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Commercial air conditioning cleaning: what to clean and how often

Updated 23 October 2026 · SEO Dons Editorial

What needs cleaning on commercial air conditioning?

Five parts collect the dirt that matters: filters, indoor coils, outdoor coils, condensate trays and drains, and fans. Ductwork is a sixth where the system is ducted. The table says what each does when it fouls, using the government's air conditioning inspection guide where it speaks to the point, and who normally cleans it.

PartWhat happens when it foulsWho normally cleans it
Filters, grilles and pre-filtersObscured ones add resistance to airflow, so more energy is needed or the system under-performsSite staff for accessible filters where the unit manual allows; the contractor for ducted and air handling unit filter banks
Indoor coilLess heat moves into the refrigerant circuit, capacity falls, and the unit may cut out on low temperature or pressure without meeting the loadContractor
Outdoor coilBlockage by dirt or debris reduces heat rejection, efficiency and cooling capacityContractor
Condensate tray and drainSlimy debris builds up and stops condensation flushing away; water puddling in a unit can cause electrical damageContractor
Fans and air deliveryFans are likely to use more energy over a year than the refrigeration plant, so any airflow restriction carries a costContractor
DuctworkDust and debris can restrict airflow, reduce energy efficiency and compromise indoor air qualityA ventilation hygiene specialist (see the duct cleaning guide)

Is cleaning a legal requirement?

The law sets a duty to maintain, not a cleaning interval. Regulation 5 of the Workplace (Health, Safety and Welfare) Regulations 1992 says the systems it covers, which include mechanical ventilation systems, must be maintained, including cleaned as appropriate, in an efficient state, in efficient working order and in good repair. HSE's ventilation guidance says to make sure mechanical systems are maintained in line with manufacturers' instructions, and that recirculated air should be adequately filtered. The government's inspection guide adds that inspection, maintenance and cleaning programmes keep the system able to provide healthy and comfortable environments, limit the escape of refrigerant gases and ensure the safety of equipment.

How often should it be cleaned?

No source checked for this page gives one interval for commercial plant, and the figures in circulation vary with the unit. For room units, Daikin recommends cleaning the air filters every 2 weeks, while Hitachi suggests every 3 - 6 months depending on location and frequency of use, with key moments in the weeks before summer and winter. Both are written for room units, so for commercial plant the starting point is the manufacturer's manual. CIBSE says to maintain ventilation systems as advised by the supplier or installer and, without that, points to SFG20.

SFG20 is the usual specification. It was created by BESA, and its schedules define what needs maintaining, how often and by whom. Its task lists are reached through SFG20's own software, so this page does not reproduce them. Two CIBSE points help anyone reading a schedule: filter maintenance can be based on time or on condition, and filter life depends on the concentration and nature of the contaminants and the efficiency of the filter.

Site conditionWhat changesWhat to ask the contractor
Dusty or polluted surroundingsFilters load faster; HSE says air from heavy traffic or smoke should be filteredWhether filters are changed by condition (pressure drop) as well as by calendar
Commercial kitchensBESA says TR19 sets how often to clean kitchen extract ducts, depending on usageThe TR19 report for the extract; see the grease extract cleaning guide
Plant that runs around the clockNo quiet period for cleaningHow cleaning is planned around standby units; see the server room cooling guide
Roadside, car park or leafy sitesDirt or debris can block outdoor coil airflowOutdoor coil condition recorded at each visit

What does dirt do to capacity and running cost?

Official guidance describes the mechanism rather than a percentage. If outdoor heat rejection is blocked, the guide says its effectiveness falls and its temperature rises, which reduces refrigeration efficiency and cooling capacity. A restricted indoor coil has a similar effect and may make the plant cut out on its own temperature or pressure limits, often without satisfying the building's cooling load. No percentage is quoted here because the sources checked give no reliable figure for commercial plant; a figure on a contractor's page is a claim to test.

The energy assessor in a TM44 inspection looks for indicators of damage or lack of maintenance that would significantly reduce efficiency. The guide says cleaning is not part of that inspection, even where it could be done simply and improve efficiency. The TM44 guide covers the duty.

Which coil-cleaning methods and chemicals are appropriate?

The manufacturer's instructions decide. Daikin says not to use a commercial cleaning agent inside a unit, because it may harm the resin parts of the heat exchanger or other internal components. LG says cleaning fins and coils means taking the front section apart, exposing sharp surfaces and electrical components, and recommends a professional service. CIBSE lists vacuum and steam as cleaning methods for ventilation systems and cautions against brushes or compressed air for removing dust from surfaces or from inside machinery. Anything chemical is a COSHH matter, since HSE says the regulations require employers to plan, manage and monitor substances hazardous to health.

Questions to put to a contractor before a coil clean:

  1. Which method will be used on each coil, and does it follow the manufacturer's instructions for that unit?
  2. Which chemical, with its safety data sheet and COSHH assessment?
  3. How will electrics, controls and the ceiling void be protected, and the rinse water captured?
  4. What evidence will be left? BESA says TR19 duct cleaning requires photographs before and after from identical positions, and the same idea suits coils.
  5. Does any of the work touch the refrigerant circuit? If so, certified people are needed.

What is the difference between a clean and a service?

JobWhat it coversWho does it
CleanFilters, coils, trays and drains, fans, ductsStaff or contractor, as the unit manual allows
ServiceRefrigerant-side checks, leak checks and records, electrics, controls, performance readingsA company certified for F gas work on equipment it does not own
InspectionEnergy efficiency assessment of systems above 12 kW, at intervals not exceeding five yearsAn energy assessor; cleaning is not part of it

GOV.UK says a company must be certified by an approved body to service stationary equipment containing F gas that is operated by others. What a servicing price includes, and how to compare quotes, is on the air conditioning servicing cost page. Smells are often the first sign that a clean is overdue, as the guide to why commercial air conditioning smells explains, and the maintenance contract checklist shows where cleaning belongs in a contract. Readers who want quotes can send an enquiry through the site's form.

Sources

Common questions

Can site staff clean the filters themselves?

Only where the unit's manual allows it and the supply is isolated. Hitachi says to turn the power supply off before any cleaning or maintenance, and both Hitachi and Daikin describe filter washing for their room units. Filter banks in ducted systems and air handling units are normally a contractor's job.

How do I know when a filter needs changing without a schedule?

CIBSE says filter maintenance can be based on time intervals or on condition. Condition means watching the rise in pressure loss across the filter, which depends on the contaminants, the filter's efficiency and its dust-holding capacity. Ask the contractor what pressure reading triggers a change.

Does a coil clean count towards the TM44 inspection?

No. The government guide says cleaning operations and control adjustments are not part of the inspection procedure, and the duty itself is for an energy assessor to inspect the system at intervals not exceeding five years. A clean and an inspection are separate jobs.

Is duct cleaning part of an air conditioning clean?

Not unless the contract says so. Ductwork hygiene has its own specification, TR19, which BESA describes as the industry's recognised standard for the internal cleanliness of ventilation systems. Ask whether ducts are inspected, and how often, in the same contract.

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