Flue Pipe and Clearances to Combustibles

When fitting a flue system, building regulations specify clearances to combustible materials depending on the type of flue pipe. These clearances must be met to ensure legality and safety.

Single Wall Flue Pipe

Single wall flue pipe (also referred to as vitreous enamel flue pipe) must be a minimum of three times the diameter of the pipe away from a combustible material.

Twin Wall Flue Pipe

Twin wall flue pipe's clearance to combustibles is based on manufacturer guidelines and so can differ between ranges. One factor is the thickness of the insulation, which reduces the external temperature. Our range of Bofill twin wall flue has 30mm thick insulation and has a 50mm clearance to combustibles.

If the twin wall flue system is to run internally through the property and runs through spaces where accidental human contact could occur (e.g. a bedroom - not including the room where the appliance is located), the flue must be boxed in. If the flue passes through a storage space such as a cupboard or loft space, a guard must be placed no closer than 50mm around the flue pipe.

Heat Shielding

Combustible materials, such as a wall or ceiling, can be heat shielded using a fireproof board. However there must be a 12mm air gap between the heat shield and combustible material. The flue pipe must be at least 1.5 times its diameter away from the heat shield. The heat shield must extend at least 1.5 times the diameter of the flue pipe beyond each side of the flue pipe.

However always remember that fitting should only be carried out by a HETAS registered installer.