Process & access
There is a clear standard for this. TR19 and DW144 set how many access panels ductwork needs, where they go and how they are made - so the whole system can actually be cleaned.
The short answer
How many access panels should ductwork have? The headline figure from TR19 Grease is a minimum of one every two metres, but that is only part of it. Panels also have to be placed at strategic points - changes of direction, dampers, fans and filters - so that every part of the system can be inspected and cleaned. The principle behind the number is simple: there should be enough access, in the right places, that no length of duct is left unreachable. It is a genuine standard, not a matter of opinion.
Where panels go, and how they are placed
Spacing every two metres keeps straight runs reachable, but grease and debris collect at the awkward points - where the duct changes direction, at dampers, and around fans and filters - so panels are required there too. Guidance built on DW144 places panels on both sides of in-line items like dampers and filters, and at least one at each change of direction, precisely because those are the spots a brush cannot pass through blind.
Placement on the duct matters as much as position along it. Panels should be fitted on the side of the duct where possible, at least ten millimetres above the base, to minimise the risk of grease weeping from the joint. The top of the duct is acceptable where a side panel is impractical, and the underside only as a last resort - with a leak-free fit and a notice warning that oil may be released on opening. These placement rules are what stop the access provision itself becoming a source of leaks.
How panels are made, and a useful contrast
The panels themselves have to be made to standard, not improvised. Under DW144 they are made of the same material as the ductwork, insulated and sealed to prevent leaks, and fitted with quick-release catches so they can be opened for every clean without tools. Size is capped: as large as the duct permits up to a maximum of 460mm by 610mm, so the opening never weakens the structure, with the aperture kept free of sharp edges and unobstructed by other services.
It helps to know that grease systems are held to a tighter access standard than general ventilation. Where kitchen extract needs panels at a minimum of every two metres, general ventilation ductwork under the air standard is typically accessed around every fifteen metres - reflecting the far greater fire risk of grease and the need to reach every part of an extract system. So if your kitchen ductwork has only occasional panels spaced like an office air system, it is under-provided for the job it does, and stretches of it cannot be properly cleaned.
Enough access, in the right places, made the right way
The access-panel standard exists so that the whole system can be cleaned, verified and re-cleaned on schedule - not just the parts that happen to open. Enough panels, at the right spacing and strategic points, made and placed to DW144, is what turns ductwork into something maintainable. Checking your provision against that standard is the first step to a clean that actually reaches everything.
Questions
TR19 Grease sets a minimum of one every two metres, plus panels at strategic points - changes of direction, dampers, fans and filters - so every part of the system can be reached and cleaned.
On the side of the duct where possible, at least ten millimetres above the base to reduce grease leakage. The top is acceptable if a side panel is impractical, and the underside only as a last resort with a warning notice.
As large as the duct permits, up to a maximum of 460mm by 610mm, so the opening does not weaken the structure. The aperture must be free of sharp edges and unobstructed.
Under DW144, the same material as the ductwork, insulated and sealed against leaks, and fitted with quick-release catches so they open for every clean without tools.
Because of the fire risk from grease. Kitchen extract needs access at a minimum of every two metres, whereas general ventilation ductwork is typically accessed around every fifteen metres.
Phoenix Duct Clean · by the numbers
We survey your access provision against TR19 and DW144, and fit compliant panels where they are short - so the whole system can be cleaned and re-cleaned on schedule.