Section 2: Additional provisions for soild fuel burning appliances (including solid biofuel) with a rated output up 50kW
Guidance given in this Section should be read in conjunction with guidance given in Section 1.
Guidance on the installation of solid fuel burning appliances is contained in the following standards:
I.S. 258: Domestic Solid Fuel Cookers with Integral Boilers, Part 1:1984 Safety Requirements, Part 2: 1984 General Requirements;
BS 8303 Installation of domestic heating and cooking appliances burning solid mineral fuels: Part 1: 1994 Specification for design of installations, Part 2: 1994 Specification for installing and commissioning on site and Part 3: 1994 Recommendations for design and on site installation;
I.S.EN 15287-1:2007+A1:2010 Chimneys — Design, installation and commissioning of Chimneys Part 1: Chimneys for non-room sealed heating appliances;
I.S.EN 15287-2:2008 Chimneys — Design, installation and commissioning of Chimneys Part 2: Chimneys for room sealed heating appliances.
Air supply to appliances
Any room or space containing an appliance should have a ventilation opening (or openings) of at least the size shown in Table 1. For appliances designed to burn a range of different solid fuels the air supply should be designed to accommodate burning the fuel that produces the highest heating output.
Table HJ1 - Air supply to non-room sealed solid fuel appliances - Extract from TGD J
Flue sizes should be at least:
(a) for connecting flue pipes, equal to that of the flue outlet on the appliance;
(b) for chimneys, at least the size shown in Table 2, but never less than the size of the flue outlet on the appliance or that recommended by the appliance manufacturer.
Specialist advice should be sought when proposing to construct flues having an area of:
more than 15% of the total face area of the fireplace openings; or
more than 120,000 mm2 (0.12m2 ).
Table HJ2 - Size of flues - Extract from TGD J
Height of flues
Flues should be high enough to ensure sufficient draught to clear the products of combustion. The height necessary will depend upon the type of appliance, the height of the building, the type of flue and the number of bends in the flue (see Diagram 2, 3 or 4 as appropriate).
Diagram HJ3 - Outlets from flues for solid fuel burning appliances - Extract from TGD J
Location of flue outlets
The outlet from a flue should be positioned above the roof of a building as shown in Diagram 3. Where flues discharge on or near roofs with surfaces which are readily ignitable, such as thatch or shingle roofs, the clearance between flue and roof should be increased (see Diagram 4).
*Diagram HJ4 - Outlets from flues for solid fuel burning appliances - clearances to readily ignitable roof coverings - Extract from TGD J *
*Direction of flues
Flues should be vertical wherever possible and where a bend is necessary, it should not make an angle of more than 45° with the vertical. Horizontal flue runs should be avoided except in the case of a back outlet appliance, when the length of the horizontal section should not exceed 150 mm unless otherwise specified.
Bends above the flue mouth may help to reduce splashes of rain and soot that may fall on the hearth but the angle of the bend should be no greater than 45° and preferably less than 30°.
The inside surface of the bend should be smooth and there should be no reduction in the area of the flue at the bend.
Connecting flue pipes
A connecting flue pipe should only be used to connect an appliance to a chimney.
Connecting flue pipes may be of any of the following materials complying with the requirements of I.S. EN 1856-2:2009:
(a) Cast iron conforming to material type 00 (Table 2, I.S. EN 1856-2:2009);
(b) Mild steel conforming to material type 01, (Table 2, I.S. EN 1856-2:2009), with a minimum wall thickness of 3 mm;
(c) stainless steel conforming to materials type 40, 50 or 60 (Table 2, I.S. EN 1856- 2:2009) with a minimum wall thickness of 1 mm;
(d) Double sided vitreous enamelled steel flue pipes conforming to material type 80 (Table 2, I.S. EN 1856-2:2009) with a minimum steel wall thickness of 1.2 mm. 2.4.3
Connecting flue pipes with spigot and socket joints should be fitted with the socket uppermost to contain moisture and other condensates in the flue.
Location and shielding
Connecting flue pipes should not pass through any roof space, partition, internal wall or floor, except to pass directly into a chimney through either a wall of the chimney or a floor supporting the chimney. Connecting flue pipes should also be guarded if they could be at risk of damage or if the burn hazard they present to people is not immediately apparent. Uninsulated flue pipes should be separated from combustible material by at least the distances shown in Diagram 5.
