TM44 Inspection Intervals and F-Gas Checks: Legal Minimums vs Recommended Servicing

How often is a TM44 inspection required, and how often should commercial air conditioning be serviced on top of it? There is no single number, and that is why this question is so frustrating to search. Commercial air conditioning service frequency is really three separate obligations stacked on top of each other. A statutory TM44 inspection is required at intervals not exceeding five years for systems with an effective rated output above 12 kW [1]. F-gas leak checks fall due every 3, 6 or 12 months depending on the refrigerant charge measured in tonnes of CO2 equivalent [3]. Routine servicing, commonly twice a year for offices and shops, is industry practice rather than law — a convention, not a duty, and one we state here on our own account rather than borrowing it from a maintenance company's marketing.

Only the first two are legal minimums. The third is what actually keeps the system running well, and here is the part most guides miss: neglecting it can shorten your statutory inspection interval. In Scotland, accredited experts can set inspection intervals between three years for poorly maintained, inefficient systems and up to five years for well-maintained, efficient ones [2]. Under-servicing does not save you compliance work. It buys you more of it.

What counts as commercial air conditioning under UK rules

The word "commercial" does less work here than the thresholds do. Two numbers decide which duties apply to your system, and neither of them cares whether the building is an office, a shop or a house.

12 kW effective rated output. Above this, the system falls within the statutory air conditioning inspection regime and must be inspected by an accredited energy assessor at intervals not exceeding five years [1]. Crucially, this is the combined effective rated output of all the units serving a building under one person's control, not the rating of a single indoor head. Four 4 kW cassettes in a retail unit clear the threshold together even though each one individually does not.

5 tCO2e refrigerant charge. Above this, F-gas leak-check duties bite. Systems between 5 and 49.9 tCO2e, a band that includes most small commercial and many residential installations, require annual leak checks, or every 24 months where a certified automatic leak detection system is fitted [4].

That second threshold catches people out. A multi-split serving a large house, a converted loft or a garden office can sit comfortably below 12 kW, escaping TM44 entirely, and still carry enough refrigerant to trigger annual leak checks. Assuming domestic scale means exempt is one of the more common mistakes we see. If you are weighing up options at the smaller end, our guide to how often air conditioning should be serviced in UK homes covers the residential side in more detail.

Legal minimums explained: TM44 inspections and F-gas leak checks

These two regimes are often lumped together as "compliance", but they exist for different reasons and are carried out by different people.

TM44 inspections

TM44 is the CIBSE methodology behind the statutory air conditioning inspection introduced under the Energy Performance of Buildings framework. The inspection looks at efficiency and sizing rather than mechanical condition [6]: is the plant oversized for the space, are controls set sensibly, are there straightforward opportunities to cut energy use and emissions? The output is a report with recommendations, lodged on the register, plus a certificate.

An accredited energy assessor must carry it out, and the five-year figure is a maximum interval rather than a target [1]. Requirements and their administration vary across the devolved administrations, so a Scottish portfolio and an English one may not be handled identically [2]. If you hold property in more than one nation, check the position for each rather than assuming the English rules travel.

F-gas leak checks

F-gas duties come from environmental law, are performed by engineers holding F-gas certification [5], and scale with how much refrigerant the system holds:

Intervals are doubled where automatic leak detection is installed [3]. Above 500 tCO2e, leak detection is not merely permitted but required at that charge level [4].

Neither regime is a maintenance schedule. A TM44 assessor will not clean your filters, and a leak check confirms refrigerant is not escaping rather than that the system is running efficiently. Both are snapshots. Meeting them to the letter, and doing nothing else, leaves a system that will quietly degrade between visits.

How often should commercial air conditioning be serviced in practice?

Bi-annual servicing is the accepted baseline for standard office and retail environments, and it comfortably exceeds the legal minimum inspection and leak-check frequencies for most systems in that class. The logic is seasonal: one visit before the cooling season, one before the heating season if the units run as heat pumps, so filters, coils, drainage, electrical connections and control settings are checked ahead of peak load rather than after a failure.

Scale upward from there according to load, not floor area:

• Standard offices and shops — twice yearly is the sensible default.
• Server rooms and comms cabinets — quarterly at minimum. These systems run continuously, and the cost of a failure is measured in downtime rather than discomfort.
• Healthcare and care settings — more frequent attention, driven by indoor air quality expectations, hygiene protocols and vulnerable occupants.
• Gyms, hospitality kitchens, commercial laundries — high heat load, high humidity, airborne grease and dust. Filters and coils foul far faster than in an office, so quarterly servicing is often the honest answer.
• Seasonal or lightly used spaces — an annual service may be defensible, but the F-gas leak-check clock keeps running regardless of how little the system is used.

The variable that matters is running hours combined with air contamination. A 5 kW unit in a dusty workshop running twelve hours a day needs more attention than a 20 kW system in a quiet meeting room suite.

Can poor maintenance shorten your TM44 inspection interval?

Yes, and this is the detail that reframes the whole cost calculation. In Scotland, accredited experts can set statutory air conditioning inspection intervals at three years for poorly maintained and inefficient systems, extending to five years for systems that are well maintained and running efficiently [2].

