Air supply to appliances

2.1 A way of meeting the requirement would be to adopt the general guidance given in Section 1, beginning at Paragraph 1.2, in conjunction with the guidance below.

2.2 Any room or space containing an appliance should have a permanent air vent opening 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.

2.3 Some manufacturers may specify even larger areas of permanently open air vents or omit to specify a rated output (for example in the case of a cooker). In these cases, manufacturers’ installation instructions should be followed subject to any minimum ventilation provisions of this Approved Document.

Size of flues

2.4 Fluepipes should have the same diameter or equivalent cross-sectional area as that of the appliance flue outlet and should not be smaller than the size recommended by the appliance manufacturer.

2.5 Flues should be at least the size shown in Table 2 relevant to the particular appliance, and not less than the size of the appliance flue outlet or that recommended by the appliance manufacturer.

2.6 For multi-fuel appliances, the flue should be sized to accommodate burning the fuel that requires the largest flue.

2.7 For fireplaces with openings larger than 500mm x 550mm or fireplaces exposed on two or more sides (such as a fireplace under a canopy or open on both sides of a central chimney breast) a way of showing compliance would be to provide a flue with a cross-sectional area equal to 15 per cent of the total face area of the fireplace opening(s) (see Appendix B). However, specialist advice should be sought when proposing to construct flues having an area of:

a. more than 15 per cent of the total face area of the fireplace openings; or

b. more than 120,000mm² (0.12m²).

Table 1 Air supply to solid fuel appliances

Table 2 Size of flues in chimneys

Height of flues

2.8 Flues should be high enough to ensure sufficient draught to clear the products of combustion. The height necessary for this will depend upon the type of the appliance, the height of the building, the type of flue and the number of bends in it, and an assessment of local wind patterns. However, a minimum flue height of 4.5m could be satisfactory if the guidance in Paragraphs 2.10 to 2.12 is adopted. As an alternative approach, the calculation procedure within BS EN 13384-1:2005 can be
used as the basis for deciding whether a chimney design will provide sufficient draught.

2.9 The height of a flue serving an open fire is measured vertically from the highest point at which air can enter the fireplace to the level at which the flue discharges into the outside air. The highest point of air entry into the fireplace could be the top of the fireplace opening or, for a fire under a canopy, the bottom of the canopy. The height of a flue serving a closed appliance is measured vertically from the appliance outlet.

Outlets from flue

2.10 The outlet from a flue should be above the roof of the building in a position where the products of combustion can discharge freely and will not present a fire hazard, whatever the wind conditions.

2.11 Flue outlet positions which can meet the requirements in common circumstances are shown in Diagram 17. The chimney heights and/ or separations shown may need to be increased in particular cases where wind exposure, surrounding tall buildings, high trees or high ground could have adverse effects on flue draught.

Diagram 17 Flue outlet positions for solid fuel appliances

Diagram 18 Flue outlet positions for solid fuel appliances – clearances to easily ignited roof coverings (Note: This diagram needs to be read in conjunction with Diagram 17)

2.12 A way of meeting the requirements where flues discharge on or in close proximity to roofs with surfaces which are readily ignitable, such as where roofs are covered in thatch or shingles, would be to increase the clearances to flue outlets to those shown in Diagram 18.

Note: Thatched roofs can sometimes be vulnerable to spontaneous combustion caused by heat transferred from flues building up in thick layers of thatch in contact with the chimney. To reduce the risk it is recommended that rigid twin-walled insulated metal flue liners be used within a ventilated (top and bottom) masonry chimney void provided they are adequately supported and not in direct contact with the masonry. Non-metallic chimneys and cast in-situ flue liners can also be used provided the heat transfer to the thatch is assessed in relation to the depth of thatch and risk of spontaneous combustion.

Spark arrestors are not generally recommended as they can be difficult to maintain and may increase the risk of flue blockage and flue fires. Further information and recommendations are contained in Hetas Information Paper 1/007 Chimneys in Thatched Properties.

Connecting fluepipes

2.13 For connecting fluepipes a way of meeting the requirements would be to follow the general guidance in Paragraphs 1.32 and 1.33.

Location and shielding of connecting fluepipes

2.14 Connecting fluepipes should be used only to connect appliances to their chimneys. They 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 fluepipes 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.

2.15 Connecting fluepipes should be located so as to avoid igniting combustible material. Ways of meeting the requirement include minimising horizontal and sloping runs and:

a. following the guidance in Paragraph 1.45 where the connecting fluepipe is a factorymade metal chimney whose performance is at least equal to designation T400 N2 D3 G according to BS EN 1856-1:2003 or BS EN 1856-2:2004, and installed to BS EN 158271; or

b. separation by shielding in accordance with Diagram 19.

