Chimney stacks typical of a solid-fuel
flue

A Class 2 gas cowl flue

The tell-tale sign of a pre-cast flue

Class 1 Flue
Usually of masonry construction (identifiable by a chairbrick at the back of the opening), the flue must comply with the Building Regulations for Class 1 (solid fuel) appliances, with a minimum diameter of 175mm (7") and a minimum equivalent height of 3 metres.

A Class 1 flue usually terminates with a brick or stone built chimney.

Class 2 Flue
Usually of metal construction and found within newer homes.  Typically constructed using twin walled flue with a minimum diameter of 125mm (5") and a minimum equivalent height of 3 metres.

Pre-cast Flue
Usually of pre-cast concrete block construction (hollow concrete blocks which form part of the inner skin of the dwelling) that terminates with a ridge tile.

There are two main types:
a) Pre 1986 - the chimney should have a minimum cross sectional area of 210mm x 65mm throughout and a minimum equivalent height of 3 metres.

b) Post 1986 - the chimney should have a minimum cross sectional area of 16,500mm² with no dimension less that 90mm and a minimum equivalent height of 3 metres.

Power flued fire terminal vents

Standard Side Vent
A standard side vent terminal is used for both the Duo Power and the Affinity Power side vent applications.

Power 2 surface mounted Rear Vent
The Duo Power and Affinity Power can be vented directly to an outside wall, using up to 760mm of flue duct (with optional extension) to a Power 2 surface-mounted rear vent.