Duct Doctor · London and the South East
TR19 inspections and grease testing
Grease thickness testing, surveys and TR19® audits that show how much grease is in your kitchen extract and when it needs cleaning.
- Not knowing how much grease is in the duct
- A cleaning interval that’s a guess
- An insurer asking for evidence of cleaning
What tR19 inspections and grease testing involves
You can’t see inside a duct from the kitchen, so the only way to know how much grease is there is to measure it. BESA’s guidance is that grease should not exceed a mean of 200 microns between cleans, and that 500 microns or more at any point needs immediate spot cleaning. Readings are taken by Wet Film Thickness Test (WFTT) or Deposit Thickness Test (DTT) at set points along the system. We carry out grease thickness testing, pre-clean surveys that map the system and its access, post-clean verification to check a clean was done properly, and TR19 audits for insurers. Each one gives you photos, readings and a plain-English report. Readings are what turn BESA’s minimum frequencies into the right interval for your kitchen. Our guide to grease thickness testing explains how it works.
We cover London and the South East, and have done since 2009. We’re a BESCA Vent Hygiene Elite member, cleaning to BESA TR19® Grease, we hold CHAS, SafeContractor and ISO 9001, and we’re fully insured.
Problems we put right
- Not knowing how much grease is in the duct
- A cleaning interval that’s a guess
- An insurer asking for evidence of cleaning
- Doubts about whether the last clean was thorough
- No record of where the access panels are
What we work on
- Wet film thickness tests
- Deposit thickness tests
- Pre-clean surveys
- Post-clean checks
- Insurer audits
- Access surveys
How it works
- We agree what you need: grease testing, a survey, post-clean verification or an audit.
- We trace the system from the canopy to the discharge and note every access point.
- Grease readings are taken by WFTT or DTT at set points, with photos at each one.
- We compare the readings with BESA’s guidance and note any areas that need spot cleaning.
- You get a report with readings, photos, access notes and our recommendation.
What the numbers mean
BESA guidance says grease should not exceed a mean of 200 microns between cleans. If any single point reads 500 microns or more, that spot needs cleaning straight away. A system well under the mean may be able to keep to its interval; one close to it may need cleaning sooner. We explain the readings so you can make the decision.
Setting the right interval
BESA’s minimum frequencies are every 3, 6 or 12 months depending on daily hours of cooking. They are minimums. A competent person’s risk assessment, based on grease measurement, sets the real interval. Regular readings show how fast your system fouls, so you clean when it’s needed rather than guessing. A change of menu, longer opening hours or new equipment can all change the picture.
Checking someone else’s work
If you’re not sure the last clean covered the whole system, post-clean verification gives you an independent look. We take our own readings and photos, compare them with the certificate and report you were given, and set out what we find, plainly and fairly. If sections were missed or can’t be reached, you’ll know exactly which ones and why.
Why it’s worth doing now
Cleaning on a guess means you either pay for cleans you don’t need yet or leave grease building up past a safe level. Readings remove the guesswork. They also give you evidence: insurers may ask how you decided your cleaning interval, and a report with readings answers that. If you’ve taken over a site, changed your menu or opening hours, or don’t trust the last certificate, testing now tells you exactly where you stand, and gives you a baseline for every clean that follows.
What affects the quote
We don’t publish set prices, because no two systems are the same. Send us a few details and photos, or book a survey, and we’ll give you a fixed price before any work starts. The main things that change it are:
- The size of the system: number of canopies, length of ductwork, risers and fans
- How much grease or dirt has built up since the last clean
- Access: roof-level fans, ceiling voids, risers and how many access panels there are
- When the work can happen: overnight, weekends or school holidays
- Whether extras are needed, such as new access panels, filter exchange or damper testing
- How many sites you want covered on one schedule
What a good quote includes
- A survey or clear photos before the price is given
- Exactly which parts of the system will be cleaned or tested
- How areas that can't be reached will be recorded
- A certificate or written report with before-and-after photos
- Proof of insurance and accreditations you can check
- The recommended date for the next visit
Afterwards
Your report gives readings at each point, photos, access notes and a recommended next step, whether that’s a clean, a spot clean or another test date. Keep it with your fire safety records and TR19 certificates. Repeat the readings at the interval we suggest so you can see the trend. If cleaning is needed, we can quote for it from the same survey.
TR19 inspections and grease testing: common questions
What is grease thickness testing?
Measuring the depth of grease inside the extract system at set points, by Wet Film Thickness Test (WFTT) or Deposit Thickness Test (DTT). It shows whether the system needs cleaning.
What grease level means the duct needs cleaning?
BESA guidance says the mean should not exceed 200 microns between cleans, and 500 microns or more at any point needs immediate spot cleaning.
Can testing replace regular cleaning?
No. Testing tells you when cleaning is needed and helps set the interval. BESA’s frequencies are minimums, so testing can show you need cleaning sooner, not that you can skip it.
Can you check work done by another contractor?
Yes. Post-clean verification checks the system against the certificate and report you were given.
Do you do audits for insurers?
We carry out TR19 audits that give you evidence of the system’s condition, readings and photos to share with your insurer. We don’t work on behalf of any insurer.
Is a survey needed before every clean?
Every job is surveyed first, from photos and details or a site visit. A full pre-clean survey with readings is useful for first cleans, large systems and sites with access problems.
Do you give a fixed price before you start?
Yes. Send a few details and photos, or book a survey, and we’ll give you a fixed quote, usually within one working day.
Do you work out of hours?
Yes. We work evenings, overnight and at weekends so your kitchen or building doesn’t lose a day, and there’s a 24/7 line for emergencies.
Page updated 30 October 2026
Near you
We cover London and the South East. Find tR19 inspections and grease testing in your town:
- London
- Brighton
- Southampton
- Portsmouth
- Reading
- Oxford
- Milton Keynes
- Guildford
- Chelmsford
- Maidstone
- Woking
- Crawley
- Croydon
- St Albans
- Canterbury
- Basingstoke
- Slough
- High Wycombe