What do BS EN 15780 and TR19 Air say about duct cleaning frequency?

BS EN 15780 sets three classification levels for ventilation systems (Low, Medium, High) based on building use, which determine how frequently systems should be inspected rather than cleaned. TR19 Air provides recommendations for how often different parts of the ventilation system should be cleaned, with cleaning only required once measured contamination exceeds the defined threshold for that classification.

What are the signs you need ductwork cleaning sooner than your scheduled inspection?

Signs include visible contamination such as mould growth or vermin, a heavy build-up of dust and debris, unexplained health complaints like allergy symptoms or respiratory issues among occupants, neglected filter maintenance, and a change in building use that shifts the space into a higher BS EN 15780 classification.

How do I find out my building's actual duct cleaning interval?

A qualified HVAC technician can classify your system under BS EN 15780 and carry out vacuum testing in line with TR19 Air guidance. This gives a measured contamination reading, which should set your cleaning schedule rather than a fixed calendar date.

How Often Should You Clean Your Air Ducts?

Q: How often should you clean air ducts?

For most commercial buildings, inspect annually and clean when vacuum testing under TR19 Air shows contamination above the threshold for your classification. High-occupancy or specialist environments, such as schools, hospitals, and food production, are typically inspected more frequently because contamination builds faster and the health stakes are higher.

There's no single fixed interval for air duct cleaning — it depends on how contaminated your ductwork actually is, not how many months have passed. What we believe every building does need is an annual inspection as a minimum, carried out in line with TR19 Air guidance, to establish whether cleaning is actually due.

That distinction matters. Cleaning on a fixed calendar (say, "every two years" regardless of use) wastes money in low-risk spaces and under-protects high-risk ones. The standards work the other way round: inspect regularly, clean when contamination crosses a defined threshold.

If you already know it's time to get your ducts cleaned, visit our duct cleaning service page, or our TR19 Air service.

What the standards say about ductwork cleaning

British Standard BS EN 15780 details three classification levels for buildings dependent on the building’s use, which determine how frequently ventilation systems should be inspected. However, there isn't a universally agreed-upon schedule for how frequently air ducts should be cleaned.

Low – for low occupancy rooms, such as storage rooms.
Medium – for higher occupancy rooms, such as offices, hotels, restaurants or schools.
High – for specialist environments, such as treatment areas in hospitals and laboratories.

Air duct cleaning will only be required once the levels of contamination present within the ductwork exceed the defined levels. TR19 Air was significantly revised in March 2026 — see what's changed in the update for the latest requirements.

TR19 Air provides recommendations for how often different parts of the ventilation system should be cleaned. However, the frequency varies depending on factors like the type of building, its use, and the level of contamination.

How often should you clean air ducts?

For most commercial buildings inspect annually, and clean when vacuum testing under TR19 Air shows contamination above the threshold for your classification.

High-occupancy or specialist environments (schools, hospitals, food production) are typically inspected more frequently because contamination builds faster and the health stakes are much higher due to the presence of more vulnerable groups.

Signs you need ductwork cleaning

Between inspections, these few signs suggest you shouldn't wait for the annual check:

Visible contamination: mould growth inside the ducts, signs of vermin, or a heavy build-up of dust and debris.
Unexplained health complaints: a rise in allergy symptoms or respiratory issues (sore throats, concerns around asthma) among occupants can point to poor indoor air quality, with ductwork as one possible cause.
Neglected filter maintenance: filters that haven't been changed on schedule can become completely blocked, straining the HVAC system and reducing the air change rates, letting pollutants build-up indoors. Eventually, filters can break completely under this stress, allowing unfiltered air to enter the space.
A change in building use: converting a storage area to an occupied office, for example, shifts you into a higher BS EN 15780 classification and a shorter inspection cycle.

For a more thorough breakdown of what to look for between inspections, see 5 Signs You Need to Clean Your Air Ducts.

Keeping air ducts clean between cleans

A few habits keep contamination lower for longer, and reduce how often full cleans are needed:

Regular inspection: don't wait for symptoms; scheduled checks catch build-up before it becomes a problem.
Filter discipline: replace filters on the manufacturer's schedule, not an ad-hoc one. A proactive attitude always beats a reactive one - see our blog on preventative maintenance.
HVAC servicing: a well-maintained system distributes air more evenly and puts less strain on ductwork.
Local guidance: some sectors (healthcare, food production) have additional regulatory requirements on top of TR19 Air, so check what applies to your building. See Duct Cleaning: UK Laws and Guidelines for the general legal position.

Getting an accurate answer: when do I actually need ductwork cleaning?

The only way to know your actual cleaning interval is a proper assessment. A qualified HVAC technician will classify your system under BS EN 15780 and carry out vacuum testing in line with TR19 Air guidance, giving you a contamination reading rather than a guess. This testing is done via EVT (PVT) dust sampling — see our guide for exactly how it works. That reading — not the calendar — is what should set your cleaning schedule.

Talk to an expert

ARM Environments carries out TR19 Air-compliant vacuum testing and ductwork cleaning across commercial and specialist environments. Get in touch for an assessment and a cleaning schedule based on your building's actual contamination levels, not a guess.