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Ventilation duct cleaning: what TR19 Air expects

Updated 23 October 2026 · SEO Dons Editorial

What is TR19 Air, and is it a legal requirement?

TR19 Air is BESA's specification for the internal cleanliness and hygiene management of ventilation systems. BESA describes it as best-practice standards for keeping ventilation systems in commercial and public buildings clean. BESA's publication page lists the March 2026 edition, with post-clean reporting added as a new section 9, a reference to the Ventilation Hygiene Register and added detail on ductwork sensors. BESA traces the line back to a specification first developed in 1991, and says grease fire risk in kitchen extract now sits in a separate document, TR19 Grease.

It is a specification, not a statute. The legal duty sits in regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992, which requires effective and suitable provision so that every enclosed workplace gets enough fresh or purified air. HSE adds that mechanical ventilation needs to be properly maintained. BESA's position is that TR19 Air helps building owners, operators, contractors and consultants meet their legal obligations under those regulations, as well as BS EN 15780 and other standards. For new work in England, Approved Document F Volume 2 also asks for access points for cleaning ductwork and for operating information that says how often cleaning should be done.

How is duct cleanliness measured?

BESA says the first step is a visual inspection to assess condition and decide whether cleaning is needed. Measurement follows. BESA says TR19 Air sets measurable cleanliness levels for both new and existing ductwork and applies to new construction, refurbishment and routine maintenance, so a new system can be checked at handover as well as an old one.

MethodWhat it measuresBESA's note
Visual inspectionCondition of the internal surfacesThe first step, and the way to decide whether cleaning is required
Deposit thickness testMean surface deposit thickness, in micronsUsed before and after cleaning
Preferred vacuum testDust deposited, by weight in grams per square metrePart of BS EN 15780; particularly useful for newly installed systems

BESA also describes three BS EN 15780 cleanliness classes. Low risk covers rooms with only intermittent occupancy, such as storage and technical rooms. Medium risk covers offices, hotels, restaurants, schools and similar spaces. High risk covers laboratories, hospital treatment areas and other specialist settings. For medium risk buildings BESA quotes a dust level of less than 3.0 grams per square metre. Read the current specification for the exact limits, because only it is authoritative.

How often should ductwork be inspected, and what brings a clean forward?

BESA describes a risk-based approach for general supply and extract systems. Occupancy levels, system age, location and the activities in the space should inform the schedule, and TR19 does not impose rigid intervals for every system but promotes regular assessment supported by measurable standards.

SettingInterval BESA's guidance describes
Offices, schools and other occupied commercial spacesA baseline inspection typically every 12 months, with cleaning when deposit levels or the system's condition call for it
Any system, under TR19BESA's FAQ says TR19 recommends inspections should not exceed 12-month intervals
Most facilities, under BS EN 15780Inspections every two years as a minimum
Healthcare, laboratories, cleanrooms, under BS EN 15780Annual inspections
Kitchen grease extractSeparate specification: see the TR19 Grease guide

The 12-month TR19 figure is tighter than the two-year BS EN 15780 minimum, so a planner has to choose which governs. Treating the shorter interval as the working assumption is the cautious route, and BESA says the schedule should be documented within the building's planned preventative maintenance programme.

Cleaning can come sooner. BESA says damp, neglected ducts favour fungal spores and bacteria, and that in commercial settings such ducts can become reservoirs whose contents recirculate through the air system. BESA's technical director also said accumulated debris can obstruct airflow, forcing fans to work harder. Leakage wastes fan energy too, and the DW/144 leakage guide explains how that is tested.

What does a TR19 Air clean and report include?

BESA says the method must be chosen on system type, contamination level and accessibility. For general air systems it lists vacuum cleaning with HEPA-filtered units for dry dust, compressed air agitation with brushing or vacuuming, and rotary brushing for inaccessible runs. Chemical applications target grease or biological contaminants and must be followed by thorough rinsing.

After the clean, BESA says the verification report should include:

  • photographs of the same positions before and after the clean;
  • deposit thickness readings from before and after;
  • a plan showing which areas were cleaned;
  • a record of the access points that were, and were not, available;
  • a hygiene certificate giving the date, system type, location and contractor.

Keep these with the maintenance log, because they are the evidence that the work was done to a recognised standard. A cleaning scope should also name the systems, the access limits, the test method, the pass level and the report format before work starts, so quotes can be compared like for like.

What about access panels, fire dampers and indoor air quality?

BESA says ductwork cannot be properly inspected or cleaned without adequate access, and that TR19 expects designers to provide it, both through the building fabric and into the system. Approved Document F Volume 2 says the same in building-regulation terms for new work.

Fire dampers depend on the same panels. BESA lists dust and debris on damper blades among the frequent obstructions found during damper testing, and says regular cleaning during annual inspections prevents that failure mode. Approved Document B Volume 2 asks for access to a fire damper and its actuator for inspection, testing and maintenance. The HVAC dampers guide covers the testing duty. Clean ducts also matter for indoor air quality, and the commercial ventilation and MVHR page covers the wider system.

Who should carry out the cleaning?

BESA says specialists may be needed where ductwork is high-level or hard to reach, where the insurer requires certified contractors, or where the system serves high-risk settings such as hospitals or food production. In-house work may suit basic inspections of accessible general ventilation in low-risk environments. BESA's Air Hygiene Technician course, for example, is aimed at people who clean and also write risk assessments and method statements, fit access panels, and inspect, test and report on system cleanliness, so ask what training the operatives hold. BESA's publication page says the Vent Hygiene Register would expand from 3 March 2026 to cover TR19 Air as well as TR19 Grease, and BESA warns that some companies show the register's logo without being registered, so check the register itself. Ask each bidder for a method statement, a sample report in the format above and proof of the operatives' training, so the quotes cover the same scope. The guide to choosing an HVAC contractor covers general checks. You can send an enquiry through the form on this site.

Sources

Common questions

TR19 Air is a specification, not a statute. The legal duty is regulation 6 of the Workplace (Health, Safety and Welfare) Regulations 1992, which requires sufficient fresh or purified air in every enclosed workplace, and HSE says mechanical ventilation needs to be properly maintained. BESA's view is that TR19 Air helps duty holders meet those obligations.

Does TR19 Air cover kitchen extract ducts?

No. BESA says grease fire risk in kitchen extract systems is now handled separately, under TR19 Grease. The kitchen guide on this site sets out how that specification works.

What is a deposit thickness test?

BESA describes it as a way of measuring the average thickness of deposits, in microns, on a duct's inner surfaces. It is taken before and after cleaning, so the report shows both readings.

Can duct cleaning be done in-house?

BESA says in-house work may suit basic inspections of accessible general ventilation in low-risk environments. It says specialists may be needed for high-level or difficult-to-access ductwork, where an insurer requires certified contractors, or in high-risk settings such as hospitals.

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