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European Standard for chimneys
EN 15287
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British Standard for Chimneys
BS 5440 Part 1
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A flue is described as
A passage for conveying combustion products to outside air.
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A chimney is described as a
Structure surrounding a flue or flues.
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A terminal is described as
A fitting fitted to the chimney outlet.
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2nd digit of chimney code
- 1 - Natural draught
- 2 - Fan downstream of HE
- 3 - Fan upstream of HE
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Fan upstream of HE. Type of pressure.
Positive pressure
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Fan downstream of HE. Type of pressure
Negative pressure.
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Viterous enamelled steel
Internal flues only
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Components of an open flue chimney
- Primary flue
- Draught diverter
- Secondary flue
- Terminal
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Functions of draught diverter
- Protect burner from downdraught.
- Providing dilution air.
- Breaking excessive flue pull.
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Where should a terminal be located
The terminal should be located in "free air" and as far away as possible from structures or parts of the building that could create turbulence.
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How can the risk of down draught be reduced on a pitched roof.
The chimney should be routed to terminate at the highest point of the roof.
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When are terminals needed.
Terminals are needed on chimney systems up to and including 170mm diameter.
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When are chimney terminals not required.
Chimney terminals are not requires when a chimney is more than 170mm in diameter.
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General requirements for terminals
- Openings admit 6mm but not 16mm.
- Total free area of openings twice CSA
- Openings evenly distributed or on two opposite sides.
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Can balanced or fanned draught open flue terminals terminate in basement areas, light wells or retaining wells.
Balanced or fanned draught open flue terminals can terminate in basement areas, light wells or retaining wells providing that the terminal is not more than 1m below the top level of the basement, wall or light well.
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Can chimneys terminate in basement areas, light wells or retaining wells.
Chimneys can terminate in basement areas, light wells or retaining wells providing reasonable provision can be made to ensure safe disposal of the combustion products.
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Requirements of a ridge terminal.
- Not within 1.5m of an adjacent structure.
- Two or more must not be less than 300mm apart.
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Requirements of a slabbed over chimney.
Side outlets on at least 2 sides. At least 12000mm2 per chimney per side and protected by bird guards.
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Requirements of manual damper.
Should be removed or permanently fixed in open position.
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Requirements of chimney previously used with solid fuel.
Chimney must be fully swept before gas appliance is fitted.
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Requirements for flue sizes.
Not less than diameter of appliance flue outlet.
Minimum 12000mm2 for a circular flue.
Min 16500mm2 for rectangular flue - min dimension of 90mm.
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Minimum clearance between a chimney and combustible material.
25mm.
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Where a chimney passes through a slated or tiled roof, what is the minimum upstand of the purpose made plate used to weather proof the joint.
150mm
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Metalic and cement based chimney pipes must be clipped as a minimum every
1.8m
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How is condensation prevented from forming in the flue.
The chimney needs to be insulated or have minimum exposure outside of the building.
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Can chimneys be any length?
There are maximum chimney lengths for different types of appliances, above which a chimney will require lining in order to reduce the risk of condensation forming.
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Where can single wall chimneys not be used.
Single wall chimneys must not be used externally except for protrusion above the roof line.
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What is the maximum length allowed for a twin wall chimney with only an air gap between the two walls when used externally.
3m
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What must happen to a chimney if it passes through a property other than the one in which the appliance is fitted.
The chimney must be separated from the other premises by an enclosure of heat resisting material.
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What are the minimum volumes for catchment spaces
2dm3 and 12dm3
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What should a catchment space be blanked off with
A catchment space be blanked off with a closure plate and held in place with closure tape or screws and sealant.
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What is the purpose of the catchment space
The purpose of the catchment space is to provide a void where debris falling down the chimney can fall past the flue spigot and land in the bottom of the catchment space without causing any harm.
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What specification must closure tape conform to used for sealing a closure plate to a catchment space.
The closure tape should conform to specification PRS10.
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What does a brick chimney that is leaking or has a continuously burning appliance fitted to it require?
An unlined brick chimney should have a liner fitted to it.
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What are the requirements for lining a brick chimney.
The chimney must be lined with a flexible metallic liner, that is continuous and runs the full length of the chimney. The liner needs to be supported with a purpose made clamping plate
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What does unlined chimney require if it is to be connected to a gas fire and back boiler.
The chimney must be lined with a flexible stainless steel liner.
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What is secondary flue pull and when does it occur?
Secondary flue pull occurs when there is leakage through the brickwork to the point where the combustion products find it easier to flow up the outside of the liner and out through the cracks in the brickwork rather than through the heat exchanger and up the liner.
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What is the gap that is created between the liner and the chimney when a flexible liner is fitted to a back boiler installation known as?
The "Annular Space"
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What does the annular space require to have done where a flexible liner is fitted to a back boiler installation.
The annular space requires to sealed at the bottom with a plate.
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What is the purpose of the plate that is used to seal the annular space that is created when a flexible liner is fitted to a back boiler installation.
The purpose of the plate is to prevent secondary flue pull.
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What type of flue liners are not suitable for the use with gas appliances
Poured concrete flue liners are not suitable for use with gas appliances.
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Where a new masonry chimney is being lined during construction, what type of linings could be used?
- Clay flue linings conforming to BS EN 1457
- Rebated and socketed clay pipes and fittings conforming to BS 65
- Rebated or socketed flue linings made from kiln-burnt aggregate and high alumina cement
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What type of flues must not be lined
Pre-cast flues
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Why should pre-cast flues not be lined.
Pre-cast flues should never be lined as this would make them far too restrictive
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What is the minimum size allowed for new pre-cast blocks
New pre-cast flue block chimneys should have a minimum cross sectional area of at least 16,500mm2 with no dimension less than 90mm
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Where a pre-cast flue needs to change direction what must be used?
A purpose made raking or offset block must be used and must have a maximum offset of 30o
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What are pre-cast chimneys usually connected to?
Ridge terminals.
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Where a pre-cast chimney needs to travel across a loft space to connect to a terminal, what must be used?
A rigid connection between where the pre-cast flue enters the loft space and the terminal. This chimney must be at least 125mm diameter, be adequately supported (maximum 1.8m apart) and rise across the loft no more than 45o from the vertical. The chimney must be of a twin wall type.
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What is the minimum vertical rise that a pre-cast flue must have before it can change direction.
Pre-cast flues must have a minimum of 600mm vertical rise directly above the appliance connection.
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What is the maximum angle by which a pre-cast flue can travel through in order to change direction.
30 degrees
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What is a flueboost
A flueboost is a purpose made fan which can be installed into an open flue chimney to ensure the full removal of the products of combustion from the chimney if the chimney cannot otherwise meet the standards to operate safely on its own by relying on natural flue pull.
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