Warehouses rarely look like the textbook examples often used to explain air conditioning assessments. They are vast, draughty, and full of microclimates that shift with loading schedules and seasons. Forklifts open doors for minutes at a time, mezzanines trap heat, and small server corners hum along in a sea of ambient air. That is why TM44 inspections in warehousing call for a different approach from what suits an office block. Do the fundamentals apply? Yes. But the way you test, question, and recommend must respect the peculiarities of logistics operations, racking layouts, and mixed-use spaces.
This playbook sets out how to approach TM44 compliance in warehouses pragmatically. It blends formal requirements with methods learned on genuine inspections, including when to be flexible, when to push for change, and where to focus if you want energy savings that matter.
What TM44 actually requires, without the fluff
TM44 is the guidance document for air conditioning inspections required across the UK. If your site has one or more air conditioning systems with a combined rated cooling capacity over 12 kW, you need a periodic inspection by an accredited assessor. The interval is typically every five years, though some organisations voluntarily tighten the cadence to keep a closer grip on energy use and equipment condition.
The inspection must produce a report with three core outputs: an assessment of the system’s efficiency and sizing, a review of maintenance and controls, and recommendations that are technically and economically viable. TM44 does not mandate specific upgrades, it mandates competent advice with a focus on realistic savings and risk reduction. For warehouses, that means fewer generic “install variable speed drives” lines and more pointing out where a dock door, left cracked open all day, is undoing every good intention.
TM44 does not replace F-Gas obligations, health and safety requirements, or landlord-tenant maintenance duties. It sits alongside them. If you see a refrigerant label and think the job is done, you are missing the point.
TM44Warehouse realities that affect the inspection
On paper, a warehouse is a simple envelope. In practice, it is a set of zones with very different loads and occupancy patterns. I look for five recurring conditions:
- Patchy cooling coverage. The offices over the reception are overcooled because someone hates heat, while the packing area’s split units fight solar gain all afternoon. Dock door losses. Each door acts like a 50 square metre hole, sending cooled air straight into the yard. Even a slight warp or worn bottom seal can drop effective cooling by a double-digit percentage. Internal heat islands. Conveyor motors, shrink wrappers, UPS cabinets, and server racks can turn a corner of the building into a micro data hall that never quite reaches setpoint. Controls drift. BMS schedules are copied from winter to summer without adjustment. Manual overrides on splits become permanent. Night-setback modes are left off because “someone once had condensation.” Hidden maintenance gaps. Filters are changed, coils not so much. Condensate drains sludge up silently. Access hatches are blocked by pallets.
None of these are unusual. They are part of warehousing. A credible TM44 inspection acknowledges them and still proposes actions that fit the way the building runs.
Scoping the inspection with a warehouse lens
Before walking the floor, I want three things: an up-to-date plant list with model numbers and nameplate ratings, floor plans with HVAC marked, and a frank conversation with the operations lead. Warehouse managers often know exactly where staff complain about heat or where product quality risks spike.
Map the system boundaries early. Many warehouses mix packaged rooftop units, ducted splits for offices, and wall-mounted splits for zones like rework rooms. Cold rooms and process chillers often sit outside TM44 scope unless they provide comfort cooling, but they still matter. If a chilled space leaks cold into a packing area that relies on split systems, those splits are carrying extra load that changes your recommendation.
I also check operational windows by zone. Despatch might run 24 hours Monday to Friday in a regional hub, but only two shifts in a local facility. Offices may close at 6 pm, yet the units hum through the night because the BMS schedule was cloned years ago. Data like this shapes the energy angle and shows where to tighten schedules without hurting operations.
Document review that actually informs the site walk
TM44 asks for maintenance records, energy data if available, and control strategies. Many warehouses show a folder with annual service sign-offs and little else. You can still extract value. I look for:
- Frequency and depth of filter and coil cleaning compared to dust levels on site. Fault codes recorded on visits and whether they recur, often hinting at refrigerant charge issues or board faults. Any commissioning sheets for newer splits or packaged units, especially fan speeds and refrigerant weights.
If there is metered sub-circuit data for HVAC, even better. You can spot baseline cooling consumption versus seasonal variation. If not, use half-hourly main electricity data and cross-check against weather and shift patterns. A flat overnight profile in the office block is usually a schedule problem, not an exception.
