Chimney and Flue Types
Class one flue
The conventional brick chimney – clearly defined by a chimney stack and pot on the roof. These are usually found in older houses, built before 1960. The flue has a 7" (180mm) diameter or greater.
Class two pre-fabricated flue
Either found in older houses with a liner in the chimney, or a newer house with a steel flue built in. The flue will have a 5" (130mm) diameter and a steel flue terminal.
Class two pre-cast flue
Found in modern houses, usually post 1960. The flue is made of pre-cast concrete flue blocks with a rectangular box section. They usually end with a ridge vent on the roof.