The ESOS energy audit: what it must cover, and what it must contain

What it is

An audit in the energy sense, not the accounting one

The guidance defines the ESOS energy audit as an assessment of the participant’s energy consumption and energy efficiency to identify tailored and cost-effective measures it could implement to save energy.

It is not a financial audit and not an assurance engagement: nobody gives an opinion on reported figures, and ESOS sets no target the audit has to meet.

The audit is one part of the wider ESOS assessment, which also measures total consumption, calculates intensity ratios and ends in a notification; the ESOS assessment page sets out the whole.

Where an ISO 50001 certificate covers consumption, that consumption need not be audited, and where a certificate covers all of the total or significant consumption no audit is needed at all.

Since 22 July 2026 those are the only two routes: Display Energy Certificates and Green Deal Assessments were removed by SI 2026/701.

Site visits

Representative sites, and the reasons for choosing them

The sites visited must be those the responsible undertaking considers representative of how energy is used across the assets and activities the audit covers.

There is no prescribed sampling method, and the guidance suggests agreeing the approach with the lead assessor.

Participants with many identical or very similar sites would be expected to need fewer visits for the sample to be representative.

The visits do not reduce the data duty: consumption data is collected and analysed for every area of significant consumption, however few sites are visited.

In a compliance audit, the guidance says, the regulator looks for well-reasoned, documented justifications for the sampling and for why conclusions from the visited sites apply to the others.

In a multi-tenanted building one visit and audit can serve several participants by agreement, each still responsible for its own compliance and its own opportunities.

Methods and standards

ISO 50002, BS EN 16247, or your own method

ESOS does not mandate an audit methodology, the guidance says, and Appendix C points to ISO 50002 and BS EN 16247, published through the BSI catalogue, as possible ones.

ISO now lists ISO 50002:2014 as withdrawn, with ISO 50002-1:2025 as the new version; neither is required by ESOS, so the change affects method, not compliance.

An in-house method is acceptable if it meets the ESOS minimum requirements, and ISO 14001-certified organisations can run ESOS-standard audits within their internal audit programme.

Audits done for other purposes can count, if they meet the minimum requirements, fall in the compliance period and were not relied on in a previous one; Appendix C applies that to Climate Change Agreement audits reviewed by a lead assessor.

Audit work need not happen at once: Appendix C lets it be spread across the period, provided it is finished by the compliance date.

Where units need converting into kWh, the guidance points to the fuel properties tab of the government conversion factors.

What it is not

Neighbouring exercises that are not an ESOS audit

A Display Energy Certificate rates a building’s operational energy use; it was an ESOS route in earlier phases and is not one now.

An SECR disclosure reports energy and emissions every year in the annual report, a disclosure duty rather than an audit; the SECR reporting guide covers it.

Sustainability assurance gives an opinion on reported information, a different exercise again, set out on sustainability assurance.

Where ESOS data feeds wider reporting, the overlap is mapped on ESOS and UK SRS integration, and the standards themselves on UK SRS S1 and S2; the wider reporting picture starts on the uksrs.org.uk home page.

The instrument is SI 2014/1643 as amended; the Phase 3 audit rules are in the Phase 3 guidance and the regulator is the Environment Agency in England.