Where a connecting flue pipe is connected to a system chimney at the ceiling level a drop of 425 mm of twin wall chimney would provide sufficient shielding to give the required straight-line clearance for the single wall connecting pipe to the ceiling for domestic installations (for further information see HETAS Technical Note HTN004).
Diagram HJ5 - Separating flue pipe from surface of adjacent combustible material - Extract from TGD J
Chimneys for use with solid fuel appliances should be capable of operating at flue gas temperatures of 600o C and of withstanding a sootfire (temperature of 1000° C) without any structural change which would impair the stability or performance of the chimney.
Where a chimney is not directly over an appliance, provision should be made for adequate cleaning and debris removal. Where necessary, a debris collecting space should be provided which is accessible for emptying.
Custom built or built in-situ masonry chimneys should be lined with:
(a) liners meeting the performance level represented by designation T600 N2 D 3 G as defined in I.S. EN 1443:2003.
(i) clay/ceramic flue liners with rebated or socketed joints meeting Class A1N2 or A1N1 as described in I.S. EN 1457: Part 1 2012, (see Table A5) or
(ii) concrete flue liners with rebated or socketed joints meeting Class Type A1 or A2 as described in I.S. EN 1857:2010 (see Table A6);
(b) high alumina cement and kiln burnt or pumice aggregate pipes with rebated or socketed joints or steel collars around joints.
The liners should be fitted with the sockets or rebates uppermost. Liners should be jointed with fire-proof mortar, and any space between the liners and the brick/block work should be filled with a weak 1:1:12 cement/lime/sand mortar or insulating mix such as:
(a) one part ordinary Portland cement to 6 parts Vermiculite, or
(b) one part ordinary Portland cement to 10 parts Perlite, or
(c) one part ordinary Portland cement to 20 parts suitable lightweight expanded clay aggregate minimally wet.
These chimneys should be constructed of factory made components suitable for their intended use. They may incorporate a flue or be lined. Flueblocks suitable for use with solid fuel appliances include:
(a) flueblocks meeting the performance level represented by designation T600 N2 D 3 G as defined in I.S. EN 1443:2003.
(i) clay flueblocks meeting Class FB1 N2 as described in I.S. EN 1806:2006,
(ii) concrete flueblocks meeting Class A1 or A2 as described in I.S. EN 1858:2008 (see Table A6);
(b) flueblocks lined as specified for masonry chimneys in sub-section 2.5.3. and meeting the classification T600 N2 D 3 G as described in I.S. EN1443: 2003.
The thickness of the walls of a brick or blockwork chimney or a flueblock chimney, excluding the thickness of any liner should be at least:
(a) 100 mm thick between one flue and another,
(b) 100 mm thick between a flue and the outside air or between a flue and another part of the same building (but not another part which is a dwelling or is constructed as a separate fire compartment),
(c) 200 mm thick between a flue and another compartment of the same building, another building or another dwelling. This thickness should be carried up to the underside of the roof covering,
(d) 200 mm thick between one flue and another where flues serve appliances located in separate compartments, buildings, or dwellings. This thickness should be carried up to the underside of the roof covering.
Combustible material should be separated from a masonry chimney or a flueblock chimney by at least the following distance:
(a) 200 mm from a flue, or
(b) 40 mm from the outer surface of a chimney or fireplace recess unless it is a floorboard, skirting, dado or picture rail, mantelshelf or architrave. Metal fixings in contact with combustible materials should be at least 50 mm from a flue (see Diagram 6).
Diagram HJ6 - Minimum separation distances from combustible material in or near a chimney - Extract from TGD J
Metal system chimneys
These chimneys should be double-walled insulated chimneys:
(a) constructed in accordance with the recommendations of I.S. EN 1856-1 and meeting the performance levels represented by the designation T600 N1 D 3 G, or T450 N1 W 2 G for wood pellet appliances, or
(b) where a connecting flue with a length of not less than 600 mm meeting the above designation is used the chimney designation may be reduced to T450 N1 D 3 G, and
(c) installed in accordance with the relevant recommendations in I.S. EN 15287- 1:2007.
A metal system chimney should not:
(a) pass through any part of the building forming a separate compartment, unless it is cased in non-combustible material giving at least half the fire resistance of the compartment wall or floor (see Technical Guidance Document B - Fire Safety);
(b) be placed with its outer wall nearer to combustible material than a distance xx, or
(c) pass through a cupboard, storage space or roof space, unless it is surrounded by a non-combustible guard at a distance of at least xx from the outer wall of the chimney.
