Understanding your Flue

A simple explanation of the various types of flues which will help you make an informed decision on which gas fire, electric fire or fireplace which is right for you and your home.

Typical Roof Brick Chimney

Class 1 Flue

A Class 1 Flue is easily recognised by a conventional brick chimney with chimney stack on the roof. This relies on the natural ´pull´ to expel the products of combustion out of the chimney pot. The minimum internal diameter for class 1 is 180mm. This allows you to have most types of fires.
Occasionally, a flue liner may have been used to rectify a leak. If this is the case the liner needs to have a minimum internal diameter of 180mm. If the liner has an internal dimension is only 127mm the chimney becomes Class 2.

 

Class 2 Pre-Fabricated Roof Flue

Class 2 Pre-Fabricated Flue

Class 2 Pre-Fabricated Flue
A Class 2 Pre-Fabricated Flue is a metal flue box that is situated behind the fire connecting to a series of metal flue pipes running up through the house terminating with a pipe and terminal through the roof. The internal diameter of the pipe is 127mm. There are a large number of fires available for this situation. Occasionally, the flue may have been constructed using 180mm pipe. If this is the case, the flue is classed as Class 1.

 

Class 2 Pre-Cast Roof Flue

Class 2 Pre-Cast Flue

Class 2 Pre-Cast Flues
Class 2 Pre-Cast Flue are commonly found in more modern homes. Constructed using hollow concrete flue blocks which create a flue up through the property usually terminating with a ridge vent on the roof. In most cases there is usually a flat wall where ther fire goes. This does limit slightly the choice of fires suitable as depth can be an issue.

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