Study finds UK Energy Performance Certificates do not match measured household CO2 emissions

A study that compared Energy Performance Certificate (EPC) ratings with actual meter readings from 1,038 homes found little difference in measured carbon emissions between properties with high and low EPC ratings, calling into question the certificates' reliability as a guide to household energy performance.

The trial, led by Atom Bank, compared estimated CO2 emissions derived from EPC ratings with primary energy use measured directly from meter data and reported minimal variation in emissions across EPC bands. Properties rated in bands A to C, usually regarded as the most energy efficient, did not show significantly lower measured emissions than those in bands D to G, the study said. Energy Performance Certificates are required when a home is sold or let in the UK and rate buildings on a scale from A (most efficient) to G (least efficient).

The findings have prompted calls from Atom Bank and data partners for the government, energy suppliers and the financial sector to work together to reform EPCs and move from theoretical estimates to actual energy performance data, such as utility bills or smart-meter readings. Edward Twiddy, director of ESG at Atom, said the trial shows EPC ratings "do not reliably reflect actual household emissions" and described inaccurate data as a barrier to reaching net zero.

Researchers at University College London’s Energy Institute reported a similar pattern when examining a larger national dataset, finding little variation in primary energy use above EPC band C even after adjusting for household size and thermostat temperature. The UCL team is working to identify the causes of the discrepancies as part of a government study into EPC accuracy that has not yet been published.

Industry voices described practical problems with current assessment practices. Gareth Jones, a solar expert and president of the Federation of Master Builders in Wales, said EPC assessments "have not kept up with modern technology and changes across the sector" and warned of a "massive problem with rogue assessors drawing up bogus EPC reports and getting away with it." He said some assessors base reports on assumptions about insulation rather than physical checks and called for tougher penalties when assessments are found to be incorrect.

Scott Harrison, director of strategy and innovation for business information at Experian, said collaborating in the trial reinforced the view that EPCs are "not a sufficiently accurate way of measuring household carbon emissions" and underlined the need to shift to real-world data.

The accuracy of EPCs carries regulatory and financial consequences. Landlords must currently meet a minimum EPC rating of E to let homes, unless exempt, and the government has been considering raising that threshold to C by 2030 for private rentals, a change that could affect landlords and holiday-let operators. EPCs also influence access to some mortgage products, eligibility for finance and perceptions of a property's running costs and value.

Atom Bank urged faster implementation of proposed reforms that would incorporate measured energy performance and strengthen assessments of build quality to ensure homes meet claimed efficiency standards. The bank said the trial's findings have implications for green lending, banks' carbon reporting and policy efforts to reduce residential emissions while addressing social issues such as fuel poverty.

UCL researchers continue to analyse why measured energy use appears similar across a range of EPC bands and are contributing to the government's ongoing review of the certification process. Policymakers face the challenge of balancing improved data collection and enforcement against costs and practicalities for homeowners, landlords and the construction and assessment industries.

The study and subsequent calls for reform add to growing scrutiny of the methods used to estimate household energy use and the governance of the EPC system as the UK seeks more accurate tools to target emissions reductions and support consumers through the transition to cleaner energy sources.