6.8.10 Gas – flue pipes
Flue pipes shall safely connect an appliance to a chimney, or a flue to a terminal. Issues to be taken into account include:
- size, direction and jointing
- separation from combustible materials.
6.8.10.1 Size, direction and jointing
Gas flue pipes should:
- not have adjustable draught control
- have a free area which is at least the same size as the outlet of the appliance
- not be horizontal (does not apply to balanced flues)
- if serving open-flued appliances, be vertical where possible. Where this is not possible, pipes should not be more than 45° from the vertical. The use of calculations to prove the acceptance of flue pipes installed at an angle exceeding 45º from the vertical is not acceptable
- be fixed in accordance with the manufacturer’s recommendations
- be fixed socket (as appropriate) up and be correctly aligned
- where they are long, have support directly below each socket, with a maximum spacing of 1.8m
- have appropriate access for inspection and be in accordance with relevant Building Regulations.
When connecting flue pipes to flue blocks and ridge terminals, proprietary connections should be used.
6.8.10.2 Separation from combustible materials
Single wall flue pipes should be separated from combustible materials by:
- a minimum of 25mm
- a non-combustible casing material with at least half the fire resistance of the separating wall or floor, where they pass through a compartment wall or compartment floor, or
- a non-combustible sleeve with a minimum 25mm air space around the pipe, where it passes through a wall, floor or roof.
Where double-walled flue pipes are used, the 25mm separation distance may be measured from the outside of the inner pipe.
Last updated: 2nd January 2025