ESOS energy audits · Part 4 Chapter 3
The ESOS energy audit: what the Regulations make it do
An ESOS energy audit is the audit that regulations 26 and 27 of the ESOS Regulations 2014 require: of at least 95% of a participant’s energy, on verifiable data, with site visits.
It must price each saving it finds, in pounds and in kWh, and give a payback period and an implementation programme.
Since 22 July 2026 it is one of only two Phase 4 routes, and its report now also records the savings already achieved.
Definitions
Three quantities, one audit
ESOS counts energy three times, and the audit comes last.
First the participant calculates its total energy consumption, then it may identify its significant consumption, and then it audits that significant part, or the total if it skipped the second step.
Regulation 26(2) lets it split the work into two or more audits, each on a different area, each on its own 12 months of data.
Energy covered by an ISO 50001 system is taken out of the audit’s scope, and the rest is audited.
On legislation.gov.uk regulation 26(1) still opens “Subject to Part 6”, though SI 2026/701 regulation 12 changed it to “Subject to regulations 33(3) and 33A”; read the two together.
| Term | Meaning | Provision |
|---|---|---|
| Total energy consumption | All energy supplied to and consumed by the participant, over the reference period | reg 22 |
| Significant energy consumption | Areas making up not less than 95% of the total, if the participant chooses to identify them | reg 25 |
| Energy audit | An audit of the significant (or total) consumption under Part 4 Chapter 3 | reg 2(1) |
Coverage
The 95% line, and the 5% you choose
Regulation 25(2) defines significant consumption as assets and activities that together account for not less than 95% of the total.
The 95% is a floor, and it may be measured in energy units or by energy spend, an option the Environment Agency’s guidance does not mention.
The line was 90% until SI 2023/1182 raised it for Phase 3, so the 95% is not a Phase 4 change.
The participant chooses the up to 5% it leaves out, and the guidance suggests keeping the largest consumers in.
Identifying significant consumption is optional: a participant that does not do it must cover all of its energy.
By group member, by site, by asset or activity, or by fuel — or a mix.
Whatever is excluded is recorded in the evidence pack.
What counts
Buildings, transport, processes and everything else
ESOS counts energy supplied to and consumed by the participant in the UK, including the offshore area.
Regulation 2(1) splits it into four organisational purposes; the Environment Agency’s guidance decides most of the edge cases.
| Include | Exclude |
|---|---|
| Electricity, gas, heating fuels, renewables and transport fuel supplied to you | Energy you pass on to a third party unconsumed |
| Energy you generate yourself | Surplus industrial heat you capture and reuse |
| For CHP: the incoming fuel and mains electricity | The heat and electricity the CHP makes |
| Company cars, fleet you operate, personal or hire cars — on business use | Train travel, flights and taxis you do not operate |
| Aircraft and vessels you operate, on journeys starting or ending in the UK | Goods transport you subcontract |
| Buildings where you are supplied with, and consume, the energy | Employees’ energy at home |
| Construction plant and generators held on both key dates | Energy consumed outside the UK and offshore area |
The four organisational purposes are transport, industrial processes, buildings, and any other purpose, and the fourth is where the awkward energy lands.
The transport test is who is supplied with the fuel for business use; the guidance draws no distinction between company cars and pool cars.
Between landlord and tenant, the energy belongs to whoever is supplied with it and consumes it, and the one who can control it should take it.
The whole list is in sections 4.2 to 4.3.6 of the Environment Agency’s Phase 4 guidance, which is a restatement the Regulations outrank.
The data
Two windows of data, not one
ESOS uses two different 12-month windows, and most confusion about “the reference period” comes from running them together.
The reference period is for the total energy calculation, and it sits around the qualification date.
The audit data window is for the audit itself, and can reach back to 6 December 2022, but never more than 24 months before the audit starts.
So an audit begun late in 2027 cannot use 2022 data: the 24-month limb closes first.
Regulation 26(5) forbids using the same data for audits in more than one compliance period, so Phase 3’s audit data cannot be recycled.
Where 12 months of verifiable data does not exist, regulation 26(7) allows a shorter period of verifiable data, or a reasonable estimate.
Since 22 July 2026 every estimate must be accompanied by the data used to make it, and the methods and data go in the evidence pack.
The guidance says the reference period should include the qualification date and end “before” the compliance date; regulation 22(5) says “on or before”, and governs.
| Window | Phase 4 rule | Provision |
|---|---|---|
| Reference period (total consumption) | 12 months, beginning no more than 12 months before 31 Dec 2026, ending on or before 5 Dec 2027 | reg 22(5) |
| Audit data | 12 months, beginning no earlier than 6 Dec 2022 and no more than 24 months before the audit starts, ending on or before 5 Dec 2027 | reg 26(4)(b) |
The content
What an ESOS audit must contain, item by item
Regulation 27(1) sets the content, each limb qualified by “so far as reasonably practicable”.
