EPC rating discrepancies: what they mean for your bills and your mortgage

What to read on the certificate

• Inspection and lodgement dates. An EPC is valid for ten years. A certificate lodged before an extension, a new boiler or a re-roof describes a property that no longer exists.
• Current and potential rating and score. The gap between them is the assessor's view of headroom, and the recommendations list what it assumes.
• Total floor area. Cross-check against the listing — see square footage versus floor plan claims.
• Main heat, main fuel and controls. Storage heaters, oil, LPG and electric boilers all carry very different running costs from mains gas.
• Walls, roof, windows, floor descriptions and their efficiency ratings. "Solid brick, as built, no insulation" is the single most expensive line an EPC can contain.
• Estimated energy costs and CO₂. Modelled for a standard occupancy pattern, not for your household. Treat them as comparative, not predictive.

Common discrepancies

1. The listing quotes a rating better than the current certificate — often the potential rating quoted as if it were current.
2. The certificate is for a different flat in the same building. In converted blocks this is very common, and floor area and heating detail will not transfer.
3. The certificate describes single glazing or no loft insulation while the photographs show otherwise, meaning the work postdates the assessment and the rating understates the property.
4. No certificate is on the register at all. Some exemptions exist — listed buildings in certain circumstances, for example — but absence is worth a question.

What a poor rating costs

Two things: running costs, and remediation. Running costs you can estimate from the certificate's own modelled figures, adjusted for the current Ofgem price cap. Remediation you price from the recommendations — the certificate lists indicative costs and typical savings for each measure.

For most buyers the mortgage impact is indirect. Some lenders offer green mortgage products or better rates for higher-rated homes, and affordability assessments can take energy costs into account. Rules for rented property are set separately and change; if you are buying to let, check the current minimum energy efficiency standard requirements on GOV.UK rather than relying on older summaries.

Where remediation is genuinely needed — a solid-wall property with no insulation and an old boiler — quantified improvement costs are one of the strongest evidence-based negotiation points there is, because they are a cost you will actually incur.