The site walk, step by step, tuned for warehouses
The physical inspection is where TM44 earns its keep. You cannot do this credibly from a desk.
Start with the envelope. Stand at the loading bays and watch a complete docking cycle. You will learn more in ten minutes than in a stack of manuals. Note how long the doors stay open, whether shelters seal properly, and if dock leveler pits are airleaky. Ask how often doors are kept on latch in hot weather. If fabric losses are huge, your recommendations for AC are going to be band-aids unless you address air paths.
Move to each air conditioned zone and test the basics. Measure supply air temperature at the diffuser or unit grille, return air temperature, and ambient nearby. If the difference fails to hit an expected delta (commonly 8 to 12 K for direct expansion equipment under steady load), suspect coil fouling, low refrigerant charge, or poor airflow. In warehouses with high dust, even two months can load a filter heavily.
Check sensor placement. I have seen wall controllers directly under a de-strat fan. The system short cycles and never holds a sensible setpoint. In mezzanine offices, sensors near the stair opening see heat plumes from below and drive unnecessary cooling. Relocating a £50 sensor can save hundreds a year.
If there is a BMS, sit with it. Verify that time schedules reflect reality, not old patterns. Confirm deadbands and interlocks between heating and cooling. In mixed-mode spaces, install a deadband of at least 2 K, ideally more, so the two systems do not overlap. It is remarkable how often both sit active between 19 and 21 Celsius because someone wanted “tight control.”
Walk the roof. Packaged units tell the truth up there. Check coil fin condition, corrosion on frames, degraded insulation, perished flexible connections, and clearances around outdoor units. Warehouse roofs collect debris and wind-blown dust, which stick to coils and cut heat rejection. I carry a simple manometer probe for filters and a thermal camera. A hot discharge line with a warm condenser coil can point to fan faults or blocked fins.
Look at condensate routes. In dusty environments, drains silt up. You may see overflow staining on walls that never made it into the logbook. That is a mould and hygiene risk as well as an efficiency issue.
Server corners deserve attention. Many warehouses have a small comms room fed by a wall split. If the room is not sealed, hot air spills into a corridor and the unit runs flat out forever. Even simple containment with door seals and a dedicated return path can decrease runtime. If redundancy is required but not present, flag it. TM44 expects you to identify risks to reliable operation, not just energy concerns.
Sizing and diversity in large, open volumes
TM44 requires an opinion on system sizing. In warehouses, this is delicate. The building volume is enormous, but you rarely need to condition all of it. The trick is to consider the active zones and diversity, not the envelope cubic metres.
I build a quick view of sensible heat loads for each zone that genuinely needs comfort conditions. For packing areas with 15 people and equipment running, add internal gains from bodies, motors, and lighting. For offices, use standard office loads adjusted for occupancy. Dock areas might only need spot cooling for a supervisor desk. If the installed capacity in a zone exceeds the calculated load by more than, say, 30 to 40 percent without a clear reason, it is worth highlighting. Oversized splits tend to short cycle, never dehumidify properly, and cause comfort complaints despite being “big enough.”
On the flip side, many warehouses under-specify cooling for “temporary” areas that become permanent. A rework bay will start with one unit, then racks block airflow, staff multiply, and the unit limps along at 100 percent duty. Call it out. Overstressed kit fails at the hottest time of year, exactly when availability matters most for throughput.
Controls that match the choreography of a warehouse
If I had to pick one lever for TM44 recommendations in warehouses, it would be controls. Proper setpoints and schedules beat expensive hardware swaps for pure payback.
Treat setpoints as policy, not preference. Offices should sit at a realistic band, for example 23 to 25 Celsius in summer, if staff attire and duties allow. Warehouse floors with active work have a wider comfort tolerance. The energy penalty per degree of cooling is significant. If the manager sets 20 because “it feels fresher,” expect the plant to fight a losing battle whenever the doors open.
Night and weekend control separates mature sites from ones on autopilot. A 3 to 5 K setback out of hours is a safe default in most office zones, with exceptions for IT rooms. Do not shy away from recommending lockouts or access control on wall controllers to prevent drift. Cases of tampering are common in mixed-use buildings, especially if staff assume turning it colder makes it cool faster.
