ESOS Phase 4 & Compressed Air Energy Efficiency
ESOS Phase 4 has a qualification date of 31 December 2026 and a compliance deadline of 5 December 2027. For qualifying organisations, measured compressed-air data can help identify and evidence practical energy-saving opportunities within the wider ESOS assessment.
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Qualification · 31 Dec 2026
Compliance · 5 Dec 2027
Action Plan · 5 Dec 2028
Measured System Data
ISO 11011 Audit Principles
ESOS Phase 4: The Current Position
The Environment Agency published dedicated Phase 4 guidance on 30 July 2026 following amendments to the ESOS Regulations. Some proposals discussed in earlier years were changed, postponed or removed, so older ESOS articles should not be relied on without checking the current rules.
| Phase 4 Milestone | Current Date |
|---|---|
| Phase 4 compliance period | 6 December 2023 to 5 December 2027 |
| Qualification date | 31 December 2026 |
| Notification of compliance deadline | 5 December 2027 |
| Action plan deadline | 5 December 2028 |
| Progress updates | Required in 2029 and 2030, with an additional third progress update due by 5 December 2031 under the 2026 changes. |
Who Qualifies for ESOS Phase 4?
An undertaking can qualify if, on the qualification date and subject to the detailed ESOS rules, it meets either of the following large-undertaking tests:
- It employs 250 or more people; or
- It has annual turnover in excess of £44 million and an annual balance-sheet total in excess of £38 million.
Corporate-group rules can bring additional UK undertakings into scope where a group contains a qualifying large undertaking. Organisations close to the thresholds can also need to review previous accounting periods because ESOS size status can depend on two consecutive accounting periods.
Qualification is an organisation-level question. A compressed-air supplier should not make the final legal determination for the participant or group.
What Changed for Phase 4?
DEC & Green Deal Routes RemovedDisplay Energy Certificates and Green Deal Assessments are no longer Phase 4 compliance routes.
Energy Savings ReportingPhase 4 reporting includes details of measures implemented and energy savings achieved during the compliance period.
Action Plan ReviewThe ESOS report must identify proposed measures that were not implemented and explain why.
Third Progress UpdateThe 2026 amendments introduced an additional progress update due by 5 December 2031.
ISO 50001 Route AdjustedParticipants complying solely through qualifying ISO 50001 certification can have reduced ESOS reporting and lead-assessor obligations.
No Blanket Net-Zero Audit MandateThe final Phase 4 rules should be followed rather than older consultation-era claims about mandatory net-zero planning.
Does ESOS Force Businesses to Implement Every Recommendation?
ESOS is an assessment, reporting and energy-saving scheme. Phase 4 increases accountability by requiring participants to report achieved savings and explain why proposed measures were not implemented, but that is different from saying every audit recommendation must automatically be carried out.
This distinction matters when evaluating compressed-air projects: recommendations should be supported by measured demand, expected savings, operational risk, capital cost and realistic payback.
Where Compressed Air Fits Into ESOS
Compressed air can be a significant industrial energy user, particularly on manufacturing sites with multiple compressors, long operating hours, leaks, high pressure or unstable demand.
For an ESOS participant, compressed-air energy analysis can help support the assessment of significant energy consumption and identify quantified improvement opportunities.
But a compressed-air audit is not the whole ESOS assessment. The organisation remains responsible for its wider ESOS obligations across buildings, industrial processes, transport and other energy uses that fall within scope.
How Compressed Air Systems UK Audits a System
Compressed Air Systems UK provides compressed-air energy-saving audits structured around recognised ISO 11011 audit principles and measured site data.
| Stage | What We Review | Why It Helps |
|---|---|---|
| System Review | Compressors, layout, pipework, pressure and points of use. | Establishes how the system is configured and where inefficiency may occur. |
| Data Logging | Live operating data over a representative period; Tanair currently uses a minimum 14-day logging period for its energy-saving audit service. | Captures demand variation rather than relying on nameplate assumptions. |
| Pressure & Flow | System pressure, flow and operating behaviour. | Shows whether pressure is excessive, unstable or restricted. |
| Electrical Data | Power use, current, voltage and operating hours where measured. | Supports a more defensible running-cost assessment. |
| Leak & Misuse Review | Leaks, inappropriate air use and avoidable demand. | Highlights opportunities that may not require compressor replacement. |
| ROI Reporting | Savings opportunities, priorities and indicative payback. | Helps businesses compare improvement options commercially. |
Can a CAS Energy Audit Make You ESOS Compliant?
Not on its own. A compressed-air audit can provide useful measured data, analysis and recommendations for the compressed-air element of an ESOS assessment, but it does not replace the participant’s full ESOS assessment, reporting, sign-off or notification obligations.
Where a lead assessor is required by the chosen ESOS compliance route, that role must be fulfilled in accordance with the ESOS rules. Organisations should coordinate specialist compressed-air evidence with their ESOS lead assessor or compliance team.
