What the standard fixes
EN 13384 sets out the thermal and fluid dynamic calculation methods for chimneys. In plain terms: given an appliance and given a chimney, it is the procedure that establishes whether the combination works — whether the draught available meets what the appliance requires, and whether the gases stay above the conditions at which they would condense inside the flue.
It is published in parts, one for a chimney serving a single appliance and another for a chimney serving several, because those are different problems.
What goes into it is not on any label: the appliance’s declared flue gas temperature and mass flow, its required draught, the chimney’s effective height, its internal cross-section, its insulation, the connecting pipe’s route and every bend in it, and the conditions outside.
What it does not promise
It does not certify a product. It is a method, and it produces an answer about a combination rather than a property of an object.
It does not survive a change. Replacing an open fire with a closed appliance changes the gas temperature and the mass flow, which is exactly the case where the old chimney was adequate and the new combination is not. The calculation has to be redone, and the fact that the diameters still match is irrelevant.
And it is not something a listing can do for you. No seller knows your chimney’s effective height, its cross-section or its insulation.
The documents that sit beside it
It takes its appliance inputs from the appliance test standards — the flue gas temperature, the mass flow and the required draught are all declared figures produced there. It takes its chimney inputs from the classified products and from the existing structure.
A draught regulator, which this site treats as its own family, exists because the calculation can come out the other way: a chimney that pulls harder than the appliance needs sends heat up the flue and burns fuel faster, and a damper or a regulator is the answer to that rather than to a shortage.
Where it appears on this site
Wherever a page reports a required draught, which is on every appliance family where a maker publishes one, and on every flue family.
It is the clearest example on this site of the boundary the whole method rests on. A page here reports the appliance’s declared figures and the product’s declared classes. Whether the two work together in your building is a calculation somebody competent performs with inputs no listing carries — and the page says that instead of implying an answer.
Questions that keep arriving by post
My stove’s spigot matches my flue. Is that enough?
No. Diameter is one input among many; effective height, cross-section, insulation, the route of the connecting pipe and the appliance’s own declared gas temperature and mass flow are the others. Matching diameters is a necessary condition mistaken for a sufficient one.
I am replacing an open fire with a closed appliance. Does the chimney still work?
It has to be reassessed, because a closed appliance sends gases up cooler and slower than an open fire did. This is the single most common case where an adequate chimney stops being adequate, and it is a calculation rather than a judgement.
Why would a chimney pull too hard?
Because draught comes from the chimney, not from the appliance, and a tall well-insulated shaft can produce more than an appliance needs. The result is fuel burned faster and heat sent up the flue, and it is what the damper and draught regulator families exist for.
Last reviewed 22 September 2026