Interlocks between heating and cooling matter in spring and autumn. Warehouse offices often have electric panel heaters or LTHW radiators on separate thermostats. Without a proper deadband and lockout, one fights the other. TM44 is explicit about avoiding simultaneous heating and cooling. Spell out the control change needed in plain language, with point names if a BMS is present.
Maintenance that accounts for dust, doors, and downtime
The standard service contract often reads tidy on paper but fails on frequency. Dustier warehouses need more frequent filter changes and coil cleaning. That is not a sales pitch, it is physics. If prefilters do not exist upstream of coils in high-dust zones, recommend them. Disposable panel prefilters cost little and extend coil life.
Outdoor units on roofs need protection from bird nesting and debris drift. Guards are fine, but guards reduce accessible coil area if installed too close. Specify clearances and confirm that airflow is not choked by the protection.
Consider the reality of access. If a unit is wedged above a mezzanine corridor with no safe way to reach it, it will not be maintained properly. You can recommend moving it, adding a platform, or reconfiguring ductwork. TM44 allows you to comment on maintenance feasibility. Use that permission wherever the current setup guarantees shortcuts.
Spare parts and lead times are worth a note. For legacy R22 replacements long completed, some warehouses still run older R410A splits with boards and sensors that have multi-week lead times. If the site is mission-critical during summer peaks, suggest keeping a small stock of common spares or pre-agreed supplier SLAs.
Energy opportunities that are not just boilerplate
It is easy to type “install EC fans, add variable speed drives” and call it a day. In warehouses, more grounded opportunities tend to pay back faster.
Dock door discipline is number one. If doors are open unnecessarily for 20 minutes per hour, you are air conditioning the yard. Fit door interlocks to prevent prolonged open states, add simple visual timers at operator stations, and repair seals. I have seen 10 to 20 percent HVAC savings in packing zones from door management alone.
Destratification fans help in winter for heating, but in summer they can spread heat from high-level lighting or a hot roof skin. Use them judiciously. If AC is serving a ground-level area, consider switching de-strat fans off in that zone during the hottest hours to prevent the system constantly mixing in hotter air.
Sun control often beats tonnage. If a packing area has south-facing glazing, internal film or external shading can drop peak loads materially. Splits that were under strain suddenly have capacity in reserve.
Zoning is a quiet hero. Many warehouses cool an entire office wing evenly despite occupancy varying by the hour. If ductwork allows, zone dampers tied to occupancy schedules reduce runtime. In small systems, installing smart thermostats with occupancy detection recoups cost within a season.
For packaged rooftop units with older controls, a retrofit economiser cycle can deliver cheap cooling when outdoor conditions permit it. UK climates offer shoulder-season hours where free cooling is viable in non-dusty zones. Be cautious with air quality near loading bays, and include filtration upgrades if you pursue this.
Making the recommendations land with operations
Good TM44 advice fails if it reads like theory. You need to present each recommendation with a brief “how it fits this site” note, a likely cost tier, and an operational caveat where relevant. For example, do not just say “tighten schedules.” Say “reduce office block AC runtime from 24/7 to 0600 to 1900 weekdays, with a 3 K night setback and weekend off except for comms room. Confirm with HR that cleaning shifts are complete by 1900.”
Be open about trade-offs. Interlocking dock doors may slightly slow turnaround on low-volume night shifts. If the site values speed above all else, consider a seasonal approach, tightening controls only in the hottest months. This is not a cop-out; it is a way to gain acceptance.
Where capital is needed, steer toward measures that do not demand structural change. Retrofitting demand-controlled ventilation in office areas with CO2 sensing is one. Replacing individual noisy splits with a small VRF in a reconfigured office cluster is another, as long as the pipe runs are feasible.
A lean data set to track after the inspection
TM44 does not require ongoing monitoring, but a simple post-inspection dataset helps validate changes. If the site has no sub-metering, pick two or three indicators:
- Weekly kWh from the main meter during comparable weather periods, annotated with shift patterns. Average indoor temperatures at two representative zones using cheap data loggers, especially the chronic hotspots. Number of door-open minutes per hour at the busiest dock, using the dock controller’s logs if available.
