Frequently Asked Questions About Duct Cleaning and TR 19® Compliance

What is TR 19® Air, and how does it differ from TR19® Grease?

TR 19® Air is BESA's specification for internal cleanliness and hygiene management of general ventilation systems, addressing indoor air quality in buildings such as offices, schools, hospitals, and commercial spaces. It was updated in 2023 and released in April 2024 to focus specifically on air quality and occupant health following the COVID-19 pandemic. TR19® Grease is a separate, standalone specification produced in 2019 for fire risk management of grease accumulation within kitchen extraction systems. While both standards address duct cleanliness, TR 19® Air focuses on health and well-being in general ventilation, whereas TR19® Grease specifically addresses fire safety in commercial kitchens.

What is BS EN 15780, and how does it relate to TR 19®?

BS EN 15780 is the British and European Standard for cleanliness of ventilation systems, introduced in 2011 and updated in 2025. It specifies general requirements and procedures for assessing and maintaining ductwork cleanliness, including cleanliness quality classification, assessment methods, cleaning selection, and validation of cleaning effectiveness. TR 19® incorporates and aligns with BS EN 15780 classifications. The British Standard cross-references with other HVAC standards and applies across Europe, while TR 19® remains the UK's widely recognised practical guide that insurance companies and facilities managers commonly reference for compliance.

What are the three cleanliness quality classes in BS EN 15780?

BS EN 15780 defines three cleanliness quality classes based on building use and occupancy. Low risk applies to rooms with only intermittent occupancy, such as storage rooms and technical rooms. Medium risk covers higher occupancy spaces, including offices, hotels, restaurants, schools, theatres, residential homes, shopping areas, and general areas in hospitals. High-risk environments include laboratories, treatment areas in hospitals, high-quality offices, and specialist facilities where air quality is critical. These classifications determine appropriate inspection frequencies and acceptable dust deposit levels for each system type.

What are the acceptable dust deposit levels for general ventilation systems?

According to BS EN 15780 and TR 19® Air, dust levels in medium risk buildings (such as offices, hotels, restaurants, and schools) should be less than 3.0 grams per square metre. For recirculation and secondary ductwork in these buildings, the threshold rises to 4.5 grams per square metre or less. Using the Deposit Thickness Test method, supply and recirculation systems historically required cleaning when deposits exceeded 60 microns, while extract systems had a threshold of 180 microns. These levels have been aligned with BS EN 15780 cleanliness quality classes to provide clear, measurable standards for compliance.

How often should general ventilation systems be inspected?

BS EN 15780 defines risk assessment survey frequencies that form the basis of good ventilation management. For most facilities, inspections should be conducted every two years as a minimum. Higher risk environments such as healthcare facilities, laboratories, and cleanrooms require annual inspections. TR 19® recommends that inspections should not exceed 12-month intervals for any system. The actual cleaning frequency depends on inspection results, deposit thickness measurements, system usage, and the building's cleanliness quality class. Regular assessment ensures systems are cleaned before contamination reaches dangerous or inefficient levels.

What cleaning methods are approved under TR 19®?

TR 19® recognises several approved cleaning techniques that must be selected based on system type, contamination level, and accessibility. Manual scraping removes thick grease deposits, particularly in kitchen systems. Vacuum cleaning with HEPA-filtered units removes dry dust in general air systems. Compressed air agitation breaks up dust before collection and often works with brushing or vacuuming. Chemical applications target grease or biological contaminants, followed by thorough rinsing. Rotary brushing systems scrub internal duct surfaces and suit inaccessible duct runs. The selected method must return all internal surfaces to the cleanliness level defined by TR19® tables showing maximum deposit thicknesses.

What is the Deposit Thickness Test, and why is it important?

The Deposit Thickness Test (DTT) is a measurement method that determines the mean surface deposit thickness in microns on duct internal surfaces. It provides quantifiable evidence of contamination levels both before and after cleaning. The DTT is critical for verifying compliance with TR 19® and BS EN 15780 standards because it gives objective, measurable data rather than subjective visual assessment. Testing is conducted at multiple points within the ductwork system to calculate average deposit levels. Results determine whether cleaning is required and provide documented proof that cleaning has achieved the required standard for insurance and regulatory compliance.

What is the Preferred Vacuum Test?

The Preferred Vacuum Test (PVT) is a development of the vacuum test and forms part of BS EN 15780. It measures dust deposits by weight (grams per square metre) rather than thickness. The PVT is particularly useful for newly installed systems and provides ultimate confirmation of ductwork cleanliness. It works by vacuuming a defined surface area through a filter, which is then weighed to determine deposit levels. The test results can be compared against the cleanliness quality class thresholds to verify whether the system meets the required standard. Both DTT and PVT methods are recognised under TR 19® for different assessment purposes.

Why is access to ductwork so critical for TR 19® compliance?

