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Last updated October 2026.
An ESOS audit is not a walk-round
Plenty of businesses have had an energy survey: someone walks the building, notes the old lighting and the boiler nameplate, and sends a report with a list of suggestions. An ESOS energy audit is a defined thing with a standard behind it, and a lead assessor cannot sign off a survey that does not meet it.
The audit must be based on measured consumption data covering the reference period, analyse how and where that energy is used, identify savings opportunities and, for each, assess the costs and benefits over the life of the measure. It must cover the significant areas of consumption it is being used for, which in practice means site visits to a representative sample of the organisation’s buildings, processes and transport. The report has to be in a form the organisation could act on.
What a compliant audit covers
| Component | What the assessor needs |
|---|---|
| Consumption data | Metered or billed data for the reference period, by site and fuel. Half-hourly electricity data where available. Transport fuel from fuel cards, expenses or mileage records. |
| Energy profile | Where the energy goes: lighting, heating, cooling, process, IT, transport. Benchmarks against similar sites where useful. |
| Site visits | A representative sample of sites, chosen to reflect the range of buildings and activities. Every site need not be visited; the sample must be justified. |
| Savings opportunities | Specific measures with estimated energy and cost savings, capital cost and payback or life-cycle cost analysis, not generic suggestions. |
| Report | Findings and recommendations presented so the organisation can decide and act; the basis for the action plan. |
The lead assessor does not necessarily carry out the audit. Internal staff or other consultants can do the work, with the assessor reviewing it against the standard and confirming it is adequate. That is often the economical route for organisations with in-house facilities or engineering teams.
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Send us a recent bill or a quick description of your sites and we will tell you plainly what applies to you and what it would involve. No obligation.
Alternative compliance routes
Not every kilowatt-hour has to be audited. Energy covered by a certified ISO 50001 energy management system is compliant without a separate ESOS audit, and so is energy covered by a valid Display Energy Certificate with recommendation report or a Green Deal Assessment. Organisations commonly mix routes: ISO 50001 for the main factories, audits for offices and transport.
Whichever routes are used, at least 95 percent of total consumption must be covered, and the lead assessor confirms the whole picture. The residual 5 percent is the place for tiny sites and uses that are not worth the cost of measuring precisely.
Frequently asked questions
Who can carry out an ESOS energy audit?
Anyone competent, including internal staff, provided a registered lead assessor reviews the work and confirms it meets the standard. Many organisations have the assessor do the audit as well.
Does every site have to be visited for ESOS?
No. A representative sample is acceptable, chosen and justified to reflect the range of sites and activities. Very large estates sample; small ones usually visit everything.
What is a lead assessor?
An individual on one of the approved ESOS registers, qualified to review and sign off assessments. They must be registered at the time of sign-off.
Does an ESOS audit have to include transport?
Transport energy, including company vehicles and business travel in employees’ own cars, is part of total consumption and must be measured. It can be audited or placed in the unaudited 5 percent if small.
How is an ESOS audit different from an energy survey?
An ESOS audit must analyse measured consumption data, cover significant areas of use with justified site sampling, and include life-cycle cost analysis of specific savings measures. A general survey does not have to do any of those.
Can ISO 50001 replace an ESOS audit?
For the energy it covers, yes. An organisation whose certified system covers all its consumption can comply through ISO 50001 alone: no lead assessor is needed, though it must still notify the Environment Agency and have a director sign off.
Need help? Get in touch
Call us on 020 8036 5715, or email us, and we will take it from there.