Compliance & responsibility
People want a legal number. The honest answer is that the law does not give one - it gives a duty, and the standard gives the numbers.
The short answer
There is no statute that says 'clean your kitchen extract duct every six months'. The Regulatory Reform (Fire Safety) Order 2005 requires the responsible person to keep fire risk under control, which for a grease system means cleaning it often enough that it never becomes a hazard - a risk-based duty, not a fixed calendar. The numbers everyone quotes come from TR19 Grease, the recognised standard, which translates that duty into benchmark minimum frequencies based on how hard the kitchen works.
Where the numbers come from
TR19 Grease sets minimum cleaning frequencies by usage. A heavy-use kitchen running roughly twelve to sixteen hours a day should have the extract system cleaned about every three months. A moderate-use kitchen at six to twelve hours a day sits at about every six months. A light-use kitchen at two to six hours a day is around every twelve months. These are floors, not targets - a busy operation frying hard all day may need cleaning more often than its category suggests.
The interval is ultimately set by a competent person's cleanliness risk assessment, which weighs cooking type, menu, seasonality and the grease the system actually accumulates - not just the hours on the door. What the standard does fix is that the system must not be left so long that mean grease climbs over 200µm, and that inspection intervals should not exceed twelve months even for the lightest users.
Why the number is not the point
The frequency exists to keep grease below a threshold, so the real test is not the date on the calendar - it is what a technician measures inside the duct. Mean grease across the system must stay below 200µm between cleans; any single reading of 500µm or more calls for immediate localised cleaning; and after a clean, surfaces must verify below 50µm by Deposit Thickness Test or Wet Film Thickness Test. Those are the numbers a fire officer or insurer actually cares about.
This is why treating the interval as a box to tick can still leave you non-compliant. Stretch the schedule and the deposits carbonise, the readings climb, and you breach the standard between visits even though you cleaned 'on time'. Setting the interval from a genuine risk assessment - and shortening it if the readings say so - is what keeps you both lawful and safe.
Getting your interval right
Because the law is risk-based, the compliant answer for your kitchen is specific to your kitchen. A short site survey assesses the cooking, the system and the grease it carries, sets the right cleaning interval, and turns the Fire Safety Order's open-ended duty into a fixed, defensible schedule - with a certificate at each visit to prove you kept to it.
Questions
No. The Fire Safety Order sets a risk-based duty, not a fixed interval. TR19 Grease provides the benchmark frequencies - roughly every 3, 6 or 12 months depending on how heavily the kitchen is used.
TR19 Grease suggests about every three months for kitchens running roughly twelve to sixteen hours a day. That is a minimum; hard-frying operations may need it more often.
A competent person's cleanliness risk assessment, which weighs cooking type, menu and the grease the system genuinely accumulates - not just the hours the kitchen is open.
Yes. If the interval is too long for your grease load, deposits can exceed the thresholds between visits. Compliance is judged on the grease readings, so the schedule has to be set from real risk, not habit.
Inspection intervals should not exceed twelve months even for light users, and mean grease must stay below 200µm between cleans, with any 500µm reading triggering immediate localised cleaning.
Phoenix Duct Clean · by the numbers
A short survey sets the right frequency for your kitchen and the schedule that keeps you compliant.