Without adequate access, thorough inspection and effective cleaning of ductwork is impossible, leaving hidden contamination that compromises air quality, fire safety, and system efficiency. TR 19® requires designers to ensure adequate access both through building fabric and into the system to make planned preventative maintenance practicable. BS EN 12097 specifies requirements for dimensions, shape, and location of access panels for cleaning and service in ductwork systems. Access panels must be of sufficient number, quality, and size to enable unrestricted access to all internal surfaces and in-line components. Designers should seek guidance from specialist cleaning contractors at the design stage to ensure proper access provision.

What must a post-clean verification report include?

A comprehensive post-clean verification report must include photographic evidence taken before and after cleaning from identical positions, Deposit Thickness Test or Preferred Vacuum Test measurements showing pre- and post-clean results, a site plan or system layout showing all cleaned areas, details about access points used and any areas that remain unavailable, a written summary of works completed, notes on any access limitations or recommendations for system improvements, and a hygiene certificate stating the cleaning date, system type, location, and contractor details. This documentation demonstrates compliance with fire regulations, insurance requirements, and internal maintenance policies, providing traceable proof that systems meet recognised cleanliness standards.

What are the health risks of poorly maintained ventilation systems?

Accumulated dust, bacteria, mould spores, and allergens in poorly maintained ductwork recirculate through buildings, causing respiratory issues, allergies, headaches, and fatigue among occupants. Research following the COVID-19 pandemic highlighted the critical role of clean ventilation in preventing airborne pathogen transmission. Poor indoor air quality leads to increased employee absenteeism, reduced productivity, and higher rates of both short-term and long-term illnesses. The impact on health and well-being is now recognised in BS 40102-1:2023, the British Standard for Health and Wellbeing in Buildings, which provides recommendations for measuring and monitoring indoor environmental quality, including ventilation hygiene.

How does duct cleaning affect energy efficiency?

Accumulated debris in air ducts impedes airflow, forcing fans to work significantly harder to maintain required ventilation rates. This results in increased energy consumption, higher operational costs, and premature wear and tear on system components. Regular cleaning enhances system efficiency, leading to measurable energy savings and prolonged equipment lifespan. This is particularly relevant for retrofitting buildings to achieve net-zero emissions targets. Clean ductwork also reduces pressure drop across the system, allowing fans to operate at lower speeds while maintaining performance. The energy savings from proper duct maintenance typically offset cleaning costs within a short period.

Are TR 19® standards legally required?

TR 19® and BS EN 15780 are not statutory legal requirements in themselves, but they represent widely accepted industry best practice. Employers and building managers have legal obligations under the Health and Safety at Work Act and Occupiers Liability Act to ensure working environments are safe and healthy, which includes maintaining acceptable air quality. The Regulatory Reform (Fire Safety) Order 2005 requires assessment and reduction of fire risks, including in ventilation systems. Courts would view non-compliance with such widely accepted standards dimly. Insurance companies frequently require adherence to TR 19® standards, and failure to comply can invalidate policies and result in denied claims following incidents.

How do I find a TR 19® compliant contractor?

Look for contractors registered with the Vent Hygiene Register (VHR), which lists contractors certified in TR 19® standards. Verify the contractor holds Professional Indemnity Insurance as stipulated by TR 19® regulations. Check that their technicians have appropriate BESA training and qualifications for the specific work required (GHT qualification for grease systems, air hygiene certification for general ventilation). Request examples of previous verification reports showing photographic evidence, deposit thickness measurements, and proper certification. Ensure they can provide comprehensive documentation, including before-and-after photos, test results, system drawings, and hygiene certificates. Members of professional bodies and certification schemes provide additional assurance of competence and standards compliance.

What happens during a TR 19® inspection?

A TR 19® inspection begins with a visual examination using borescopes or video inspection equipment to assess internal duct conditions. The inspector conducts Deposit Thickness Tests or Preferred Vacuum Tests at representative locations throughout the system to measure contamination levels. They check access panel provision and condition, verify system drawings against actual installation, assess moisture presence and potential microbial growth, examine AHU components including filters and coils, and identify any damage or deterioration. Results are documented with photographs and measurements, then compared against cleanliness quality class thresholds. The inspector provides recommendations for cleaning frequency, access improvements, and any immediate remedial actions required.

Can new ductwork systems be handed over without cleaning?

No. A common misconception before BS EN 15780 was that protection of ductwork on a construction site would guarantee internal cleanliness in newly installed systems. This is incorrect. Construction dust, debris from cutting and joining, and contamination from handling mean that newly installed ductwork rarely meets cleanliness standards without specialist cleaning. BS EN 15780 clarified that where specific confirmation of internal cleanliness is required, designers must specify inclusion of a specialist cleaning contractor from the outset of a contract to internally clean newly installed ductwork before handover. The Preferred Vacuum Test verifies that new systems meet the specified cleanliness quality class.