What TR19 actually is
TR19® is the BESA (Building Engineering Services Association) guide to good practice for internal cleanliness of ventilation systems. It's the recognised UK benchmark for assessing, cleaning and verifying the cleanliness of ductwork and associated plant.
It isn't a single law, but it's the document that everyone — building owners, FM contractors, insurers, fire risk assessors and enforcement officers — treats as the definition of an acceptably clean ventilation system. If your ductwork cleanliness is ever questioned, TR19 is the yardstick it will be measured against.
TR19 Air vs TR19 Grease
Since 2019, BESA has split the guidance into two clearer strands. TR19® Air covers general ventilation hygiene — the supply and extract ductwork serving offices, schools, hospitals and other occupied spaces, where the concern is air quality and system performance.
TR19® Grease covers kitchen extract systems, where deposited grease is a serious fire risk. This is the strand insurers care about most: a grease-laden extract duct is one of the most common causes of catastrophic commercial-kitchen fires.
Knowing which applies to you matters. A restaurant or staff canteen needs TR19 Grease for its kitchen extract and may also need TR19 Air for its general ventilation. An office typically needs only TR19 Air.
Why it matters — fire, hygiene and insurance
Fire safety. Grease accumulation in kitchen extract ductwork is highly combustible. The Regulatory Reform (Fire Safety) Order 2005 places a duty on the 'responsible person' to manage fire risk — and a neglected, grease-laden extract system is a clear, documentable failure of that duty.
Insurance. Most commercial insurance policies for premises with commercial kitchens now require TR19 Grease-compliant cleaning at a stated frequency, with certification. After a fire, insurers routinely ask for cleaning records — and a missing or non-compliant record can invalidate a claim.
Air quality and health. For TR19 Air systems, dirty ductwork degrades indoor air quality, spreads contaminants and reduces system efficiency. In healthcare, this connects to HTM 03-01 and infection-control obligations.
What gets cleaned — and how
A TR19 clean addresses the internal surfaces of the ductwork, not just the visible grilles. That means accessing the duct runs via existing or newly-fitted access panels, mechanically cleaning the internal surfaces, and cleaning associated components — fans, filters, dampers, and in kitchen systems the canopy, plenum and grease filters.
For grease systems, the goal is to reduce grease deposit thickness to the level TR19 Grease specifies. For air systems, cleanliness is assessed against a measured surface-deposit standard. The work should be carried out by trained operatives with the right equipment — high-powered extraction, rotary brushing and, where needed, specialist access.
How often should ductwork be cleaned?
TR19 frequency is risk-based, driven by how heavily the system is used. For kitchen extract under TR19 Grease, the typical guidance is: heavy use (12+ hours/day) every 3 months, moderate use (6–12 hours/day) every 6 months, and light use (2–6 hours/day) every 12 months.
For general ventilation under TR19 Air, frequency depends on the system and occupancy, but an annual assessment is a sensible baseline, with cleaning triggered when measured deposit levels exceed the standard.
The honest position is that frequency should follow a documented assessment of your specific system — not a calendar pulled from thin air. A competent provider measures, then recommends.
Verification and certification
TR19 cleaning isn't finished when the ductwork looks clean — it's finished when cleanliness is measured and certified. Post-clean verification uses standardised tests (deposit-thickness measurement for grease, surface-sampling for air) with before-and-after evidence, typically including photographs and access-point records.
You should receive a certificate and a report that an insurer or fire risk assessor will accept: what was cleaned, the verified result against the TR19 standard, and the recommended next clean date. That certificate is the document that protects you — keep it with your fire safety records.