Class 1 flue
7 inches or more in diameter.
Usually found in brick properties built before 1960.
Most gas fires will fit a Class 1 flue.
Class 2 flue
A circular flue or flue liner only 5 inches in diameter.
Most gas fires can be fitted in a class 2 flue
Usually found in newer properties.
The pre-cast flue is made from blocks that fit in the cavity of an outside wall.
There are less fires made for this type of flue.
Usually fitted to an outside wall when no chimney is available.
The fire takes air from the room and a fan fitted outside removes the gases
A Balanced flue
Usually used where there is no chimney.
This type of flue takes air in from outside, through the fire by convection and then expels the burned gases.