Flue Types

It is important that you have a professional fire installer check out your flue and confirm the fire suitability.  For customers purchasing a fire from ourselves we offer a free quotation service, in the Grimsby, Cleethorpes, Immingham & surrounding areas, where we will check the chimney or flue and recommend a suitable product, providing you with a written quotation for the fire and installation.  It is important that you visit the showroom prior to our making any home visit, so we can ascertain the style of fire you wish to have along with any other fireplace requirements you may need.  The following information is, therefore, provided as a guide only.

Class One Chimney:  This is usually a brick built chimney construction with either a round clay or concrete liner within or is purely built from brickwork.  This type of flue is suitable for most gas fires and solid fuel fires and stoves.

Class Two Flue:  This is generally a flexible metal liner that is fitted within a class one chimney flue.  This may have been fitted because of issues with the existing brick built chimney or if the chimney flue is very large then this may have been fitted to reduce the size of the flue to improve its function.  Another reason that there may be a liner in an existing chimney flue is if there has previously been a gas fire with a back boiler attached.

There are two types of flexible metal liners - one suitable for use with gas fires only and another suitable for use with solid fuel fires.  The liner for gas fires is a single skin construction and should never be used with solid fuel (ie: wood-burning/coal fire).  The solid fuel flexible liner is a double skinned flexible liner and this liner is suitable for use with solid fuels and gas.  The solid fuel liner is available in two grades 316/316 and 904/316 the latter of the two has a longer estimated lifespan (subject to correct use), however, the 316/316 graded liner is the most popular one used.  Flexible flue liners should only be used within an existing chimney flue, they are not suitable as a stand alone flue system.

Precast Flues:  the current regulations for the size of precast flues is 16,500mm2.  This is the size of the rectangular opening that goes up through the flue.  The current regulations state that there must be an air gap between the flue block and the finished wall and this is usually made in the form of a very shallow stud wall over the flue area and must be in the room where the appliance is fitted as well as any other rooms along the route of the flue.  Without the air gap there is a risk that the plastered finished wall could crack, damaging decorations.  Many older properties (circa 1970 to 1989) with precast flues do not have this air gap and whilst previous gas fires may have been fine when used in these flues, because of the increasing efficiencies and higher heat outputs from todays modern fires, these older flue types are just not suitable.  Older precast flues often tend to be smaller too and whilst many gas fires state ‘suitable for use with a precast flue’, this is only if the flue is built to the current regulations.  There are just a couple of fire manufacturers who have approved their fires for use in the older type of precast flue, however, professional advice must be sought before purchasing fires for use in this flue type!

Twin walled gas vent:  this is a rigid metal flue pipe system, suitable for installation internally for use with gas fires only.  With this type of flue system, generally there will be a false chimney breast in the room where the fireplace is installed and a large metal gas collection box will be fitted inside the base of the fireplace opening to which the flue system is directly connected.

Twin walled insulated chimney system:  this is a rigid metal flue pipe system that can be fitted internally or externally.  It is intended for use with solid fuel & is often used with wood-burning/multi-fuel stoves where there is no traditional class one chimney.  These flue systems can be supplied in the bare metal finish or in a powder coated black finish. 

Any new twin walled gas vent or twin walled insulated chimney system should be fitted by a suitably qualified installer and a certification for the work obtained.  We are both Gas Safe and HETAS registered and can supply and fit your new chimney system, providing certification and registration to the appropriate governing body.  Please note, we do not certify work carried out by others.

Balanced Flue:  this is a flue system that comes as an integral part of a specific balanced flued gas fire.  Normally, these fires are fitted when there is no other flue option available and are for use with gas only.  There is a good range of options for balanced flue gas fires now including fireplace/hearth mounted models and hole in the wall style.  Balanced flue fires are always glass fronted.  This is because of the way that a balanced flue fire works, with a double tube that goes through the wall to the outside, allowing cold air to be drawn in to feed the fire via the outer part of the tube and the products of combustion being forced out through the inner part of the tube, a function which would not work if the glass front of the fire were not there.  These fires offer some of the highest efficiencies available because of the flue system.  Some models can be fitted to a standard cavity wall without the need to build out a false wall, however, there are some much bigger fires available that will require a false chimney breast being built in order to achieve the look you desire.

Powered Flue:  this type of flue uses electric to draw the products of combustion away via the use of the mechanically powered flue system.  Fitted in a similar way to the balanced flue fires, the flue is taken through the wall with a terminal box on the outside wall.  These fires are now being rapidly replaced by more efficient balanced flued versions which do not require electricity to operate.  Power flue fires are open fronted, are described as decorative only appliances and do require both gas and electric to work.

No Flue At All:  if you do not have any type of flue in your property and no outside wall for a balanced flue fire to be fitted to, then the only other option that we offer is an electric fire.  There is a huge range of electric fire options available now and whilst electric fires are not designed to provide high heat outputs, they are perfect for creating a cosy looking feature fireplace in your home.  Electric fires are for use in well insulated spaces and occasional use and are not a primary source of heat.  We have electric fires in traditional and contemporary styles: see our ‘Electric Fires’ page for some more details.


Burning Sensation Grimsby Ltd

Grimsby’s Premier Fireplace Showroom

Armstrong Street, West Marsh Industrial Estate, Grimsby, N E Lincolnshire.  DN31 1XD

Tel: 01472 351651   Email: sales@burningsensation.co.uk