Typical Compressed-Air Opportunities an Audit Can Identify
Air LeakageLeaks can create avoidable compressor run time and increase system demand.
Excessive PressureRunning above the real point-of-use requirement can increase energy use and leakage losses.
Poor ControlMultiple compressors or badly configured load/unload controls can cause unnecessary running.
Incorrect SizingAn oversized or undersized compressor can create poor control, pressure problems or wasted energy.
Pipework LossesRestrictions, small-bore pipe and long routes can cause avoidable pressure drop.
Variable DemandMeasured load profiles can show whether VSD control is likely to suit the site.
VSD Compressors: Use Audit Data Before Recommending One
VSD can be highly useful where demand genuinely varies, but it is not automatically the best answer for every ESOS participant or compressed-air system.
VSD Can Make Sense When
- Demand changes materially during production.
- The existing fixed-speed compressor spends substantial time unloaded.
- Pressure can be controlled more effectively with variable output.
- The machine is correctly sized across minimum and peak demand.
Fixed Speed Can Still Be Right When
- Demand is consistently high and stable.
- The compressor operates efficiently as a base-load machine.
- Annual operating hours or economics do not support a VSD upgrade.
- A separate VSD machine already trims variable demand.
Current Energy-Efficient Compressor Routes
The product routes below provide useful current compressor options without hard-coding prices, so availability and pricing remain on the individual product pages.
PhaZair 230V 5.5 kW VSD27.5 CFM, 8 bar, single-phase variable-speed rotary screw compressor.View product →
Power Systems G-TEC 1108-270 DF DVReceiver-mounted variable-speed full-feature compressor with dryer and filtration.View product →
Power Systems NOBEL 7.508-270 DV-DFReceiver-mounted VSD package with dryer and filters.View product →
Fini PLUS 2208 VSVariable-speed floor-mounted screw compressor for suitable industrial demand.View product →
Power Systems NOBEL 7.508 DVFloor-mounted VSD compressor from the NOBEL range.View product →
Tanair PM VSD RangeDirect-drive permanent-magnet VSD compressors for suitable variable-demand applications.View Tanair VSD →
Use ROI Carefully
Projected energy and carbon savings should be based on measured system data wherever possible. Online calculators are useful for early screening, but they should not be treated as guaranteed ESOS savings or investment returns.
Energy Saving AuditsISO 11011-style compressed-air system auditing with measured data.Explore audits →
Energy Savings ROI CalculatorEstimate potential operating-cost savings before detailed analysis.Open calculator →
Official ESOS Phase 4 GuidanceEnvironment Agency qualification, compliance and notification guidance.View GOV.UK guidance →
Phase 4 Checklist for Compressed-Air Users
- Confirm whether the organisation qualifies on 31 December 2026.
- Identify the ESOS responsible undertaking and group structure.
- Calculate total energy consumption and significant energy consumption.
- Coordinate the compressed-air assessment with the ESOS compliance route.
- Use measured compressor data where available.
- Record energy-saving opportunities and estimated savings.
- Track measures implemented during the compliance period.
- Keep evidence needed for the ESOS report, notification and action-plan review.
ESOS Phase 4 & Compressed Air FAQs
What is the ESOS Phase 4 compliance deadline?
The Phase 4 notification of compliance deadline is 5 December 2027.
What is the Phase 4 qualification date?
The qualification date is 31 December 2026.
What are the Phase 4 size thresholds?
Subject to the detailed ESOS rules, a large undertaking meets the employee test at 250 or more employees, or the financial test where annual turnover exceeds £44 million and annual balance-sheet total exceeds £38 million.
Is Net Zero planning a mandatory Phase 4 ESOS requirement?
The current 2026 Phase 4 guidance should be followed for net-zero and reporting requirements. Consultation-era proposals should not be treated as current legal requirements unless they appear in the final amended ESOS rules.
Does ESOS require every recommendation to be implemented?
No blanket requirement forces every recommendation to be implemented. Phase 4 does, however, require reporting on achieved savings and an action-plan review explaining proposed measures that were not implemented.
Can a compressed-air energy audit support ESOS?
Yes. It can provide measured data and recommendations for the compressed-air element of the wider ESOS assessment.
Does a CAS compressed-air audit make us ESOS compliant?
No. It supports the compressed-air element only. The participant remains responsible for the full ESOS assessment, reporting, sign-off and notification requirements.
Does VSD always save energy?
No. VSD is most beneficial where demand varies materially and the compressor is correctly sized. Stable high demand can favour fixed-speed capacity.
How long does your compressed-air data logging run?
The current Tanair energy-saving audit service states a minimum 14-day logging period to capture representative changes in demand.
Preparing for ESOS Phase 4?
If compressed air is a significant part of your site’s energy use, measured system data can help identify credible efficiency opportunities before the 5 December 2027 compliance deadline.
Request an Energy Saving Audit
Call 0121 753 3330
Compressed Air Systems UK · Unit 15, Fortnum Close, Birmingham, B33 0LG
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