General
The guidance in this Section should be read in conjunction with guidance given in Section 1.
Requirements for the installation of gas burning appliances (natural gas and liquefied petroleum gas (LPG)) are contained in I.S. 813:2014 Domestic Gas Installations and I.S. 820:2010 Non-domestic Gas Installations. Additional guidance for specific appliances is contained in the following standards and codes of practice:
I.S. EN 449:2002 (LPG Appliances – Domestic flueless space heaters);
I.S. EN 509:2000 (Decorative fuel-effect gas appliances);
BS 5546:2010 (gas appliances providing hot water supplies for domestic purposes);
BS 5864:2010 (ducted-air heaters);
BS 6173:2009 (catering appliances).
All gas appliances should be installed and commissioned by a competent person and in accordance with the requirements of the Commission for Energy Regulation (CER).
Fixed flued gas fires
There are three main types of such fires (see Diagram 15):
(a) radiant convector gas fires,
(b) inset live fuel-effect (ILFE) fires, and
(c) decorative fuel-effect (DFE) fires - may be inset in a fireplace or fitted under a canopy.
Installation of appliances should be in accordance with the relevant recommendations of I.S. 813:2014. Decorative Fuel and Inset Live-Effect fires exceeding 15 kW input should not be installed in domestic dwellings.
Diagram HJ15 - Examples of fires - Extract from TGD J
Fixed flueless gas fires
This type of appliance discharges the products of combustion to the room in which it is situated. This type of appliance should not be installed for use as a primary source of room heating. Installation should be in accordance with the relevant requirements of I.S. 813:2014.
Appliances in bathrooms and garages
Any appliance in a bath or shower room or a private garage must be of the room-sealed type.
Air supply to appliances
*Flueless appliances
When locating any flueless appliance reference should be made to Table 3 and I.S.813:2014 for locations permitted and air supply required as combustion products from these appliances are released directly into the
room where they are located.
Table HJ3 - Locations and permanent ventilation requirements for flueless appliances - Extract from TGD J
Open-flued appliances
Any room or space containing an open-flued appliance should comply with the requirements as set out in Table 4 for permanent ventilation openings.
Additional guidance regarding the size and positioning of ventilation openings, including guidance for when there is more than one open-flued or flueless appliance in a room or space and for when the appliance is situated in a compartment is contained in I.S. 813:2014 and I.S. 820:2010.
Table HJ4 - Air supply - Open-flued heating appliances - minimum ventilation opening requirements - Extract from TGD J
Flues
Open-flued appliances
Flue size
The flue size should be at least the following:
(a) Flues for Decorative Fuel-Effect (DFE) fires should have a minimum dimension, (circular or square), not less than 175 mm, or a cross sectional area of 32,000 mm2 if the flue is rectangular, and have a minimum dimension of 90 mm,
(b) Flues for Inset Live Fuel Effect (ILFE) fires should have a minimum dimension, (circular or rectangular), not less than 125 mm,
(c) Flues for other open-flued gas fires should have a cross-section area of at least 12,000 mm2 if the flue is round, or 16,500 mm2 if the flue is rectangular, and have a minimum dimension of 90 mm, and
(d) Flues for any other appliance, should have a cross-sectional area of at least that of the outlet from the appliance.
The cross sectional area of the flue at the appliance should be maintained or increased along its length in accordance with the manufacturer’s recommendations. The cross sectional area should not be reduced at any point along the length of the flue.
Flue direction
For natural draught flue: 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 700 mm. If a bend is necessary in a flue, it should not make an angle of more than 45° with the vertical. Where the use of angles greater than 45° from the vertical cannot be avoided, the following should apply:
no downward sloping sections should be permitted;
angled sections should not exceed 700 mm in total length;
the minimum vertical height of the flue should be 1.3 m.
For non-natural draught flue: reference should be made to the appliance or flue manufacturer’s instructions.
Concealed flues
Where a metal or plastic chimney system is routed within a void and consists of more than 2 joints, appropriate means of access at strategic locations should be provided to allow a visual inspection to ensure the following:
the flue is continuous throughout its length,
all joints appear correctly assembled and appropriately sealed,
the flue is adequately supported along its length,
any required gradient of fallback to the boiler is provided.
