Schiedel B Vent Flue Vent Pipe - 150mm x 450mm Part of the twin wall gas venting system for residential and small commercial gas appliances with input up to 60 kW. Suitable for internal and external use, either as a complete system or in combination with flue blocks or brick chimneys. Must not be used for oil-fired or solid fuel systems. Note that for external runs exceeding 3 metres, BS 5440-1:2000 requires the use of a stainless steel insulated flue. The ICID Flue range meets this requirement.