About Gas Fires & Flues

IMPORTANT:Gas fires are not suitable for DIY fitting and must be installed by a Bord Gais registered fitter.

Class 1 Flue

Usually a standard brick chimney of a minimum internal diameter of 7 inches. This type of flue will usually accommodate any type of open flued gas fire.
Note: Chimneys that have previously had a gas back boiler and fire installed may have a 5 inch diameter flexible flue liner installed in them. These are not suitable for a Class 1 gas fire but require a Class II.

Class 2 Flues

These flues are often Class 1 chimneys 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 II flue. A number of new homes are now being fitted with Class II flues as standard.

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 Powered 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 by means of a twin walled flue. 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.

Powered 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 powered flue fires (such as our Side Vent Gas Fire) can be fitted on internal walls with flue pipes that run several metres to an outside wall and even around corners.