Outlets from flues
The outlet from a balanced-flued appliance should be:
so situated externally as to allow free intake of air and dispersal of products of combustion, and
protected with a guard if persons could come into contact with the terminal or if it could be subject to damage, and
designed so as to prevent the entry of any matter which might restrict the flue.
The outlet from any other appliance should be:
so situated at roof level, that air may pass freely across it at all times, and
fitted with a flue terminal if the flue outlet is less than 175 mm measured across the axis of the flue and the appliance is not a gas fire or
fitted with a guard to prevent the entry of any matter which might restrict the flue where the outlet is greater than 175 mm.
Table 5 gives appropriate distances for terminals as shown in Diagram 16.
Diagram HJ16 - Location of flue outlets for gas appliances - Extract from TGD J
Table HJ5 - Flue terminal locations (see Diagram 16) - Extract from TGD J
Note: The flue terminal positions are in accordance with the safety distances set out in I.S. 813. Consideration may be given to siting a condensing boiler flue terminal such that the plume of wet flue products does not impinge on or significantly affect the use of the dwelling and also the neighbouring buildings. Care may need to be taken to locate flue outlets from condensing boilers away from parts of a building that may be damaged by frequent wetting. The direction of the flue may be altered by specialist diversion kits which should be appropriate for the flue, appliance and fuel being used. Further detailed guidance regarding the location of flue outlets is contained in I.S. 813:2014 and I.S. 820:2010.
Diagram HJ17 - Open-flued gas terminals exiting through or adjacent to roof - Extract from TGD J
Diagram HJ17b - Gas flue terminal adjacent to a window or roof light on pitched roof - Extract from TGD J
Chimneys and connecting flue pipes
The minimum I.S. EN 1443:2003 designations (see sub-section 1.4.4) for chimneys and connecting flue pipes are shown in Table 6.
Table HJ6 - Chimneys and connecting flue pipes - Extract from TGD J
Connecting flue pipes
Materials
Connecting flue pipes may be of any of the following materials:
(a) any material described in Section 2 for a solid fuel appliance, or
(b) sheet metal flue pipes as described in I.S. EN 1856-2:2009.
Flue pipes with spigot and socket joints should be fitted with the sockets uppermost.
Shielding
Flue pipes should:
(a) be at least 25 mm from any combustible material, or
(b) where passing through a wall, floor or roof, be separated from any combustible material by a non-combustible sleeve enclosing an air space of at least 25 mm around the flue pipe, or
(c) where passing through a compartment wall or a compartment floor, be cased with noncombustible material with at least half the fire resistance needed for the wall or floor (see Technical Guidance Document B - Fire Safety).
For a double-walled flue pipe, the 25 mm distance may be measured from the outside of the inner pipe.
Chimneys
Masonry chimneys
Masonry chimneys should be lined with any material described in Section 2 for a solid fuel appliance. For condensing appliances, clay/ceramic flue liners with rebated or socketed joints meeting Class B2N1 or B2N2
as described in I.S. EN 1457- 2:2012 may also be used. Specific care should be taken where the liners have a water vapour diffusion class of WB, WC or WD (see manufacturer’s instructions).
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 brickwork should be filled with weak 1:1:12 cement/lime/sand mortar or insulating mix as specified in sub-section 2.5.3.
Flue block chimneys
Flue block chimneys should be constructed of factory made components suitable for their intended use. They may incorporate a flue or be lined. Flue blocks suitable for use with gas-fired appliances include:
(a) any flue block described in Section 2 as suitable for solid-fuel appliances;
(b) flue blocks meeting the performance level specified in sub-section 3.7.1 for gas-fired appliances. These include:
(i) clay/ceramic flue blocks as described in I.S. EN 1806:2006. The appropriate Classes for use with natural draught appliances, fanned draught appliances and condensing boilers are Class FB4 N1, FB4 P1 and FB5 P1 respectively, unless otherwise specified by the manufacturer (see Table A5),
(ii) concrete flue blocks as described in I.S. EN 1858:2008. The appropriate Classes for use with natural draught appliances, fanned draught appliances and condensing boilers are Class E1, E3 and G1 respectively, unless otherwise specified by the manufacturer (see Table A6).
