Phoenix Journal · Extraction
Charcoal grills and wood-fired ovens create a tougher, more flammable deposit than any gas hob - and your extraction system pays the price. Here is why solid fuel cooking is the hardest cleaning challenge of all, and how to stay on top of it.
A charcoal grill or a wood-fired oven does something no gas or induction hob does - it burns solid fuel, and that changes everything that ends up inside your extraction system.
When you cook over charcoal, embers or logs, three things travel up into the canopy and ductwork at once: airborne grease from the food, fine carbon soot from the fuel, and creosote - a sticky, tar-like residue produced when wood smoke condenses on cooler metal surfaces. Gas kitchens really only deal with the first of those. Solid fuel kitchens deal with all three, and the mix bakes onto duct walls at high temperature into a hard, carbonised layer that is far more stubborn than the soft grease film you find above a fryer.
That combination is exactly why the industry treats solid fuel cooking as a special case. The current UK standard, BESA's TR19® Grease specification - released on 15 April 2024 - singles out solid fuel cooking, chargrills and high-temperature wok cooking as operations that typically need more frequent inspection and cleaning than a conventional kitchen. It even recognises two different deposit types when it comes to measuring cleanliness: the Wet Film Thickness Test for soft grease and cooking oil, and the Deposit Thickness Test for hard, carbonised deposits - the kind a charcoal grill produces every single service.
So the challenge is not just that these kitchens get dirtier. It is that the soiling is a different substance, sitting in a hotter part of the system, harder to remove, and more likely to catch fire. Understanding that is the first step to keeping the kitchen safe.
TR19® Grease sets baseline cleaning frequencies according to how many hours a day the kitchen runs. Heavy use of 12 to 16 hours a day points to a clean every three months; moderate use of 6 to 12 hours a day to every six months; and light use of 2 to 6 hours a day to every twelve months. Those are the starting points - but for charcoal and wood-fired kitchens they are usually just that, a starting point rather than the answer.
Here is why. In a busy kitchen, grease and carbon can build up in some sections of the extraction system at a rate of up to 2mm per month. TR19® Grease asks you to keep deposits below a mean average of 200 microns between cleans, with any patch of 500 microns or more flagged for spot cleaning. At 2mm a month, a heavily used charcoal grill line can blow through the 200-micron threshold in a matter of weeks, not months. That is why a chargrill or Josper-style oven often justifies monthly or six-weekly inspection even when the calendar says quarterly.
The honest answer is that frequency should be driven by evidence, not by a fixed diary entry. A post-clean deposit reading, a photographic survey of the internal duct surfaces, and a note of how hard the kitchen actually works together tell you the real interval. If you are running solid fuel, assume you sit at the demanding end of the scale until measurement proves otherwise.
Cleaning a solid fuel system properly is a good deal more involved than wiping down a canopy. Because the deposit is hard and carbonised rather than a soft grease film, it usually cannot be dissolved and wiped - it has to be physically broken down and removed from every internal surface, from the canopy and filters right through the ductwork to the extraction fan and discharge point.
A thorough clean to TR19® Grease will typically cover:
The clean is only half the job; the other half is proof. TR19® Grease expects any deposit left behind after cleaning to measure below 50 microns, verified and recorded. A credible contractor will give you before-and-after photographs, deposit readings and a post-clean report that names which sections were reached and which - if any - could not be, along with a recommendation to fit further access. That paperwork is what an insurer or a fire risk assessor will ask to see. Where a wood-fired oven also serves grease-heavy dishes, that carbonised soiling has a lot in common with the stubborn residues we tackle in hotel kitchens with multiple food outlets, where several cooking styles feed one shared extraction route.
The short version is fire. Around 70% of fires in commercial kitchens are linked to the extract ventilation system and the build-up of fat and grease within it. Add solid fuel to that picture and the risk climbs sharply: live embers and flare-ups sit directly beneath a duct lined with flammable carbon and creosote, and a grease fire in the canopy can travel through the ductwork and spread through a building in minutes.
The consequences are not only physical. Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person for the premises has a legal duty to manage fire risk - and a neglected, carbon-caked extraction system is a clear failing that can surface in a fire risk assessment or an environmental health inspection. Just as important, most commercial insurance policies expect the extraction system to be cleaned to a recognised standard on a documented schedule. If it is not, a claim after a fire can be reduced or refused outright, leaving the business to carry the loss.
Keeping on top of it protects far more than the metalwork. A clean system extracts smoke, heat and CO₂ efficiently, keeps the kitchen a tolerable place to work over a hot grill, and gives you the certificate trail that keeps insurers, assessors and inspectors satisfied.
Questions
In almost all cases, yes. Solid fuel produces carbon soot and creosote on top of ordinary cooking grease, and that mix bakes onto duct walls into a hard, flammable layer that accumulates fast. TR19 Grease specifically names solid fuel cooking, chargrills and high-temperature wok cooking as operations that typically need more frequent inspection and cleaning, and busy grill lines often warrant monthly or six-weekly attention rather than the standard quarterly interval.
Compliance is demonstrated through documentation, not just a clean-looking canopy. After a clean to TR19 Grease, remaining deposits should measure below 50 microns, verified and recorded. Ask your contractor for before-and-after photographs, deposit thickness readings and a post-clean report stating which sections were accessed. That evidence is what an insurer, a fire risk assessor or an environmental health officer will expect to see.
Phoenix Duct Clean · by the numbers
The right kit only helps if the system stays clean. Phoenix degreases canopies, filters and ductwork to TR19 Grease - UK-wide, overnight.