. Solid older properties with decent fabric and tired heating have been marked down unfairly for years. They will finally get credit for the part that is genuinely hard to change.
The measure that counts under both the old rules and the new ones is the one nobody knocks on your door to sell.
Four things that are safe to act on today.
The honest answer first: nobody can model a HEM score for your property yet. The consultation closed in March 2026 and the final thresholds have not been published. Anyone quoting you a guaranteed future rating is guessing, and the launch date has already moved once.
Fix fabric first
Insulation, glazing and draught proofing count under the current rules and under every proposed version of the new ones. There is no scenario where they become worthless.
Do not panic-replace a working boiler
Think about the order of works, and about whether the smart readiness route suits your property better than a heat pump does. Ripping out a boiler that has years left in it is rarely the cheapest answer.
Be wary of anything sold on “the rules are changing”
That line is about to be used very heavily on doorsteps and over the phone. A genuine recommendation survives being questioned. A sales script does not.
Get a proper survey before you spend
Under a model that rewards accurate data about your actual building, a rushed assessment costs you real money. This is the change that most rewards getting the survey right.
Someone on your side of the table.
I am a Domestic Energy Assessor and PAS 2035 Retrofit Assessor working across Shropshire and the West Midlands. I do not install anything and I do not sell equipment, so my view on what to do, and in what order, is not tied to a product.
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See what is includedBased on the government’s Home Energy Model consultation on EPC assessment (January 2026), the partial government response on reforms to the energy performance of buildings regime, and the March 2026 update moving the launch to the second half of 2027. Band thresholds remain proposals until the full government response is published. This page will be updated as the position is confirmed.
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Tell me the site, the running costs if you know them, and what has forced the question. Fifteen minutes will usually tell us both whether there is enough here to be worth a survey.