Wall thickness
The wall thickness of a brick or blockwork chimney or flue block chimney should be at least 25 mm. Any chimney wall which:
(a) is part of the wall of a compartment of the same building, another building or another dwelling, should give at least the fire resistance needed for the compartment or separating wall (see Technical Guidance Document B - Fire Safety), or
(b) passes through a compartment wall or a compartment floor, should have at least half the fire resistance needed for the compartment wall or floor (see Technical Guidance Document B - Fire Safety). If the compartment wall or floor is masonry material, it may also form the chimney wall.
Metal system chimneys
Metal system chimneys should be double-walled insulated chimneys as described in Sections 2 for solid-fuel appliances. Alternatively metal system chimneys complying with I.S. EN 1856-1:2009 or system chimneys
with plastic flue liners complying with I.S. EN 14471:2005 and meeting the performance level specified in sub-section 3.7.1 and Table 6 may be used.
The heating appliance should not support the weight of the chimney except when the heating appliance manufacturer states in his instructions 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. The spacing of supports and unsupported height declared by the manufacturer should not be exceeded.
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. Chimneys in accordance with EN 1858 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 IS EN 1856- 2:2009 and meeting the performance level specified in sub-section 3.7.1 and Table 6 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 gas 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 left empty unless this is contrary to the manufacturer’s instructions.
Flexible flue liners may not be appropriate for large non-lined chimneys without specialist advice.
*Debris collection space
Where the chimney is not lined or not constructed of flue blocks as provided for in the guidance in this document, then a debris collection space should be provided at the bottom of the chimney with a volume of
at least 0.012 m3 and a depth of at least 250 mm below the point of connection of the appliance with the chimney. The space should be readily accessible for clearance of debris, for example by removal of the appliance.
Hearths
A hearth should always be provided for an appliance unless:
(a) every part of any flame or incandescent material in the appliance will be at least 225 mm above the floor, or
(b) the product standard provides for a hearth not being necessary and the appliance complies with the appropriate parts of the standard. The following is a list of some such standards.
I.S. EN 26:1998 - Instantaneous water heaters
I.S. EN 30 (all parts) - Cookers
I.S. EN 89: 2000 - DHW heaters
I.S. EN 297:1994 - Central heating boilers
I.S. EN 449:2002 - LPG Flueless appliances
I.S. EN 483:2000 - Type C boiler
I.S. EN 778:2009 - Forced convection airheater
I.S. EN 1266:2002 - Convector heaters
I.S. EN 1319:2009 - Air heaters
BS 7977-1:2009 - Radiant convector
In the case of a back boiler, the hearth should be constructed:
(a) of solid, non-combustible material at least:
(i) 125 mm thick, or
(ii) 25 mm thick placed on noncombustible supports at least 25 mm high, and
(b) to the size given in Diagram 18.
In the case of any other appliances, the thickness of the solid non-combustible material may be reduced to 12 mm. The hearth size should be as shown in Diagram 18.
Diagram HJ18 - Hearth sizes - Extract from TGD J
For ILFE and DFE gas fires the hearth thickness may be reduced as above and extend at least 300 mm forward from the face of the builders opening or outer edge of the incandescent fire bed and at least 150 mm beyond
each edge of the naked flame or incandescent radiant source (see Diagram 15).
Shielding of appliances
Unless the appliance complies with the appropriate parts of the standards listed in subsection 3.10.1(b), which provide that a shielding of the appliance is not necessary, the backs, tops and sides of appliances and any draught-diverters should be separated from any combustible material by either:
(a) a shield of non-combustible material at least 25 mm thick, or
(b) an air space of at least 75 mm (see Diagram 19)
Diagram HJ19 - Separating appliance from combustible material - Extract from TGD J
