Rules for wood burning stoves: Distance to combustibles

Rules for wood burners exist for a reason

Rules for wood burning stoves

It’s worth following the rules for wood burning stoves. If you have not used or owned a stove before you might not be aware quite how hot the stove and the flue pipe can get. In normal operation a flue pipe will be at 150 to 250 degrees centigrade but can go a lot higher. If deposits attached to the inside of a flue catch fire then a flue pipe can even glow red (worst case scenario). Building regulations must sensibly cover all eventualities (including a pipe glowing red hot) to protect property and life.

A combustible material is any material that is not A1 fire-rated or to as high a specification as this. Plasterboard is officially a combustible material (can though depend on who is signing the project off so ask them). Materials such as “pink plasterboard” might have increased levels of fire resistance but this does not make them A1 fire-rated (e.g. pink plasterboard might be rated as holding back fire for “x” minutes but this is not the same as A1 fire-rated). A1 fire-rated means that it will not catch fire, full stop and it will not fall part under fire. You are safe with brick, stone and plaster as these are non-combustible materials.

Stud walls might have wooden battens behind the plasterboard and in this instance normal Building Regulations for combustible rules should follow.

At the end of the day “who is inspecting the job?” is the real question and it is them that needs to be kept happy.

To make your job very easy just ensure there are no combustible materials anywhere near your stove!

The stove

Your stove must be a minimum distance away from combustible materials. This distance will be specified by the stove manufacturer in their installation instructions (contact them if stove not yet purchased). The distances will often be 24″ or more (if you have an inglenook with any combustibles present then it better be a large one). Remember this is to combustible materials.

See Vlaze shield at foot of this article.

Steel flue pipe (vitreous pipe)

Click for clearer graphic

Steel flue pipe (often called vitreous pipe) is the pipe that comes out of the top of the top or rear of the majority of stoves.

Flue pipes GET EXTREMELY HOT and should be located as to avoid igniting combustible materials. See clause 2.15 and diagram 19 of ADJ (Document J of the Building Regulations).

The key rule for all flue pipe is that any combustible material must be three times “X” away from the flue pipe where X = the diameter of the flue pipe. This means that your 5″ flue pipe should be 15″ away from combustibles and your 6″ flue pipe should be 18″ away from combustibles in any direction.

This distance can be halved if you shield the combustible material. The shield must, of course, be non-combustible (do not use plasterboard as it is not A1 fire-rated and may gradually crumble). There must also be an air gap between the shield and the combustible material of a minimum of 12mm.

Twin wall flue pipe

Twin wall pipe used, instead of vitreous steel pipe, to shield this beam.

Twin Wall flue pipe has a diameter of approx. 2″ more than steel stove pipe due to it being insulated (so a 6″ diameter vitreous would be an 8″ Twin Wall). It is usually used to pass through ceilings and lofts or run outside of buildings (it is often stainless steel but is also available in black).

Twin Wall flue, because it is insulated, only has to be a minimum Xcm from combustibles. “X” is usually 5cm, 6cm or 7cm depending on supplier so please check. Duraflue Easy Fit needs to be 7cm from combustibles. Twin Wall Flue can therefore be used in place of the usual steel stove pipe in areas where a combustible material is close by. More often than not it is used in place of steel in order to protect wooden beams or surrounds.

In order to bypass a wooden beam one requires, from the bottom up: short length steel vitreous pipe (usually 25cm length), vitreous to twin wall adaptor, length of twin wall (usually a metre), twin wall to flue liner adaptor, chimney liner. One can choose to go straight to the stove with the twin wall and one would then just omit the short length of vitreous pipe.

Shielding of steel flue pipe (vitreous pipe)

It is possible to shield a wooden beam from the heat from a steel stove pipe. As can be seen from the regulations outlined above shielding can reduce the minimum allowed distance between pipe and material to 1.5 X diameter rather than 3 X diameter (5″ pipe can now be 7.5″ away and 6″ pipe can be 9″ away).

As a fitter I have one problem with this… I correct myself… the customer usually has one problem with this. As can be seen from the pic below (pic: shield), in order to achieve what is desired, the shield always has to drop below the wooden beam in order to be effective. This means the shield can be seen from the room, especially when sitting on the sofa. The amount that is usually showing is 2 to 5″. I usually have to inform customers that they have no choice in the matter.

In the scribble above the long red arrow (distance from flue to wood) must be a minimum 15″ (5″ diameter flue) or 18″ (6″ diameter flue). The short arrows show an area where the gap should be half of this (7.5″ or 9″). The gap between shield and combustible material must be 12mm minimum.

In the example below, if the steel flue is 5″, then the two long red arrows should be 15″ or more whilst the short red arrows should be 7.5″ or more.


Plasterboard and freestanding stoves

Although your twin wall pipe can be as close as 5cm to combustibles (some brands 6cm or 7cm) your steel vitreous pipe, coming off of the stove, has to be a long way away from combustibles (3x its own diameter – so 15″ for a 5″ pipe and 18″ for a 6″ pipe). Also your stove has to be a long way from combustibles (often 24″ or more see stove installation manual or stove brochure). Plasterboard walls are classed as combustible in Building Regulations (although some Building Control Inspectors seem to use common sense and treat it as non-combustible so you could ask whoever is signing off for their advice). See distance to combustibles. You may wish to take your twin wall pipe all the way to the stove if you are having problems in this area (twin wall can look very big and fat on smaller stoves though – not such a problem if 5″ internal is used as outer diameter is 7″).

This distances can be halved if you shield the combustible material. The shield must, of course, be non-combustible (do not use plasterboard as it is not A1 fire-rated and may gradually crumble). There must also be an air gap between the shield and the combustible material of a minimum of 12mm.

Update June 2016: A company called Vlaze have just launched “aesthetically lovely” Vlaze heat shields that sit behind the stove see pic below:


You can also make a similar heat shield from 12mm Hardiebacker board (buy in 1.2m x 0.8m sheets) then paint it with emulsion (same colour as wall or different, your call). If you do follow this route you will need an air gap between the back of the Hardiebacker and the wall – of at least 12mm (use 12mm spacers close to the corners of the Hardiebacker). I use 12mm copper plumbing-pipe sections as spacers and Thunderbolts. Countersink the Thunderbolt heads then fill countersink hole with Decorator’s Caulking).  Check with whoever is signing the stove off if they are happy with this.

Or, if whoever is signing off the stove is happy, you can tile onto the Hardiebacker (search for “tiling behind wood stove” in Google images for ideas). If one were very naughty one could of course tile straight onto the plasterboard as nobody knows what is behind the tiles anyway – plasterboard with tiles on top is completely safe it’s just that plasterboard is not classed as A1 fireproof. Please do think about hidden wooden battens behind the plasterboard if a stud wall as these are classed as combustibles.





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