A chimney, simply put, is a vertical tube designed to draw combustion products (smoke and gases) from an appliance like a wood burning stove or fireplace to the atmosphere outside the house. If your house was built before the 1960’s it will have originally been built with chimney breasts in the lounge and dining room which pass through the bedrooms directly above, the loft space and then out through the roof. These were to accommodate fireplaces that were used to heat the rooms at a time before central heating was available.
Chimneys are categorised into ‘classes’.
A Class 1 chimney is common in houses built up until the 1960s. They consist of a brick-built stack situated on either an internal or external wall and containing multiple flues for multiple fires (although the fires cannot share a flue). This type of chimney can be used with all types of solid fuel fires wood burning and multi fuel stoves and gas fires too.
Class 2 (5” diameter) gas flue systems are often found in houses built from the 1960s onwards. They consist of an interlocking metal pipe running through the house, but can be used with certain types of gas fire only. Class 2 (pre-cast) systems consist of a rectangular hollow cavity made from concrete or clay blocks, travelling up the wall cavity to a ridge vent or metal flue terminal on the roof. They can be used with slimline gas fires.