TM44 Air Conditioning Inspections: The 2026 UK Compliance Guide

If your London office, shop, restaurant or warehouse has air conditioning that totals more than 12kW of cooling output, you are legally required to commission a TM44 inspection at least every five years. Most building owners I meet have no idea this rule exists until a Trading Standards officer or a buyer's solicitor asks for the certificate.

By then it's awkward. Sometimes expensive.

This guide pulls together what the legislation actually says, what an inspector checks on the day, what it costs in 2026, and how to make sure your system passes without drama. I have carried out these inspections across the capital for years, so the practical bits are based on what we actually find on commercial roofs and ceiling voids, not a marketing brochure.

What is a TM44 inspection

A TM44 inspection is a legally required energy efficiency assessment of any air conditioning system in a non-domestic building with a combined cooling output above 12kW. The name comes from CIBSE Technical Memorandum 44, which is the methodology assessors must follow.

The inspection is not a service. It is not a refrigerant check. It is an independent energy audit that produces a report and a certificate lodged on the national non-domestic energy register. The point is to flag oversized, badly controlled or poorly maintained systems that are quietly burning through electricity.

It was introduced under the Energy Performance of Buildings Directive and is enforced through the Energy Performance of Buildings (England and Wales) Regulations 2012. Scotland and Northern Ireland have parallel rules under their own statutory instruments.

The legal trigger: when does the 12kW rule apply

This is where most people trip up. The 12kW threshold refers to the effective rated cooling output of the system, not the electrical input and not a single unit's capacity.

If a single tenant or building owner controls multiple units inside one building, they are aggregated together. Four 3.5kW wall splits in a small clinic add up to 14kW. That clinic needs a TM44 certificate. A retail unit with two 7kW cassettes and a 5kW back office split sits at 19kW. Same rule applies.

The aggregation rule is set out in the government's official guide to air conditioning inspections, which states that "one or more air conditioning units within a building controlled by a single person are considered to comprise a single air conditioning system."

What counts toward the 12kW figure:

• Wall-mounted and ceiling cassette splits
• VRF and VRV multi-split systems
• Ducted indoor units
• Rooftop packaged units and AHUs with cooling coils
• Chillers feeding fan coil units
• Close-control units in server rooms

What is excluded: comfort fans, evaporative coolers without a refrigeration cycle, and any process cooling that serves a manufacturing or industrial process rather than the building's occupants.

If you are sizing a new system or replacing an old one and want to understand the kW figures we are talking about, our breakdown of AC system installation costs in the UK walks through how systems are specified by output.

Who is responsible: landlord vs tenant

The legal duty falls on the person "in control" of the system. In practice, that is whoever can switch the kit on, off, and adjust it.

For a fully fitted office where the landlord owns the central VRF and the tenant just controls the temperature on a wall stat, the landlord is responsible. According to the gov.uk guidance, "occupiers of a building, where a central air conditioning system is under the control of the building owner or manager, would not be liable for a penalty charge."

For a shell-and-core lease where the tenant fits out their own splits or VRF, the tenant is responsible. They commissioned and control the kit, so the certificate is theirs to organise.

For a multi-let building with a shared chilled water system but tenant-installed FCUs, you usually end up with both parties needing certificates, one for the central plant and separate ones per tenancy. This is the situation we see most often in older Holborn and Shoreditch conversions.

If you are negotiating a new lease, get this written into the agreement on day one. Ambiguity here causes real problems at rent review and sale. Our guide to choosing a commercial AC company in London covers what to expect from a contractor on lease handovers.

The 5-year cycle and how it works

Inspections must take place at intervals not exceeding five years. The clock starts on the date of the first inspection certificate, not the date of installation.

For new systems, the first inspection is required within five years of being put into service. So if you commissioned a new VRF in March 2024, the first TM44 is due by March 2029.

If your system was installed before 2008, you should already be deep into your inspection cycle. If you have never had one, you are non-compliant and you need an assessor on site this quarter.

You also need a fresh inspection if the system is significantly modified. Adding a new outdoor unit, replacing more than 30% of the indoor units, or extending the system to new floors all reset the obligation.

What an inspector actually checks (CIBSE TM44 methodology)

The methodology splits into a simple procedure for packaged and split systems, and a full procedure for centralised plant like chillers and AHUs. Most London commercial buildings get the simple procedure unless they have a chiller serving FCUs.

On the day, an accredited assessor will go through the following:

1. Documentation review. Service records, design drawings, control schedules, previous reports, and equipment schedules.
2. Equipment condition. Refrigerant pipework insulation, condenser coil cleanliness, indoor unit filters, fan condition, and any signs of refrigerant leaks.
3. System sizing. Whether the installed cooling capacity is reasonable for the heat gains in each space. Oversized kit short-cycles and wastes energy.
4. Control strategy. Setpoints, time schedules, deadbands between heating and cooling, BMS integration, and whether occupants have been left with a remote that overrides everything.
5. Simultaneous heating and cooling. One of the most common faults we find in mixed-tenancy offices.
6. Free cooling and ventilation interaction. Whether the system fights with operable windows or fresh air supply.
7. Maintenance regime. Frequency, scope, and whether records actually exist.

The full procedure adds airflow measurements, log analysis from the BMS, and a more detailed look at chiller efficiency. CIBSE's overview of the TM44 inspection methodology sets out both procedures in detail.

A solid grasp of seasonal energy efficiency ratio (SEER) helps here, because the assessor's recommendations often hinge on whether the existing equipment is meeting modern efficiency benchmarks.

