Fireplaces, chimneys and flues

6.8.10Gas – 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:

  1. size, direction and jointing
  2. separation from combustible materials.

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)
  • be vertical where possible (where this is not possible, pipes should not be more than 45° from vertical)
  • be fixed in accordance with the manufacturer’s recommendations
  • be fixed socket up and correctly aligned
  • where the pipes are long, have support directly below each socket, with a maximum spacing of 1.8m.

When connecting flue pipes to flue blocks and ridge terminals, purpose-made connections should be used.

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 pipes are used, the 25mm separation distance may be measured from the outside of the inner pipe.