Diagram 19 Protecting combustible material from uninsulated fluepipes for solid fuel appliances

Debris collection space

2.16 Where a chimney cannot be cleaned through the appliance, a debris collecting space which is accessible for emptying and suitably sized opening(s) for cleaning should be provided at appropriate locations in the chimney.

Masonry and flueblock chimneys

2.17 Masonry chimneys should be built in accordance with Paragraphs 1.27 and 1.28. Flueblock chimneys should be built in accordance with Paragraphs 1.29 and 1.30. The minimum chimney thickness and distance to combustibles (xxmm) should be no less than the manufacturer’s product declaration (Gxx) based on testing to BS EN 1858:2008 (concrete flue blocks) or BS EN 1806:2006 (clay/ceramic flueblocks). Other masonry chimney products should exceed the minimum thickness indicated in Diagram 20.

Diagram 20 Wall thicknesses for masonry and flueblock chimneys

Separation of combustible material from fireplaces and masonry flues

2.18 Combustible material should not be located where it could be ignited by the heat dissipating through the walls of fireplaces or masonry flues. A way of meeting the requirement would be to follow the guidance in Diagram 21 so that combustible material is at least:

a. 200mm from the inside surface of a flue or fireplace recess; or

b. at least xxmm from a flue product with designated separation distance (Gxx); or

c. 40mm from the outer surface of a masonry chimney or fireplace recess unless it is a floorboard, skirting board, dado or picture rail, mantel-shelf or architrave. Metal fixings in contact with combustible materials should be at least 50mm from the inside surface of a flue.

Factory-made metal chimneys

2.19 A way of meeting the requirements would be to comply with Paragraphs 1.42 to 1.46 in Section 1 (but not Paragraph 1.42(b)). The appropriate designation is given in Table 3.

Table 3 Minimum performance designations for chimney and fluepipe components for use with new solid fuel fired appliances

Lining and relining of flues in chimneys

2.20 Lining or relining flues may be building work and, in any case, such work should be carried out so that the objectives of J2 to J5 are met (see Paragraphs 1.34 and 1.35). Existing flues being re-used should be checked as described in Paragraph 1.36. Ways of meeting the requirements include the use of:

a. liners whose performance is at least equal to that corresponding to the designation T400 N2 D3 G, as described in BS EN 1443:2003, such as:

factory-made flue lining systems manufactured to BS EN 1856-1:2003 or BS EN 1856-2:2004.
a cast in-situ flue relining system where the material and installation procedures are suitable for use with solid fuel burning appliances and meeting the relevant requirements of BS EN 1857:2003 + A1:2008.
other systems which are suitable for use with solid fuel-burning appliances and meeting the criteria in (a).

b. liners as described in Paragraph 1.27.

*Diagram 21 Minimum separation distances from combustible material in or near a chimney *

Formation of gathers

2.21 To minimise resistance to the proper working of flues, tapered gathers should be provided in fireplaces for open fires. Ways of achieving these gathers include:

a. using prefabricated gather components built

b. corbelling of masonry as shown in Diagram 22(b); or

c. using a suitable canopy, as shown in Diagram 23; or

d. using a prefabricated appliance chamber incorporating a gather.

Diagram 22 Construction of fireplace gathers

Diagram 23 Canopy for an open solid fuel fire

Hearths

2.22 Hearths should be constructed of suitably robust materials and to appropriate dimensions such that, in normal use, they prevent combustion appliances setting fire to the building fabric and furnishings, and they limit the risk of people being accidentally burnt. A way of making provision would be to adopt the guidance in Paragraphs 2.23 to 2.28 and to provide a hearth appropriate to the temperatures the appliance can create around it. The hearth should be able to accommodate the weight of the appliance and its chimney if the chimney is not independently supported.

2.23 Appliances should stand wholly above:

a. hearths made of non-combustible board/ sheet material or tiles at least 12mm thick, if the appliance is not to stand in an appliance recess and has been tested to an applicable appliance standard to verify that it cannot cause the temperature of the upper surface of the hearth to exceed 100°C; or

b. constructional hearths in accordance with the paragraphs below.

2.24 Constructional hearths should:

a. have plan dimensions as shown in Diagram 24; and

b. be made of solid, non-combustible material, such as concrete or masonry, at least 125mm thick, including the thickness of any noncombustible floor and/or decorative surface.