Limbs (d) and (e) were rewritten for Phase 3 and apply unchanged in Phase 4.
| Reg 27 | The audit must |
|---|---|
| (1)(a) | Analyse energy consumption and energy efficiency, where practicable on energy consumption profiles |
| (1)(b) | Identify any way the participant can improve its energy efficiency |
| (1)(c) | Recommend the measures that are reasonably practicable and cost effective — the “energy saving opportunities” |
| (1)(d)(i)–(ii) | For each opportunity: its organisational purpose and energy saving category |
| (1)(d)(iii) | Implementation considerations, including private rented property duties and available public grants |
| (1)(d)(iv)–(v) | Costs and benefits in pounds, and non-financial costs and benefits |
| (1)(d)(vi)–(vii) | Annual reduction in energy spend and energy consumption, and the payback period |
| (1)(e) | A recommended implementation programme: timescale, costs and benefits, payback |
Cost effectiveness is judged on the estimated energy saving against the estimated cost of the measure (regulation 27(4)).
Wherever practicable the cost must be a whole-life analysis: purchase, installation, maintenance and depreciation (regulation 27(5)).
Payback has a statutory definition: the estimated cost divided by the estimated annual reduction in energy costs, in years (regulation 27(7)).
The six energy saving categories are defined in regulation 2(1): management practice, behaviour change, training, controls, capital investment, and other.
An audit that does not use energy consumption profiles must say so to the scheme administrator and record the alternative method (regulation 27(6)).
The evidence
Site visits and the audit record
SI 2023/1182 added a duty to visit sites, from 29 November 2023, and a duty to record the audit in a fixed shape.
The visits must be to sites the responsible undertaking considers representative of how energy is used across the participant during the audit’s 12 months.
The record must justify that choice, which is where a sampling approach succeeds or fails on enquiry.
The government’s second post-implementation review lists justifying the site-sampling method among the Phase 3 changes.
| Reg 26(9) | The audit record must show |
|---|---|
| (a) | When the audit was carried out |
| (b) | The 12-month period it relates to |
| (c) | The consumption it covered |
| (d)–(e) | How many sites there are, and how many were visited |
| (f) | Why the sites visited are representative |
| (g) | Where less than 12 months’ data was used, how much and why |
Ratios
Energy intensity ratios, one per purpose
Every participant, whatever its route, calculates an energy intensity ratio for each organisational purpose it used energy for, under regulation 25C.
A ratio divides the kWh for that purpose by an indicator of activity, such as floor area for buildings.
The indicators are not prescribed, and the guidance advises against turnover, which moves for reasons that have nothing to do with energy.
The ratios chosen in Phase 3 are meant to be the baseline, and a participant that changes them is asked to explain why in its notification.
SECR asks for a single ratio of the company’s choosing, so the two duties are not interchangeable.
Who oversees it
The lead assessor, and the new personal duty
Regulation 21 requires a lead assessor from an approved register, and the GOV.UK ESOS overview lists seven registers.
The competence standard behind them is PAS 51215:2014, fixed by regulation 12; a register such as CIBSE Certification’s is a subset of the body’s wider membership.
The guidance puts the duty to check an assessor’s accreditation on the participant.
No lead assessor is needed where total consumption is less than 40,000 kWh, a limb inserted for Phase 3, or where ISO 50001 covers the energy, or where consumption is zero.
New in Phase 4, the lead assessor must personally notify its approval body within seven days of the assessment being completed, naming at least two contacts, one of them the responsible officer.
Whether the assessor is independent of the participant decides whether one responsible officer signs or two.
Questions to ask before appointing one are set out by the sister site in its ESOS consultant checklist.
Association of Energy Engineers · CIBSE · Elmhurst Energy Systems · Energy Institute · Energy Managers Association · Institute of Sustainability and Environmental Professionals · Quidos.
After the audit
The ESOS report, and what Phase 4 adds to it
The audit feeds the ESOS report, which the responsible officer confirms before the participant notifies by 5 December 2027.
SI 2026/701 added two things to the report: the energy savings achieved in the compliance period, measure by measure in kWh, and a review of the last action plan’s unimplemented measures.
Only the combined savings figure is published; the review is not.
The action plan comes a year later, by 5 December 2028, and regulation 28 of SI 2026/701 gives it three progress updates.
The plan is on the ESOS action plan, the Phase 4 changes on ESOS Phase 3 vs Phase 4, and the audit’s place in the whole on ESOS Phase 4 requirements.
Routes
The routes that closed, and what failing the audit costs
Display Energy Certificates and Green Deal assessments stopped being ESOS routes on 22 July 2026, when regulation 26 of SI 2026/701 omitted regulation 34 of the 2014 Regulations.
The Environment Agency’s reason is that they give more limited and less tailored recommendations than an ESOS audit.
Their data can still inform an intensity ratio or a past-savings estimate; it cannot replace the audit.
Failing to undertake the ESOS assessment is penalised under regulation 45 at up to £50,000 plus £500 per working day for up to 80 working days, set out on ESOS penalties.
The Phase 4 guidance is the Environment Agency’s; the policy behind it is the Department for Energy Security and Net Zero’s.
Frequently asked
ESOS energy audits: questions people ask
What must an ESOS energy audit cover?
