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Building regulations need to be understood and carefully followed when installing a new stove, chimney or flue. Building regulations provide for a safe installation and cover key areas such as chimney & flue safety, the hearth, clearances to combustible materials and ventilation. To view the current building regulations applying to stove, fireplace and flue installations in full, click HERE or alternatively you can contact the building control department of your local council for up-to-date information. To view information about the Competent Persons Scheme click here – https://www.competentperson.co.uk/pdfs/buildingworkleaflet.pdf
It is important to point out that although all work effecting stoves, chimneys and flues is governed by building control, work carried out by a HETAS registered installer can be self certified to confirm it conforms. Work carried out by an unregistered engineer must be inspected by your local building control officer. On completion a Data Plate will be fitted to confirm building regulation compliance.
Chimney Condition & Suitability
Before installing a new stove the chimney should be inspected to ensure it is structurally sound, clear of obstructions and the correct diameter for the appliance to be used.
A smoke test should then be carried out to check for gas tightness at which point it is recommended that the chimney is swept. A chimney found to be leaking must be relined.
Re-lining an existing chimney
A way of relining a chimney would be to use an independently certified flexible metal flue liner, specifically made to suit the types of fuels to be burnt. Remember that a solid fuel stove will use a different liner to a gas stove. Flexible metal flue liners should be installed in one complete length without joints within the chimney.
Other suitable materials are listed in the current HETAS guide. If a chimney has been relined in the past using a metal lining system and the appliance is being replaced, the metal liner should also be replaced.
Flue Size
The diameter of any flue used (stove flue pipe, liner or twin wall pipe) must not be smaller than the size recommended by the stove manufacturer – generally the diameter of the stove outlet.
If a wood burning stove has a diameter of 125mm (5″) then Building Regulations do recommend using a larger 150mm (6″) liner, however manufacturers installation instructions do take priority.
Flue Height
Flues should be high enough to ensure sufficient draught to clear the products of combustion. A flue height of 4.5m should create a sufficient draw providing although this can be affected by the height of the building, number of bends and winds patterns. Flue height is subject to a number of other calculations.
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. The diagram below shows flue outlet positions which meet the requirements in common circumstances.
Flue Height Picture
Point where flue passes through weather surface Clearances to flue outlet
A At or within 600mm of the ridge At least 600mm above the ridge
B Elsewhere on a roof (whether pitched or flat)
At least 2300mm horizontally from the nearest point on the weather surface and:
a) at least 1000mm above the highest point of intersection of the chimney and the weather surface; or
b) at least as high as the ridge
C Below (on a pitched roof) or within 2300mm horizontally to an openable rooflight, dormer window or other opening At least 1000mm above the top of the opening
D Within 2300mm of an adjoining or adjacent building, whether or not beyond the boundary At least 600mm above the adjacent building
Notes
1) The weather surface is the buildings external surface, such as its roof, tiles or external walls.
2) A flat roof has a pitch less than 10°
3) The clearances given for A or B, as appropriate, will also apply.
If the roof covering could be easily ignited it is recommended the flue height is increased. A simple rule of thumb would be 1800mm above where it penetrates taking into account earlier requirements.
Flue to combustible material distances
Single skin, un-insulated flue pipe must be at least 3 times it’s diameter from combustible materials e.g. A 150mm (6″) pipe needs to be a minimum of 450mm (18″) from combustible material.
It is possible to use a heat shield to reduce this distance to 1.5 times it’s diameter, providing the heat shield extends at least 1.5 times the flue’s diameter to each side of the flue and there is an air gap of at least 12mm between the shielding material and the combustible material.
Double skin, insulated flue pipe can reduce the clearance required to combustible materials to 50mm.
Twin Wall Flue Pipe (Factory Made Metal Chimney)
Where a factory-made metal chimney passes through a wall, a sleeve should be provided to prevent damage to the flue or building through thermal expansion.
To facilitate the checking of gas-tightness, joints between chimney sections should not be concealed within ceiling joist spaces or within the thicknesses of walls.
When providing a factory-made metal chimney, provision should be made to withdraw the appliance without the need to dismantle the chimney.
Hearth Requirements
A hearth is constructed of non-combustible material and is used to protect nearby combustible material from the heat of the stove and from hot fuel that could potentially fall from the stove.
A stove must stand on a non-combustible plinth extending a minimum of 300mm in front & 150mm out from the stove at the sides. The edges of the hearth should be clearly marked e.g. a change in level.
Hearth Thickness: Models that have been designed and tested to have a hearth temperature not exceeding 100° centigrade, may use a 12mm hearth. Untested stoves must either use a 125mm thick hearth with a 50mm air gap underneath or a solid 250mm thick hearth. The later two measurements can include a Constructional Hearth which is unseen and built below floor level, finished with a Superimposed Hearth which is the finished material on which a stove will sit.
Ventilation for stoves
As stoves take air from the room in which they sit to aid combustion, it is likely that you will need to install a permanently open air vent into the room. The size and requirement of the vent will depend on the air permeability of the room:
If the design air permeability is greater than 5.0 m3/h.m² the requirement is 550 mm² per kW of rated output above 5kW. e.g. for 8 kW this would be:- (8-5) x 550 = 3 x 550 = 1,650 mm2/16.5cm².
If the design air permeability is less than 5.0 m3/h.m2 the requirement is 550 mm² per kW of rated output above 5kW. e.g. for 8 kW this would be:- 8 x 550 =3 x 550 = 4,400 mm2/44cm².
Note: It is unlikely that a dwelling constructed before 2008 will have an air permeability of less than 5.0 m3/h.m² at 50Pa unless extensive measures have been taken to improve air tightness.
These requirements do alter in the unlikely event that the appliance is fitted with a flue draught stabilizer (refer the Document J of building regulations for further information).
A vent can be placed in the walls or the floor of the room containing the stove and can either vent directly outside or through another room or loft space which has permanent ventilation to outside.
Notice Plates or Data Plates
Where a hearth, fireplace, flue or chimney is constructed or altered a permanent notice plate should be fixed at an appropriate position such as next to the chimney, electric meter of stop-cock, giving details of the location of the fireplace, the type and size of the flue and type of heating appliance used.
Carbon Monoxide Detectors
It is now mandatory to fit a Carbon Monoxide alarm within the room whenever a new or replacement solid fuel appliance is installed in a dwelling. This alarm must be a permanently installed type, rather than a portable type, and should incorporate self-test and audible alert if the battery or detector cell develop a fault. Siting of the alarm must meet the following criteria:
a) on the ceiling at least 300mm from any wall or, if it is locatioed on a wall, as high up as possible (above any doors and windos) but not within 150mm of the ceiling; and
b) between 1m and 3m horizontally from the appliance.
All new or replacement fixed solid fuel or wood/biomass appliances installed in a dwelling a carbon monoxide alarm must be fitted in the same room as the appliance.