Copyright Gasflair 2012   1.1  

The Home Heating and Cooking Specialists

Installation & Surveys     Price Promise    Special Offers      Product Guides     Showrooms     Contact Us

Terms and conditions

Product Guide: Flues

Product guides are for general advice only.  Every installation situation is different.  For more specific advice from one of our experts please visit you local Gasflair showroom.

<<Back to Product Guides Menu

Class 1 Flue
This is usually a brick chimney of a minimum internal diameter of 7 inches. This type of flue will usually accommodate any type of open flued gas fire. Be wary of chimneys that have previously has a gas back boiler and fire installed as they may have a 5 inch diameter flexible flue liner installed inside them (in effect making them a Class 2 flue).

Class 2 Flue
These flues are usually Class 1 flues (chimney) lined with a flexible flue liner of 5 inches diameter or 'twin wall' rigid metal flue pipes. A metal tube or terminal emerging from the roof can indicate the presence of a Class 2 flue.

Pre-Cast Flue
House builders began to install this type of flue in new houses in the 1970's in order to save the space that a chimney breast would occupy in the room. They are constructed from pre-cast concrete blocks that are built into the structure of the house. Due to the narrower depth and smaller cross-sectional area of the flue not all fires can be installed in this type of flue. Some pre-cast flues, usually in newer houses have a small 'chimney breast' that protrudes into the room 4 or 5 inches; others have no protrusion at all.

Balanced Flues and Fanned Flues
Balanced Flues go horizontally through the outside wall of the house. A balanced flue exits from the back of the gas fire and obtains its air for burning from the outside. It in turn expels the products of combustion (gas fumes) to the outside through the same flue. The balanced flue is manufactured as part of the gas fire and cannot be installed separately.

Fanned flues look similar in appearance to balanced flues but take their air for burning from the room in which they are installed. They use an electrically powered fan to expel the products of combustion horizontally to the outside. Some older type fanned flue fires were fitted on internal walls with flue pipes that run several metres to an outside wall and even around corners, although most manufacturers have discontinued these models now.

Please remember that installing gas appliances is not a DIY job. All gas appliances must be installed by a qualified Gas Safe registered engineer (Gas Safe have replaced CORGI).  The information given here is a guide only. To confirm suitability of any gas fire to work correctly with your flue or chimney you should employ a qualified Gas Safe registered engineer to conduct a site survey and report. We recommend that you have your flue checked prior to ordering, as the return of an unsuitable product that is not faulty may incur a handling and re-stocking charge.

Gasflair provide local installation services and surveys- contact your nearest showroom for further information.