Updated for ESOS Phase 4 · 2026 Guidance
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.
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.
Read our Latest Reviews
bryan wright
10 months ago
I have used Compressed Air Systems a number of times for repairs, servicing and also to purchase air compressors. The service I have received has been fantastic, friendly, helpful and very well priced. This company definitely offers convenience, value & quality. I massive thank you to all the team at Compressed Air Systems.
Response from the owner
Hi Bryan,Thank you so much for taking the time to review our company. We greatly appreciate your thoughtful comments and are thrilled to hear that you are satisfied with our services. It’s been a pleasure working with you, and we value the positive relationship we've built.We look forward to discussing any future opportunities or addressing any needs you might have. Please feel free to reach out whenever you’d like.Kind regards, TEAM CAS10 months ago
Jordan Hay
11 months ago
I had an excellent experience with Compressed Air Systems! Their team was knowledgeable, friendly, and quick to respond. They helped me find the right compressor for my shop and even walked me through the installation process. Everything has been running flawlessly since day one. Highly recommend them for anyone needing reliable air solutions and professional service!
Response from the owner
Hello Jordan,Thank you for taking the time to share your feedback about the service you received. We are absolutely thrilled to hear that you’re satisfied with your experience! Your satisfaction means a lot to us. We look forward to speaking with you soon!Best wishes, Team CAS10 months ago
Sam Cain
1 year ago
Exceptional service! The team went above and beyond to help fix our machine and get us back up and running in no time. Their expertise, dedication, and quick thinking made all the difference. Highly recommend!
Response from the owner
Hi Sam, Thank you for taking time to review our company. I'm so glad we were able to help! Kind regards Team CAS1 year ago
Richard Vinten
2 years ago
I can't recommend CAS UK enough.
We had a Clarke for a couple of years that we abused running it 12 hours a day. We found CAS UK when it needed a repair, and we were very impressed with how quickly they responded and came out to repair and service the machine.
Our business started to expand and we needed a large compressor with a proper airlines feeding our machines and work stations. The guys from CAS supplied the new compressor and worked flat out getting the machine and pipe working in.
They're a brilliant group of lads with a great work ethic and really easy to communicate with.
We'll 100% continue to use and recommend them.
We had a Clarke for a couple of years that we abused running it 12 hours a day. We found CAS UK when it needed a repair, and we were very impressed with how quickly they responded and came out to repair and service the machine.
Our business started to expand and we needed a large compressor with a proper airlines feeding our machines and work stations. The guys from CAS supplied the new compressor and worked flat out getting the machine and pipe working in.
They're a brilliant group of lads with a great work ethic and really easy to communicate with.
We'll 100% continue to use and recommend them.
Response from the owner
Hi Richard, thank you for taking the time to review our company and the service you received. It’s thrilling to read such positive feedback. We look forward to working with you again soon. Team CAS2 years ago
Mike H N Fisher
2 years ago
Excellent firm to deal with.
Very efficient at every level.
Quite a rare find ~ don't waste the opportunity if you have a need within their expertise. Mike Fisher
Very efficient at every level.
Quite a rare find ~ don't waste the opportunity if you have a need within their expertise. Mike Fisher
Response from the owner
Thank you for your kind words Mike it’s been a pleasure to partner with you. We look forward to speaking to you soon. Kind regards Team CAS2 years ago
LJD Tyres
2 years ago
Turned up this morning, no appointment or nothing, had what i needed in stock and had it fitted in less than 30 mins! sorted me right out getting me back on the road changing tyres! thanks once again cant recommend you enough! see you when i next need you
Response from the owner
Thank you for your kind review, it was a pleasure to assist you today. We look forward to seeing you again soon! Team CAS2 years ago
James Deeming
2 years ago
Can't thank this company enough for getting me back on the road today. From the initial phone call, trying to explain the problem not having a clue what part is called what, the girl who answered knew exactly what I needed. To then arriving 30 minutes later and 2 engineers came out to my van and fixed the problem in minutes. Absolutely brilliant service. Thankyou!!!
Response from the owner
Hi James, thank you for visiting us today. It was a pleasure to assist you. We look forward to seeing you again soon. Team CAS2 years ago
Sheikh Mudassar
3 years ago
Response from the owner
Thank you for your review. Have a great day! Kind regards Team CAS3 years ago
Midland Mobile Leisure Services Limited
3 years ago
Very professional help me out this morning immediately to get me back on the road supplied fittings and new compressor 🙏🙏🙏🙏🙏💪💪💪
Response from the owner
Hi Paul, thank you so much for taking the time to review the service you received. We really appreciate your kind words and glad we could help this morning. You’re welcome back anytime! Kind regards Team CAS3 years ago
Harry Draper
4 years ago
Brilliant service
Used them for years!
Thank you
H D
Used them for years!
Thank you
H D
Response from the owner
Hi Harry, thank you so much for taking the time to review our company. We really appreciate your business and look forward to dealing with you again soon. Kind regards TEAM CAS4 years ago
Lewwwyy
4 years ago
Response from the owner
Thank you for your kind and honest review. Team CAS4 years ago
Les Owen
4 years ago
Took in what I believed to be a beyond repair compressor. Received back, an as new machine, all physical damage repaired and connector fittings renewed to latest standard.
Compressor delivered to my premises in what was a great service by Compressed Air Systems UK. Thanks for a great experience
Compressor delivered to my premises in what was a great service by Compressed Air Systems UK. Thanks for a great experience
Jordan Li
4 years ago
I have used CAS for 15 years.
Never let me down!
Always been brilliant & came out the same day if there is ever an issue.
Thank you
Jordan
Never let me down!
Always been brilliant & came out the same day if there is ever an issue.
Thank you
Jordan
Aaron Courtney
5 years ago
Me and my company have been using compressed air systems for around 10 years!
Very professional always great advisor for the best machine for what we need, friendly office staff and most of all the knowledge from them is second to none.
Would recommend to anyone that needs advise or want to buy the right machine for them.
Plus the backup you get is the best.
Very professional always great advisor for the best machine for what we need, friendly office staff and most of all the knowledge from them is second to none.
Would recommend to anyone that needs advise or want to buy the right machine for them.
Plus the backup you get is the best.
Amelia Blackwell
8 years ago
What a refreshing team to have as competent suppliers for our leads and compressed air; not once have they given us poor service. They've saved our business; A Gilligan (Coatings) Ltd thousands of pounds per year with new high tech and efficient equipment. Their advice and service supplied over the last 15 year period has been extremely valuable, we would never consider another company for our compressed air services
2WheelsOnly LTD
8 years ago
Had a new compressor fitted a few months ago. Perfect service and amazing aftercare.
I was advised well and even advised towards a better value option saving us a chunk of money. Top quality honest service all round...... Thanks again.
I was advised well and even advised towards a better value option saving us a chunk of money. Top quality honest service all round...... Thanks again.
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