Either the participant's areas of significant energy consumption — assets and activities making up not less than 95% of total energy consumption — or, if the participant chose not to identify them, its total energy consumption (regulation 26(1)).
Energy for transport, industrial processes, buildings and any other purpose is all in scope.
What must an ESOS energy audit contain?
Regulation 27 requires, so far as reasonably practicable, an analysis of energy consumption and efficiency, the ways efficiency could improve, and recommendations of cost-effective measures.
For each opportunity: its organisational purpose and energy saving category, implementation considerations, costs and benefits in pounds, non-financial costs and benefits, the annual reduction in energy spend and consumption, and the payback period. It must also recommend an implementation programme with a timescale.
What data period can an ESOS Phase 4 audit use?
Verifiable data over 12 consecutive months that begin no more than 12 months before the start of the compliance period — so no earlier than 6 December 2022 for Phase 4 — and no more than 24 months before the audit begins, and that end on or before 5 December 2027 (regulation 26(4)).
No data may be used for audits in more than one compliance period.
Is there an ESOS energy audit template?
No statutory template exists.
The Regulations prescribe what the audit must do and record (regulations 26 and 27) and what the notification must report (Schedule 3); how the audit report is laid out is left to the participant and its lead assessor.
Who can carry out an ESOS energy audit?
The audit is overseen by a lead assessor appointed under regulation 21, who must be on one of the approved registers — seven are listed by the Environment Agency.
The competence standard is PAS 51215:2014.
No lead assessor is needed where total consumption is under 40,000 kWh, where ISO 50001 covers the energy, or where consumption is zero.
Do ESOS audits need site visits?
Yes.
Regulation 26(3A), in force since 29 November 2023, requires visits to sites the responsible undertaking considers representative of how energy is used across the participant, and regulation 26(9) requires a record of how many sites exist, how many were visited, and why they are representative.
Which transport fuel belongs in an ESOS audit?
The Environment Agency's guidance includes fuel you are supplied with for business use: company cars, fleet vehicles you operate, personal or hire cars on business use, and aircraft, trains or ships you operate.
It excludes train travel, flights and taxis you do not operate, and goods transport you subcontract.
Sources
Primary sources
Every figure, date and status on this page traces to the instrument’s owner.
Secondary commentary is never the source for a number.
- legislation.gov.ukESOS Regulations 2014, Part 4 Chapter 3 (regulations 26–27) — the energy audit
Audit data window (reg 26(4)), site visits (26(3A)), audit records (26(9)) and what an audit must identify and estimate (reg 27).
- legislation.gov.ukESOS Regulations 2014, regulation 22 — total energy consumption and the reference period
Reference period begins no more than 12 months before the qualification date and ends on or before the compliance date (reg 22(5)).
- legislation.gov.ukESOS Regulations 2014, regulation 25 — areas of significant energy consumption
Not less than 95% of total consumption, by energy units or by energy spend; identification is elective.
- legislation.gov.ukESOS Regulations 2014, regulation 25C — energy intensity ratios
A ratio for each organisational purpose; the four purposes are defined in reg 2(1).
- legislation.gov.ukESOS Regulations 2014, regulation 21 — the lead assessor
Reg 21(3): no appointment below 40,000 kWh; reg 21(2A): the seven-day notification (SI 2026/701 reg 8).
- legislation.gov.ukESOS Regulations 2014, regulation 12 — approved registers and PAS 51215:2014
The approved-register mechanism; the competence standard PAS 51215:2014.
- legislation.gov.ukESOS Regulations 2014, regulation 2 — interpretation
“Energy audit”, “organisational purpose”, “energy saving category”.
- legislation.gov.ukThe Energy Savings Opportunity Scheme Regulations 2014 (SI 2014/1643), revised text
In force 17 July 2014. Consolidation of the 2026 amendments is partial — read with SI 2026/701.
- legislation.gov.ukThe Energy Savings Opportunity Scheme (Amendment) Regulations 2023 (SI 2023/1182)
Inserted site visits (reg 26(3A)), audit records (26(9)) and the full reg 27(1)(d)–(e) content, from 29 November 2023.
- legislation.gov.ukThe Energy Savings Opportunity Scheme (Amendment) Regulations 2026 (SI 2026/701)
Made 23 June 2026, in force 22 July 2026: the Phase 4 changes. Made under Energy Act 2023 ss.254–260 and 263.
- legislation.gov.ukSI 2026/701, regulation 28 — the third progress update (new reg 34B(1)(c))
- Environment AgencyHow to comply with the Energy Savings Opportunity Scheme (ESOS) phase 4
Published 30 July 2026. A restatement of the Regulations, never the source over them; where it and the SI differ, the SI governs.
- Environment AgencyComply with the Energy Savings Opportunity Scheme (ESOS) phase 4 — publication page
- Environment Agency / GOV.UKEnergy savings opportunity scheme (ESOS): find out if you qualify and how to comply
Rewritten for Phase 4 on 2 September 2026; seven approved lead assessor registers; PAS 51215-1 and -2:2025 voluntary.
- CIBSE CertificationESOS lead assessor register
One of the seven approved registers; its own page for its own scheme.
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