These pipes, which serve to prevent the formation of condensate caused by the difference in temperature between the flue gas (or combustion air) and the ambient air temperature. They consist of an external pipe of 100mm diameter and an internal pipe of 80mm, the air space between these two tubes is filled with a layer of fibre-glass which has an initial thickness of 30 mm and a density of 15 kg/m3. This insulation prevents the formation of condensation and is also fireproof. The internal pipe is supplied as male/female with an ‘O’ ring seal in the female connection. The pipes are constructed of aluminium and are only available with a painted finish; lengths are 0.5 & 1.0 metres. Since these pipes are heavier than normal, they need to be assembled using clamps.