Read that as a feedback loop. Skip servicing, and the plant drifts: fouled coils, drifting charge, controls left in whatever state the last occupant chose. An assessor arriving to find that picture has grounds to require the next inspection sooner. You then pay for more assessments, on top of higher energy bills, on top of the repairs that deferred maintenance eventually forces. The five-year interval is something a well-run system earns, not a default entitlement.

There is a second, less visible cost. TM44 reports are lodged and their recommendations are on record. A sequence of reports repeating the same unaddressed efficiency findings is not a comfortable document to hand to an incoming tenant, a lender or an insurer. It reads as a building that has been managed reactively.

Regular servicing pulls in the opposite direction. Clean heat exchangers, correct refrigerant charge and properly configured controls all reduce electrical input for the same cooling output, which is exactly what the statutory inspection is designed to probe [1]. The maintenance regime and the compliance regime are not separate concerns; the first largely determines how the second goes.

Who is legally responsible for air conditioning compliance, landlord or tenant?

Responsibility follows control of the system, not the title deeds. The duty to arrange inspections and leak checks sits with the person or organisation that controls the operation of the equipment [1]. In practice that means:

• Owner-occupied premises — the business occupying the building.
• Single-let commercial property — usually the tenant, where the lease hands over the plant and its operation. Read the lease; do not assume.
• Multi-let buildings with landlord-operated plant — the landlord or their managing agent for shared systems, the tenant for any equipment they control within their demise.
• Managed portfolios — a facilities manager may deliver the compliance work, but the underlying duty stays with whoever controls operation.

Control can move mid-tenancy, at lease assignment, or when a managing agent changes. When it does, TM44 inspection reports must be passed on, and F-gas records for the equipment should travel with it [1][3]. A new occupier who cannot produce the last inspection report has no way to prove the interval has been met, and no baseline for the recommendations already made.

Landlords in particular should be explicit about this in heads of terms rather than discovering the gap at renewal. Our page on air conditioning obligations for commercial landlords goes further into how these duties are usually allocated.

TM44 inspections and F-gas checks in practice: four examples

Four scenarios, showing how differently the three obligations combine.

A 15 kW VRF system in a high street retail unit, 12 tCO2e charge. Above the 12 kW threshold, so a TM44 inspection by an accredited assessor at intervals of no more than five years [1]. In the 5–50 tCO2e band, so annual F-gas leak checks [4]. Recommended servicing: twice a year. Three separate visits in a typical year, only two of them legally mandated.

A 40 tCO2e office system across three floors. Same TM44 duty. Still annual leak checks, because 40 tCO2e sits inside the 5–50 band [3]. Bi-annual servicing, and worth reviewing after any partitioning changes, since a TM44 assessor will comment on sizing against the space actually served [6].

A healthcare facility with 600 tCO2e of plant. Leak checks at least every 3 months, and automatic leak detection is required at this charge level, which permits 6-monthly checks instead [4]. TM44 applies. Servicing frequency is set by clinical air quality requirements rather than by regulation, and quarterly or better is the norm.

A 9 kW split system serving a server room, 6 tCO2e. Below 12 kW, so no TM44 inspection. Above 5 tCO2e, so annual leak checks still apply [4]. Continuous operation means quarterly servicing regardless. The system with the fewest statutory duties here needs the most frequent attention.

TM44 inspection FAQs

How often should commercial air conditioning be serviced by law in the UK? Servicing itself is not directly mandated by frequency. What the law requires is TM44 inspection at intervals not exceeding five years above 12 kW [1] and F-gas leak checks every 3 to 12 months by refrigerant charge [3]. Bi-annual servicing is industry practice layered on top.

Is bi-annual servicing a legal requirement? No. It is a widely recommended baseline for offices and retail, not a statutory duty. It does, however, help you keep the longer TM44 interval [2].

Do small commercial split systems need F-gas leak checks? If the charge is 5 tCO2e or more, yes: annual checks, or every 24 months with certified automatic leak detection [4]. Falling below 12 kW exempts a system from TM44, not from F-gas.

What records do I need to keep? Leak-check and refrigerant-handling records under F-gas [3][4], and TM44 inspection reports, which must be retained and handed on when control of the system changes [1]. Ask your maintenance provider for documentation as a matter of course, not on request.

Can a TM44 interval really be cut to three years? In Scotland, accredited experts set intervals from three years for poorly maintained and inefficient systems up to five for well-maintained ones [2]. Requirements vary by administration, so check the guidance for the nation your building sits in.

Building a compliant air conditioning maintenance schedule

Start with two figures, because everything else follows from them: the combined effective rated output in kW of the systems under your control, and the refrigerant charge in tCO2e. Your installer's commissioning paperwork or the unit nameplates will give you both. From there, log the date of the last TM44 inspection and the date of the last leak check, and diarise the next ones against the correct interval rather than against memory.

Then set the servicing rhythm by how hard the plant works, not by what the regulations require. Twice a year for a standard office; quarterly where the system runs continuously or the air is dirty.

Keep the paperwork somewhere a successor can find it. The awkward conversations happen not when a system fails, but when someone asks for a five-year-old inspection report and nobody knows who held it. If you would rather not reverse-engineer your obligations from nameplates, ask for a written schedule against your actual kW and tCO2e figures, and check the planning and compliance requirements that apply before any new installation is specified.