2.25 Combustible material should not be placed beneath constructional hearths unless there is an air-space of at least 50mm between the underside of the hearth and the combustible material, or the combustible material is at least 250mm below the top of the hearth (see Diagram 25).

Diagram 24 Constructional hearth suitable for a solid fuel appliance (including open fires)

Diagram 25 Constructional hearth suitable for a solid fuel appliance (including open fires)

2.26 An appliance should be located on a hearth so that it is surrounded by a surface free of combustible material as shown in Diagram 26. This surface may be part of the surface of the hearth provided in accordance with Paragraph 2.23, or it may be the surface of a superimposed hearth laid wholly or partly upon a constructional hearth. The boundary of this surface should be visually apparent to provide a warning to the building occupants and to discourage combustible floor finishes such as carpet from being laid too close to the appliance. A way of achieving this would be to provide a change in level.

2.27 Dimensions shown in Diagram 26 may be reduced to manufacturer’s recommendations for appliances with surface temperatures not exceeding 85°C when in normal operation and where there is no risk of spillage of fuel or ash.

2.28 Combustible material placed on or beside a constructional hearth should not extend under a superimposed hearth by more than 25mm or to closer than 150mm measured horizontally to the appliance.

2.29 Some ways of making these provisions are shown in Diagram 27.

Fireplace recesses and prefabricated appliance chambers

2.30 Fireplaces for open fires need to be constructed such that they adequately protect the building fabric from catching fire. A way of achieving the requirements would be to build:

a. fireplace recesses from masonry or concrete as shown in Diagram 28; or

b. prefabricated factory-made appliance chambers using components that are made of insulating concrete having a density of between 1200 and 1700 kg/m³ and with the minimum thickness as shown in Table 4. Components should be supplied as sets for assembly and jointing in accordance with the manufacturer’s instructions.

Diagram 26 Non-combustible hearth surface surrounding a solid fuel appliance

Diagram 27 Ways of providing hearths

Fireplace lining components

2.31 A fireplace recess may require protection from heat if it is to provide a durable setting for certain appliances such as inset open fires. Suitable protection would be fireplace lining components as shown in Diagram 29 or lining the recess with suitable firebricks.

Walls adjacent to hearths

2.32 Walls that are not part of a fireplace recess or a prefabricated appliance chamber but are adjacent to hearths or appliances also need to protect the building from catching fire. A way of achieving the requirement is shown in Diagram 30. Thinner material could be used provided it gives the same overall level of protection as the solid non-combustible material.

2.33 Clearances shown in Diagram 30 may be reduced to manufacturer’s recommendations for appliances with surface temperatures not exceeding 85°C when in normal operation.

Diagram 28 Fireplace recesses

Table 4 Prefabricated appliance chambers: minimum thickness

Alternative approach

The requirements may also be met by adopting the relevant recommendations in the publications listed below to achieve a level of performance equivalent to that obtained by following the guidance in this Approved Document:

a. BS EN 15287-1:2007 Chimneys. Design, installation and commissioning of chimneys. Chimneys for non-room-sealed heating appliances; and

b. BS 8303:1994 Installation of domestic heating and cooking appliances burning solid mineral fuels. Parts 1 to 3.

Carbon monoxide alarms

2.34 Where a new or replacement fixed solid fuel appliance is installed in a dwelling, a carbon monoxide alarm should be provided in the room where the appliance is located.

Diagram 29 Open fireplaces: throat and fireplace components

2.35 Carbon monoxide alarms should comply with BS EN 50291:2001 and be powered by a battery designed to operate for the working life of the alarm. The alarm should incorporate a warning device to alert users when the working life of the alarm is due to pass. Mains-powered BS EN 50291 Type A carbon monoxide alarms with fixed wiring (not plug-in types) may be used as alternative applications provided they are fitted with a sensor failure warning device.

2.36 The carbon monoxide alarm should be located in the same room as the appliance:

a. on the ceiling at least 300mm from any wall or, if it is located on a wall, as high up as possible (above any doors and windows) but not within 150mm of the ceiling; and

b. between 1m and 3m horizontally from the appliance.

Note: Further guidance on the installation of carbon monoxide alarms is available in BS EN 50292:2002 and from manufacturers’ instructions. Provision of an alarm should not be regarded as a substitute for correct installation and regular servicing.

Diagram 30 Wall adjacent to hearths

Section 2: Additional provisions for appliances burning solid fuel (including solid biofuel) with a rated output up to 50kW