These are not perfect, but they give enough feedback to sustain improvements and justify further tweaks.
Edge cases and tricky calls
You will run into situations where the right answer is not obvious.
Mixed heating and cooling zones in one large space can create control conflicts. If heating is via gas-fired unit heaters on a separate control scheme, and cooling is via splits around supervisor desks, you need to set wider deadbands and perhaps limit heating operation after temperature reaches a safe minimum. Comfort will fluctuate more, but energy waste drops. The right balance depends on product requirements and HR policies.
High-bay LED retrofits change the thermal picture. Older metal halide or fluorescent fittings threw off heat that AC had to reject. New LEDs cut internal gains, which could justify turning down fan speeds or rebalancing air distribution. If your inspection follows a lighting upgrade, account for it in load discussions.
Enclosed pick towers behave like buildings within buildings. They hold heat on upper levels even with modest occupancy. If the tower has local splits, put sensors on the second level, not the ground, and accept that airflow at floor level may not reflect actual operative temperature.
Verifying compliance and avoiding paperwork traps
TM44 compliance is not hard to demonstrate. Keep a tidy pack: the assessor accreditation details, a report with identified systems, findings, and recommendations, and the site’s obligation date for the next inspection. Landlords and tenants should both retain copies, because disputes about responsibility for controls and maintenance surface when costs spike.
The common traps are simple. Do not forget small systems that add up to more than 12 kW combined. A row of 3.5 kW wall splits across a mezzanine counts. Do not assume process cooling is out of scope if it conditions people too. If staff work in a process-cooled space for long stretches, that system deserves review for comfort controls even if the primary purpose is product.
Finally, make sure advisory notices are intelligible. A manager should understand what to do without reading a controls manual. Avoid boilerplate text, explain the site-specific fix, and provide a point of contact for clarification.
A realistic timeline for a typical warehouse assessment
For a single-building warehouse of roughly 8,000 to 15,000 square metres with a mix of offices and three to six AC systems, allow a day to a day and a half on site and two to three days to compile a high-quality report. Larger sites with distributed blocks or multiple rooftop units require more time, especially if access is complex. Plan roof access in advance, including permits and safe routes. Do not underestimate the time to trace pipework runs on older installations where drawings are missing.
I like to schedule at least one walkthrough during peak activity and one during a quieter window. You learn different things each time, and operations appreciate that you did not block workflow.
What a good TM44 report for a warehouse sounds like
It reads specific, not generic. It names units, cites observed temperatures, and describes control changes in practical terms. It quantifies, even with ranges. “Changing office AC schedules is likely to save 8 to 12 percent of annual cooling energy in that zone” is more persuasive than “significant savings possible.” It flags health and safety concerns such as blocked access or suspect electrical isolation on packaged units. And it respects the warehouse’s mission: moving goods safely and on time.
The best reports also seed future conversation. Perhaps the AC plant is fine, but the data suggests a HVAC zoning project tied to a planned office refurbishment could consolidate two systems into one efficient VRF solution. You do not need to design it in the report, only show the path.
A short, pragmatic checklist for the final pass
- Confirm combined cooling capacity over 12 kW, list all qualifying systems, and capture serial plates. Verify time schedules, setpoints, and heating-cooling deadbands in every conditioned zone. Measure quick temperature deltas at representative units, note any outliers, and inspect coils and filters. Observe dock operations for leakage and dwell time, and note fabric or seal issues that affect cooling. Produce recommendations with site-specific actions, rough cost tiers, and operational notes.
The payoff
Warehouses do not need perfect climate control everywhere, they need targeted comfort where people work and protection where products demand it. TM44, used thoughtfully, nudges sites toward that balance. It spots wasted runtime, finds the overlooked filters and blocked coils, and nudges controls into alignment with actual shifts. The savings are not abstract. They show up as fewer nuisance calls during heatwaves, fewer staff complaints in offices, and monthly energy totals that stop creeping up year after year.
Most of all, a solid TM44 inspection respects how a warehouse breathes. It treats doors, mezzanines, heat islands, and schedules as part of the cooling system, because they are. When you approach it that way, compliance turns into practical stewardship rather than a tick-box exercise, and the building starts working with the plant instead of against it.