Some excellent documents by the British Chimney Manufacturer’s Association on this page (really worth a look as easy to read with lots of diagrams) here.
The manual is designed to be used alongside Document J of the Building Regulations England & Wales (stoves without boilers) and Document G of the Building Regulations England & Wales (stoves with boilers) coupled with any advice provided by your local Building Control. Note that regulations for Scotland and Northern Ireland differ slightly and precise details should be checked for compliance. Other regulations may be applicable (e.g. for electrics if adding controls to wet systems). In all cases you should not rely on this manual alone.
1. If the top of the chimney is within 600mm (60cm) of the ridge it should finish 60cm higher than the ridge. We also have the “2.3m rule”. These rules helps ensure draft is not spoiled by wind-induced turbulence.
2. Look at the top of your chimney (where the smoke comes out). Imagine an imaginary horizontal line extending 2.3m in all directions. Nothing should prevent that horizontal line extending to the full 2.3m. This rules helps ensure draft is not spoiled by wind-induced turbulence.
3. As a guide a chimney that is 4.5m high (from top of stove to top of pot) should be high enough to ensure the stove has sufficient draft. With a modern twin wall system you should get away with 3.5m or even 3m if you have to (e.g. out of a shed or caravan or boat).
4. If you have a window anywhere near then check out the regulations (ADJ diagram 17).
5. There must be no bends greater than 45 degrees and there must be no more than four bends in the chimney. If you are using four bends then you must have a soot door between the second and third bend (Building Regs). Note that a “T” off the rear of the stove is classed as two bends (2×45=90).
PLEASE READ ADJ (Document J of the building regulations) PAGES 30 AND 31. READ PAGE 32 ONLY F YOU HAVE AN EASILY COMBUSTIBLE ROOF E.G. THATCHED).
A chimney flue should never be less than 5″ diameter and only certain stoves can use them (DEFRA-approved stoves that allow a 5″ flue can be attached to this diameter flue). Many require a 6″ flue. Some require larger diameter flues. Manufacturer’s instructions may override this and demand a larger diameter than Building regulations ask for.
If a stove requires a flue of a certain diameter you should never connect it to a chimney that has any section with a diameter less than this.
If the stove is DEFRA APPROVED* with a 5″ collar and the stove manufacturer does not state otherwise* then a 5″ liner can be fitted.
** The best way to check this is to download the manufacturer’s fitting instructions from the Internet. This is the document delivered with the stove and the document that a Building Control officer will likely peruse.
To reduce the diameter of a chimney you can line it with a stainless steel “flexi” (a stove will perform best if the flue diameter of the chimney is as close as possible to that of the stove). One might also use a chimney liner because a brick or stone chimney does not pass a smoke test as required by Building Regulations.
Please read CHIMNEYS AND LINERS>flexi lining first, followed by CHIMNEYS AND LINERS> concrete & composite.
A flexible stainless steel liner should only be used within a structurally sound chimney. It should not be joined along its length (you should not join multiple pieces together to make a length).
Building regs allow you to connect your stove directly to a chimney using the methods they suggest. We look at this in more detail in THE STOVE FIT DIRECT TO CHIMNEY.
You can create your own chimney using HT flue pipe (also known as twin-wall flue pipe). See THE STOVE FIT TO FLEXI OR HT.
TOP TIP>>> Not bought a stove yet and running the new chimney outside the building? Consider one with the potential to add a direct air supply (sometimes called “external air supply”). Why? Modern stoves have less hot air leaving up the chimney than older stove-models and however well a modern twin wall system is insulated these external chimneys are invariably colder than internal designs. Usually there is no problem at all but if you ever have a problem with the draw of your stove (poor performance or smoke puffing from stove into room) it is usually because something is causing air to be sucked from the room where the stove is situated causing a vacuum (e.g. another open fireplace in adjoining room or even a tall staircase and trickle vents upstairs) and this is overpowering the draw of the new stove and chimney. Should this fairly rare situation ever arise it is usually curable by connecting the stove’s air intake directly to outside. I have known installers have to remove a stove to change for one with external air capability – how they wish they had chosen one in advance! Installing an external air connection as a matter of course is not a bad idea as one never knows if this problem will affect you or not.