Heat pumps and your EPC rating

How a heat pump is recorded in the assessment

An EPC for an existing home is produced using RdSAP, a reduced-data version of the government’s standard assessment procedure, carried out by an accredited Domestic Energy Assessor; new builds are assessed using full SAP instead. The assessor records the main heating system and its fuel, the hot water arrangement, the emitters and the controls. A heat pump is entered as the main heat source, and the software applies an efficiency figure taken from the methodology or, where the paperwork supports it, from recognised product data.

The finished certificate is lodged on the national register and a domestic EPC is valid for ten years, although a new one can be commissioned sooner if work has been carried out and you want the change reflected. A reassessment is usually charged somewhere in the region of £60 to £120, though prices are not fixed and vary with the size of the property, the area and the assessor. Our guide to getting an EPC explains how a visit is arranged and what the assessor looks at.

The assessment is standardised. It assumes a typical household, a typical heating pattern and typical internal temperatures, then models the property on that basis. It is not a measurement of your bills or your habits, and two identical houses run very differently will still receive the same certificate.

The headline rating is built on cost

The A to G efficiency rating on an EPC – A being 92 to 100 and G being 1 to 20 – is derived from modelled energy cost, expressed relative to floor area. That single design decision explains most of the confusion around heat pumps. The band responds to what the modelled energy is expected to cost, not to the carbon it produces and not directly to the kilowatt hours it uses.

A well-designed heat pump delivers several units of heat for each unit of electricity it uses, which no boiler can match. Electricity in the UK is generally priced above gas for each unit bought, however, so the efficiency advantage and the price difference push in opposite directions and much of the gain is absorbed before it reaches the cost figure. Where a modern gas boiler is being replaced, the band may move only slightly, or not at all. No one can promise you a particular band from an installation, and any quotation that does should be treated with caution.

The environmental score often tells a different story

The assessment also produces a separate environmental impact rating, based on modelled carbon dioxide emissions and expressed on the same A to G scale, though it is not always given the same prominence as the efficiency band on the certificate itself. Because grid electricity has become cleaner as more low-carbon generation has come online, heat pumps tend to look comparatively strong on that measure even where the cost-based band is unchanged. Seeing the two scores diverge is normal.

That divergence follows from what each score is designed to measure. It is not evidence that a heat pump is a poor choice, and the certificate is not passing judgement on the technology. Our guide to understanding your EPC explains both scales and the rest of the document.

Understand the fabric and the heat demand first

How much heat a house loses on a cold day governs everything that follows: the size of unit required, the temperature it has to run at, and the running cost. Loft and wall insulation, draught-proofing and glazing all reduce that demand. Dealing with the obvious fabric weaknesses before specifying a system usually produces a smaller, quieter installation that runs more efficiently for the rest of its life. Our guide on how to improve your EPC rating covers the fabric measures in more detail.

An EPC is a screening document, not a heat loss survey: it works from standard assumptions and, where a construction detail cannot be seen, from defaults. Sizing should rest on a room-by-room heat loss calculation for your actual house, not on figures printed on a certificate.

Older and protected buildings need particular care. Whether a listed building or one in a conservation area falls outside the EPC requirement depends on the circumstances and on whether compliance would unacceptably alter its character or appearance, so the position is not automatic and should be checked on gov.uk and with your local authority. Listed building consent or planning permission may in any case be needed for external plant. Our guide to EPCs for older homes sets out the wider difficulties with traditional construction.

Emitters, flow temperature and controls

Heat pumps are at their most efficient running at a low flow temperature for long, steady periods. Delivering the same warmth at a lower temperature means larger emitters: bigger radiators in some rooms, or underfloor heating where that is practical. If undersized radiators are left in place, the system has to run hotter to keep up, efficiency falls and running costs rise.

Controls matter for the same reason. Weather compensation, a well-insulated cylinder of the right size and sensible zoning all help the system hold a low temperature rather than cycling. Some system and control features are recognised within the assessment, but only where the assessor can see them or documentation supports the entry, so keep the design paperwork, commissioning records and installation certificates to hand.

Grants, rules and where things differ

Government support for low-carbon heating exists, but schemes, eligibility rules and amounts change over time and differ between the nations of the UK. Rather than rely on figures quoted by an installer, check the current position on gov.uk before you budget for anything; the energy grants calculator is a sensible starting point. What follows is general information rather than financial advice, and it is worth taking independent advice before committing to any funding arrangement.

Landlords have a further reason to pay attention. Under the minimum energy efficiency standard, since 1 April 2020 a private landlord in England and Wales may not let a domestic property rated below band E unless a valid exemption is registered. Proposals to raise that minimum to band C have been consulted on but are not settled law, so treat any firm date you are quoted as unconfirmed and check the current requirements on gov.uk. Our guide to EPC rules for landlords covers the standard and the exemptions register in more detail.

Energy performance is a devolved matter. Scotland and Northern Ireland have their own assessment arrangements, their own rules for rented housing and their own support schemes, so guidance written for England and Wales will not always apply. Our guide to EPCs across the UK explains where the differences sit.

Getting the right advice

A heat pump is a design job rather than a product swap. The difference between an installation that performs as intended and one that disappoints is almost always the quality of the heat loss work, the emitter sizing and the commissioning. Use a suitably qualified designer or installer, ask to see the calculations, and be wary of anyone offering a specification without measuring the house.

EPC Checker is a research aid built on published EPC data. It is not an assessment, a survey, or professional, legal or financial advice, and nothing here replaces a design carried out for your property by a qualified professional.