Phoenix Journal · Ductwork
A quoted cleaning frequency should come from measured grease readings, not a sales calendar. Here is how to tell the difference and buy on evidence.
Kitchen extract cleaning
If a contractor quotes you a fixed cleaning frequency before they have ever looked inside your ductwork, you are being sold a schedule, not a survey.
Kitchen extract cleaning is one of the easiest services to oversell, because the numbers sound reassuring and the risk - a grease fire in a hidden duct - is genuinely serious. But the current UK standard is built around evidence, not guesswork. Once you understand what that evidence looks like, you can tell the difference between a frequency that protects you and one that simply protects a contractor's recurring revenue. This guide walks you through the questions to ask, the readings to demand, and the tactics that should make you pause before you sign.
Overselling almost always hides in the gap between what sounds sensible and what has actually been measured. Run any quote through these lists before you commit to a rolling contract.
The reference point for commercial kitchens in the UK is TR19® Grease, the specification published by the Building Engineering Services Association (BESA) for managing fire risk in kitchen extract systems. It is worth knowing what the standard actually says, because a lot of overselling relies on customers half-remembering it.
TR19® Grease does offer indicative starting points based on how hard a kitchen works: heavy use of roughly 12 to 16 hours a day suggests cleaning around every three months; moderate use of 6 to 12 hours suggests around every six months; and light use of 2 to 6 hours suggests around every twelve months. Those bands are useful, and an honest contractor will tell you which one you fall into. The catch is that they are a starting point, not a verdict. Since the 2019 revision, the standard has leaned firmly towards a risk-based approach, where the real driver of frequency is measured grease loading, not a table read in isolation.
That measurement matters because two kitchens in the same band can behave completely differently. A pub kitchen that flame-grills and deep-fries all day lays down grease far faster than a cafe doing paninis and soup for the same hours. Menu, cooking method, filtration and airflow all change the picture. This is exactly why poor ventilation can quietly push your cleaning frequency up - if the system is not moving air properly, grease condenses and settles more heavily, and a genuine survey will show it. A contractor who never measures cannot tell you any of this, so they default to selling you the safest-sounding, most frequent option they can justify.
Grease deposits are measured in microns - a micron is a thousandth of a millimetre - using a Wet Film Thickness Test or a Deposit Thickness Test at points along the ductwork. A cleaned system should come back below 50 microns, which is roughly half the thickness of a human hair. As deposits build back up towards a mean of around 200 microns, the fire risk rises and another clean is due. Those two figures - 50 microns as the post-clean target and about 200 microns as the trigger - are the honest backbone of any frequency conversation.
Here is the practical point. If your last clean brought a section down to clean and the grease came back to 200 microns in four months, quarterly makes sense for that section. If it took ten months to get there, you are almost certainly being oversold if someone insists on quarterly visits. The readings do the arguing for you. This is also why the paperwork matters so much: a proper post-clean verification report, issued within about 30 days, should record what was cleaned, the pre-clean readings, and the recommended next interval based on those readings. That report is the thing your insurer will want to see.
Insurers do take this seriously. Many UK policies expect kitchen extract systems to be cleaned to a recognised standard, and some insurers - Aviva among them - will look for evidence that a competent, standard-compliant provider carried out the work. That is a legitimate reason to keep good records. It is not a licence to be frightened into over-cleaning.
The distinction is simple. Your insurer wants proof that the system is being kept below the risk threshold and that the work is properly documented. They are not usually mandating a specific number of visits detached from evidence. If a contractor tells you your policy "requires" monthly cleaning without pointing to anything in your actual policy wording, treat that as a sales line and check it. The same logic runs the other way, too - thin or vague paperwork is why compliance certificates get questioned by insurers, so the goal is the right frequency backed by clear evidence, not simply the highest frequency you can be talked into.
You do not need to become a ductwork expert to avoid being oversold. You need a sequence. Start with a survey and grease readings, not a schedule. Get the usage band confirmed and the actual microns recorded. Agree a frequency that matches the evidence, with a written commitment to re-measure and adjust rather than lock you in forever. Then keep every post-clean report on file for your insurer and your fire risk assessment. If a provider is happy to work that way, they are selling you protection. If they resist measuring, or bristle when you ask to see numbers, that tells you what the contract is really designed to protect.
Done properly, this often saves money as well as arguments. Some kitchens genuinely need frequent attention, and for those the readings will prove it and justify the spend. Others discover that a heavy default schedule was never warranted, and that a longer, evidence-led interval keeps them just as safe and just as compliant. Either way, the decision is yours to make on facts rather than pressure.
Questions
No, there is no fixed legal interval that says every kitchen must be cleaned quarterly. UK fire safety law requires you to manage the risk, and the recognised way to do that is TR19® Grease, which sets frequency by measured grease loading and usage rather than a single mandated number. Quarterly suits some heavy-use kitchens, but for others it is more often than the evidence justifies.
It should be based on a survey with grease readings taken in microns using a Wet Film Thickness Test or Deposit Thickness Test, combined with your usage band under TR19® Grease. A cleaned system should read below 50 microns, and cleaning is generally due again as deposits approach a mean of around 200 microns. How quickly you reach that threshold is what sets your real interval.
The usage bands give indicative starting points - roughly three-monthly for heavy use, six-monthly for moderate use and yearly for light use. A risk-based frequency, which the standard has favoured since 2019, then adjusts that starting point using your actual measured grease readings. Two kitchens in the same band can need very different intervals depending on menu, cooking method and airflow.
Insurers usually require evidence that the system is kept to a recognised standard and properly documented, rather than dictating a specific number of visits. Some, such as Aviva, expect a competent, standard-compliant provider and a valid post-clean verification report. If a contractor claims your policy demands a set frequency, ask them to point to the exact wording in your policy before you accept it.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.