For (b) and (c) above, the distance xx should be specified by the manufacturer in accordance with I.S. EN 1856-1 (see Diagram 7).
Diagram HJ7 - Relationship of system chimneys to combustible material - Extract from TGD J
The heating appliance should not support the weight of the chimney except when the heating appliance manufacturer states in his instruction that the load bearing capacity is sufficient and where cleaning of the chimney can be undertaken without dismantling.
The liner manufacturer's instructions for supporting the liner should be followed. Where the liners are to be supported on a lintel or foundations at the base of the chimney they should be adequate for the liner load, including any condensate collectors, cleaning and inspection elements, and T-pieces or elbows.
The spacing of supports and unsupported height declared by the manufacturer should not be exceeded. Chimneys in accordance with I.S. EN 1858: 2008 should have a maximum unsupported height of 4.5 times the least cross sectional dimension, but not higher than 3 m.
Rigid or flexible flue liners
Stainless steel rigid or flexible flue liners complying with the appropriate designation of I.S. EN 1856- 2:2009 and meeting the performance level specified in sub-section 2.5.7 may be used in an existing chimney.
Flexible metal flue liners should be installed in one complete length without joints within the chimney. When being installed for a solid fuel appliance in a flue lined chimney it should be sealed at the top and bottom, the space between the chimney and the liner should be filled with an appropriate insulating material, (see sub-section 2.5.3), unless
this is contrary to the manufacturer’s instructions.
Flexible flue liners may not be appropriate for large non-lined chimneys without specialist advice.
Tapered gathers should be provided to fireplaces for open fires. Gathers should be constructed of non-combustible materials. Ways of achieving these gathers include:
(a) using prefabricated gather components built into a fireplace recess, or
(b) corbelling of masonry; or
(c) using a suitable canopy; or
(d) using a prefabricated appliance chamber incorporating a gather.
A solid fuel appliance should be provided with a solid, non-combustible hearth that will prevent the heat of the appliance from igniting combustible materials. A hearth should be either:
(a) a constructional hearth at least 125 mm thick; (see 22.214.171.124) or
(b) a free-standing, solid, non-combustible hearth at least 12 mm thick.(see 126.96.36.199)
The hearth area should be not less than the area shown in Diagram 9 and the appliance itself should be located on the hearth in accordance with Diagram 12 in order to give adequate protection from the risk of ignition of the floor by direct radiation, conduction or falling embers.
A constructional hearth should be provided of solid, non-combustible material, such as concrete or masonry, at least 125 mm thick (which may include the thickness of any solid, non-combustible floor and/or decorative surface) and be at least the sizes shown in Diagram 9.
Combustible material should not be placed under a constructional hearth unless:
it is to support the edges of the hearth, or
there is an air space of at least 50 mm between the material and the underside of the hearth, or
there is a distance of at least 250 mm between the material and the top of the hearth (see Diagram 8).
Diagram HJ8 - Combustible material under hearth - Extract from TGD J
Free standing hearths
A free-standing, solid, non-combustible hearth should only be provided where the appliance will not cause the temperature of the top surface of the hearth on which it stands to be more than 100º C. It should be at least 12 mm thick, and should have a minimum plan area of 840 mm x 840 mm as shown in Diagram 9.
Diagram HJ9 - Hearth sizes - Extract from TGD J*
Fireplace recesses should be constructed of solid non-combustible material to the appropriate size given in Diagram 10.
Diagram HJ10 - Fireplace recesses - Extract from TGD J
Fireplace lining components
A fireplace recess may require protection from the heat of inset open fires, to ensure durability, by the use of fireplace lining components or fire bricks.
Walls adjacent to hearths
Walls adjacent to hearths, which do not form part of a fireplace recess, should be constructed as indicated in Diagram 11 and Diagram 14.
Diagram HJ11 - Wall adjacent to hearth - Extract from TGD J
Location of appliances
(a) should not be placed closer to the edges of a constructional hearth or to any combustible material laid on it, than is shown in Diagram 12, and
(b) should be separated from combustible materials as shown in Diagram 13.
Diagram HJ12 - Placing appliance on a hearth - Extract from TGD J
Diagram HJ13 - Separation appliance from combustible materials in walls - Extract from TGD J
Diagram HJ14 - Wall adjacent to hearths - Extract from TGD J