Cost ranges in 2026 by system size

Pricing varies a lot by location, system complexity, and how much paperwork the assessor has to chase down. London tends to sit at the higher end because of access, parking, and the prevalence of multi-tenancy buildings.

Here is what we typically quote and what we see in the market in 2026:

System size (effective cooling output)	Typical 2026 cost (ex VAT)	What is usually involved
12kW to 30kW (small office, shop, clinic)	£300 to £550	Simple procedure, 2 to 6 indoor units, single visit
30kW to 100kW (medium office, restaurant, retail flagship)	£500 to £950	Simple procedure, multi-floor, often VRF
100kW to 250kW (large office floor plate, mixed-use)	£900 to £1,800	Mix of simple and full procedure, possible chiller
250kW+ (HQ buildings, hotels, data halls)	£1,500 to £4,000+	Full procedure, BMS log analysis, multi-day on site

If you are pricing inspection alongside repair work, our breakdown of AC replacement costs and the wider running costs of air conditioning in the UK gives a sense of how the inspection sits inside total cost of ownership.

Fines for non-compliance

The penalty regime is set out in the 2012 regulations and confirmed by the gov.uk guidance. The headline number people quote is £300, but it is not the only fine you can receive.

Breach	Penalty	Issued by
Failing to have a valid inspection report when required	£300 fixed penalty per system	Local Trading Standards
Failing to provide a report within 7 days of a request	£200 fixed penalty	Local Trading Standards
Energy assessor offences (false certificates, etc.)	Up to £5,000	Local authority

Enforcement is by Local Weights and Measures Authorities, usually the Trading Standards team at your local council. They tend to act when triggered by something else: a complaint, an EPC commissioning, a MEES review, a sale, or a refinancing due diligence pack.

The bigger commercial risk is not the fine. It is what happens when a buyer's solicitor or a tenant's lawyer asks for the report and you cannot produce it. Deals get held up. Rent reviews get loaded against the landlord. Insurance premiums tick up.

Government MEES reforms tightening EPC standards for commercial property are pushing TM44 closer to the spotlight. The current non-domestic MEES guidance on gov.uk sets the minimum EPC at band E, with proposals to raise it further before 2030. A poor TM44 report can drag your EPC down and put a building in scope of MEES enforcement.

What the report includes and what to do with it

The TM44 report is more than a tick-box certificate. Done properly, it is a useful piece of asset management documentation. It must include:

• Building address and a description of the cooling system
• Total effective rated cooling output
• Assessor name, accreditation scheme, and unique reference number on the national register
• Inspection date
• An assessment of system efficiency and sizing
• Identified faults and a clear list of recommended actions
• An evaluation of the maintenance regime
• Comments on controls and recommendations to improve them
• Key findings summary at the front

You are not legally required to act on the recommendations, but ignoring them is a missed opportunity. Most reports identify quick wins worth thousands per year. Common ones we add to reports:

• Adjusting setpoints and deadbands to stop simultaneous heating and cooling
• Tightening time schedules around occupancy
• Replacing failed filters and cleaning condenser coils
• Recommissioning BMS strategies that have drifted
• Sub-metering tenant cooling loads

Keep the report on file for at least the next inspection cycle. You also need to be able to produce it within seven days of a Trading Standards request, so do not bury it in a contractor's portal you no longer use.

How to make your AC actually pass cleanly

An assessor cannot fail your building outright, but they can write a report that flags every weakness and lands in front of a buyer or a regulator. The aim is a clean report with minimal critical recommendations.

From the inspections I run, the buildings that score well share a few habits:

1. Planned preventative maintenance is in place. Quarterly minimum on critical systems, six-monthly is the floor for everything else. If your last service is more than a year old, expect criticism.
2. Filters and coils are clean. A blocked condenser coil can cut efficiency by 20% or more. We see this constantly on rooftop kit in central London where extract grease and dust build up fast.
3. Controls are documented and behaving. If your BMS shows heating and cooling running together at 11am, the report will say so.
4. The system is right-sized. Oversizing is the silent killer. Worth modelling before any retrofit. See our guide to the best commercial HVAC systems for what current best-in-class looks like.
5. Smart controls are properly configured. Modern smart and energy efficient AC options can knock 10 to 25% off bills if commissioned correctly.
6. You prep for summer. A pre-season check covers most of what an assessor wants to see. Our summer AC preparation checklist is a good starting point.
7. Documentation is one folder, not seven. Service sheets, F-Gas logs, drawings, schedules. Hand it to the assessor on a USB stick or a Dropbox link. They will love you.

If your kit is genuinely past it and the report is going to be brutal no matter what, sometimes the better commercial decision is to plan a replacement. New equipment with a fresh TM44 against it tends to add value at sale and gets you ahead of incoming MEES tightening. Just remember that some replacements need planning permission for new air conditioning units, particularly external condensers in conservation areas.

For commercial buildings inside the M25, we handle TM44 inspections, planned maintenance, and full air conditioning installation in London end to end, so the report writer and the engineer fixing the recommendations are in the same team. That tends to be the cleanest way to keep on the right side of the regulations without three contractors arguing over scope.

If you are unsure whether your system crosses the 12kW threshold, add up the nominal cooling outputs on the data plates of every indoor unit you control. If the total is over 12, you need a certificate. If you are not sure where to find the data plate, that is a separate conversation, and one we can have on a 10-minute site visit.