Safe Distances to Combustible Materials

Due to the levels of heat emitted from flue pipes and stoves, it is essential these are installed at a safe distance from any combustible material which could catch on fire from heat transfer (typically wood, carpets and soft furnishings).

Commonly referred to as 'clearance or distance to combustibles', this measurement varies from Single Wall pipe to Twin Wall flue and from stove to stove. Approved document J of the Building Regulations does get involved here but it is also down to what distances the manufacturer has had the pipe or stove tested to.

It is not uncommon to have to amend your original plans for where you wish your stove and flue to be installed once safe distances to combustible materials are taken into consideration however, they are solely designed to keep you and your home safe as heat transfer into wood can go unnoticed until combustion.

Single Wall Stove Pipe (Vitreous Enamelled)

As Single Wall stove pipes have no insulating material, they transfer a lot of their heat to the outer surface which can become incredibly hot. Therefore, it stands to reason that to be safe you must maintain quite a substantial distance between these pipes and any combustible materials. Building Regulations state this clearance must be at least 3 x the internal diameter of the flue pipe as illustrated below. However, if there are only non-combustible materials close by the flue or you have shielded it with fire proof boarding such as our Vermiculite Fire Boards, then this distance can be reduced to only 1.5 x the internal diameter of the flue pipe.

For example, a 5" (125mm) internal diameter single wall pipe must have a safe clearance from combustible materials of 15" (3 x 5"). This can be reduced to 7.5" (1.5 x 5") to non-combustible materials.

Twin Wall Insulated Flue

Due to the layer of insulation between the inner and outer skins of a Twin Wall insulated flue pipe, the heat emitted from these is greatly reduced and therefore they can be positioned closer to combustible materials. For our Shieldmaster Twin Wall, you only need to maintain a 60mm clearance all the way around the pipe and for SFL Sflue, it is a reduced 50mm distance. In reality, this means the size of hole you would need to cut in a combustible wall or roof for 125mm Shieldmaster Twin Wall would be 295mm across (175mm outer diameter + 60mm + 60mm).

This figure is included within the designation number applicable to your brand of Twin Wall pipes. There is no regulation for the distance of Twin Wall flue pipes to a non-combustible material.

Stoves

Stoves require the greatest clearance to any potentially combustible material but this does come down to the individual brand and model of appliance and is stated on the data plate attached to the stove. This measurement could be in the region of 600mm, 800mm or even greater and may be different for the sides and rear. It is worth noting, most stove manufacturers do not test for clearances to combustibles above the stove and there is no regulation for the distance of a stove to a non-combustible material, only clearances recommended by the manufacturer (usually in the region of 100-150mm to allow air to pass around the unit).

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18th February 2015

Comments

Gavin Jones says:
30th October 2021 at 7:09 am
Can 904 L be used within a timber stud partition? Thanks

Andrew Shuttleworth says:
9th November 2021 at 3:06 pm
When installing a flue near timber, you are required to use insulated Twin Wall flue to reduce heat transfer and the risk of fire. https://www.glowing-embers.co.uk/twin-wall-insulated-flue-systems

Tim Ord says:
5th July 2022 at 12:39 pm
The Stove we are about to have installed has a manufacturers suggested clearances to combustibles of 52cm to the side and 10cm to the rear. We are hoping to have decorative logs in a recess in a non-combustible wall, so the logs will be 10cm to the rear and 16cm to the side (so approx 19cm diagonally to the rear corner). Would this be permissible? Not having much luck getting an answer from Wiking (Miro 1 Stove). Thanks, Tim.

Andrew Shuttleworth says:
6th July 2022 at 11:59 am
The stove manufacturer’s guide must be adhered to, to ensure a safe installation. As they advise a minimum clearance of 52cm to the sides of the stove, I would suggest not placing logs within this area. Should you have any concern about your installation, always consult your HETAS installer.

Bill Clark says:
1st November 2022 at 9:06 pm
I am planning a 5KW wood burning stove with a 6 inch TW external Flue leaving the stove at 45 degrees and passing through my timber framed wall into a 135 tee. The vertical studs are 4? x 2? at 600mm Crs. I plan to use a Ignis insulation system (Part Number 149530). The stove is approx 500mm high and 450mm wide. I will remove the pasterboard between the two studs which are at 600mm and replace with 12.5mm Cement Board. Other voids will be filled with100mm A1 rated Rockwool slabs. Should I be concerned about the two 4 x 2`s? albeit they will be covered by the cement boards (Would two thicknesses of the board be a solution?? Regards Bill Clark