Heat pumps and EPC ratings: what actually changes on the certificate

Air source vs ground source for EPC purposes

Air source heat pumps extract heat from outside air and are by far the more common installation in UK homes, being cheaper to install and requiring only an external unit rather than ground works. Ground source heat pumps extract heat from buried loops or boreholes, achieve a higher and more stable coefficient of performance because ground temperature varies less than air temperature through the year, but cost substantially more to install because of the excavation or drilling required. Both types are recorded in RdSAP using their rated efficiency, so the certificate will reflect a ground source system's typically higher efficiency figure, but the extra installation cost rarely makes ground source the right choice purely for an EPC band improvement.

Evidence the assessor needs

Heat pumps are recorded in RdSAP using data such as the manufacturer, model, rated output and efficiency, which the assessor needs documented evidence for rather than a general description from the homeowner. An MCS (Microgeneration Certification Scheme) installation certificate is the standard form of evidence and should be kept alongside the building regulations compliance certificate issued for the installation. Where a system was installed under a grant scheme such as the Boiler Upgrade Scheme, the paperwork retained for that application is usually sufficient too.

What we see on assessments across London and the Home Counties

In practice, heat pumps installed into recently built or well-retrofitted homes with good fabric and correctly sized emitters produce a clear improvement across both ratings, often moving properties comfortably into band B or A on the environmental impact score. In older stock, particularly solid-wall Victorian and 1930s houses without prior fabric upgrades, we more often see the environmental impact rating improve noticeably while the energy efficiency rating moves only slightly, stays flat, or occasionally dips relative to an efficient modern gas boiler, purely because of the relative cost of electricity versus gas built into the standard RdSAP fuel price assumptions used at the time of assessment.

• Well-insulated new-build or retrofitted homes: strong improvement on both scores is typical
• Older solid-wall homes with no prior fabric work: environmental score improves, cost score is variable
• Undersized radiators left in place after a heat pump switch: efficiency losses that show up as poor real-world performance and can be visible in the assessment
• Hybrid systems (heat pump plus existing boiler) need to be recorded correctly or the model will misrepresent actual running patterns

Landlords weighing heat pumps against MEES

For landlords working towards EPC C for MEES compliance, a heat pump is not automatically the most cost-effective single measure, because its main strength on the certificate is the carbon score, while MEES compliance is driven by the overall energy efficiency band. Cheaper fabric measures — loft insulation, cavity wall insulation where applicable, heating controls, and low-energy lighting — often move the energy efficiency rating further per pound spent than a heat pump does on a property that has not yet had those improvements. A heat pump is more likely to be the measure that finishes the job on an already well-insulated property that is a band or two short of C, rather than the first thing to install on an unimproved one.

Common misunderstandings worth correcting

The most common misunderstanding we encounter is a homeowner expecting a straightforward one-for-one improvement simply because a heat pump is a low-carbon technology, without appreciating that RdSAP's headline rating is a cost model, not a carbon model. The second is assuming the assessor can simply see the outdoor unit and infer the specification; without an MCS certificate the assessor has no reliable data on the rated efficiency and cannot enter anything beyond a generic default, which understates the benefit. The third is installing a heat pump but leaving old, undersized radiators in place, which limits real-world performance and can be reflected in a lower recorded efficiency than the unit is technically capable of.