ESOS Phase 4 audits built on 12 months of metered data
ESOS is the UK energy audit scheme for large undertakings, run by the Environment Agency. Aqueduct meters consumption by site and end use, so the lead assessor works from measured figures rather than bills and estimates.
Who has to comply
An undertaking qualifies if it employs 250 or more people, or has annual turnover over £44 million and a balance sheet over £38 million, on the qualification date. Its UK corporate group comes in with it. The Phase 4 qualification date is 31 December 2026.
A lead assessor signs off the audit and a board-level director confirms it, unless total energy use is under 40,000 kWh or fully covered by a valid ISO 50001 certificate. Display Energy Certificates no longer count as a route from Phase 4.
What Phase 4 requires, and the data behind each duty
Regulation numbers refer to the ESOS Regulations 2014 as amended in 2026.
| Requirement | What it asks for | Data Aqueduct supplies |
|---|---|---|
| Reg 22, total energy consumption | All energy used in buildings, industrial processes and transport. | Electricity, gas and fuel meters per site, summed into one group total in kWh. |
| Reg 25, significant energy consumption | Areas that account for at least 95 percent of total consumption. | Sub-meter totals by building, plant and end use, ranked so the 95 percent line is visible. |
| Reg 25C, energy intensity ratios | Ratios for buildings, transport and processes, from verifiable data where practicable. | kWh per square meter or per unit of output, calculated from metered data. |
| Reg 26, energy audit | An audit based on verifiable consumption measured over a 12 month period. | Interval data for the chosen 12 months, with gaps and estimates flagged. |
| Reg 27D and 27E, progress since last phase | Savings made against the previous action plan, with any shortfall explained. | Before and after consumption per measure, normalized for weather. |
Dates and penalties
Phase 3 action plan progress update due, signed by a board-level director.
Source: GOV.UK ESOS guidancePhase 4 notification of compliance deadline.
Source: GOV.UK ESOS guidanceMaximum penalty for failing to carry out an audit, plus up to £500 a working day for up to 80 days.
Source: ESOS Regulations, reg 45sites in 21 countries run on Aqueduct.
and 9 clinics in one of India’s top hospital chains.
US airport running water intelligence on Aqueduct.
of commercial real estate under Aqueduct.
FMCG manufacturing campus.
operations run on Aqueduct.
Related
Common questions
The regulations ask for verifiable data where reasonably practicable. Estimates are allowed where measurement is not practicable, but the assessor must be able to see how each figure was reached, which is why metered sub-loads help.
It can, if the certificate covers all of your energy use, was issued after 5 December 2023 and is still valid on 5 December 2027. Partial coverage means the rest still needs an ESOS audit.
For Phase 4 the period can start no earlier than 6 December 2022. Choose a recent, typical year; Aqueduct exports any 12 month window from its interval history, with gaps and estimated days marked for the lead assessor.
Not by name. Splitting use between buildings, processes and transport is hard from whole-site bills alone, so sub-meters on the largest loads give the lead assessor figures that can be checked. See load disaggregation.
See Aqueduct on your own facility.
Bring a site, a utility bill or a question. We will show you where the loss is.