Free guide for facilities teams
How to Read a TR19 Ventilation Hygiene Report
A TR19 report should tell you three things clearly: what condition your systems are in, what action is justified, and how you will know the action worked. This guide explains how to check that yours does.
1. What a complete report should contain
- Scope and purpose — why the survey was done (routine, pre-clean, post-clean, complaint, handover) and which systems were included.
- System register — each system identified, with its type, what it serves and where it is.
- Test locations on a plan or schematic — you should be able to find every test point in the building.
- The test method used at each location — and why that method was chosen.
- Individual results — every reading, not just a summary or pass/fail.
- Photographs linked to locations — a photo you can't match to a test point proves very little.
- Classification against TR19 criteria — for each system, not the whole building.
- Inaccessible areas and limitations — what was not inspected, and why.
- Prioritised recommendations — which systems need action, in what order, and which do not.
- Re-inspection or verification advice — when to look again, and how cleaning will be verified.
2. Understanding the results
| Method | What the number means | Watch out for |
|---|---|---|
| Deposit Thickness Test (DTT) | Thickness of dry deposit on the duct surface, in microns (µm), read on site. | DTT is only reliable on suitable flat, rigid metal surfaces with dry deposits. Readings from spiral, lined or greasy ductwork should be questioned. |
| Vacuum test (EVT, formerly PVT) | Mass of dust from a defined template area (typically 100 × 100 mm), in g/m² or mg/m², found by weighing. | Check the sample area, how many samples were taken and that each result traces back to a location. |
| Wet Film Thickness Test (WFTT) | Depth of wet or soft grease, in microns, measured with a comb gauge. | Used for kitchen extract under TR19 Grease — not for dry dust in general ductwork. |
| Visual inspection | Condition, visible deposits, damage and debris. | Useful and necessary, but not a quantitative result on its own. |
Results should be compared with the TR19 criteria for that system type and risk. A single high reading does not always mean a whole system needs cleaning; a single low reading does not prove a system is clean. Look for enough test locations to represent each system — as a rule of thumb, at least three per system, and more for larger or more complex systems.
3. Outcome labels in TR19 Air Version 2
Version 2 formalises post-work reporting. After cleaning, the contractor's Post-Work Verification Report should state one of four outcomes for each system:
| Outcome | What it means for you |
|---|---|
| Full Clean | The whole system was cleaned. Expect before-and-after photos and test results at the same locations. |
| Partial Clean | Only part of the system was cleaned. The report should show exactly which sections, and why the rest was excluded. |
| Inspection (Outcome 'Clean') | The system was inspected and did not need cleaning. |
| Inspection (Outcome 'Not Clean') | The system was inspected and needs cleaning that has not yet been done — this is an open action on your records. |
4. Red flags
- A 'certificate' with no test results, locations or photographs behind it.
- One summary result for the whole building instead of results by system.
- No mention of inaccessible sections — every building has some.
- The same company recommending cleaning, carrying it out and signing it off, with no independent verification.
- DTT readings reported from spiral or lined ductwork with no explanation.
- Post-clean results taken at different locations from the pre-clean results.
- No re-inspection date or verification plan.
5. Questions to ask whoever wrote the report
- Which edition of TR19 did you assess against?
- Why did you choose this test method for each system?
- How did you choose the test locations, and how many per system?
- Which parts of the system could you not access?
- Which systems do not need cleaning — and why?
- How will cleaning be verified, and by whom?
6. What to do next
If the report is clear and complete, use it to plan any cleaning as a defined scope and put the next inspection in your PPM schedule. If it leaves you with questions, or you want a second opinion before committing to cleaning, an independent assessor can review the report or re-test key systems.
About Green Air Monitoring
Green Air Monitoring provides independent ventilation hygiene assessments for commercial buildings. We assess, specify and verify — we never clean.
This guide is general information and does not replace BESA TR19® or professional advice for your building. TR19® is a registered trademark of the Building Engineering Services Association.