Burning Sensation (Grimsby) Ltd



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Flue Types


What Flue Type?

If you are unsure as to the type of flue you have you must get this checked prior to purchasing your new appliance by a suitably qualified GAS SAFE/HETAS REGISTERED installer. If you do not have a fitter, we offer an in-house Gas Safe/HETAS fitting service where required. Prior to purchase we will carry out a site survey, so that we can provide you with a full detailed written quotation for the supply & installation of the appliance/fireplace you have chosen. For areas outside of Grimsby a small fee will apply. If you are unsure as to which appliance to choose, once we have visited your property we can advise the most suitable. For more details on our fitting service see our ‘Fitting Service’ page.

Brick Chimney: this is usually a visible brick/stone built conventional chimney breast (in two storey buildings it will be in the room above – although may be slightly narrower in width upstairs) and there will be a stack on the roof with pot. Solid fuel can be burned in this type of flue. There is a vast selection of gas fires available for this type of flue. Open pots may require a gas cowl to stop birds & debris falling down the flue & to help against rain coming down the flue.

Metal TWI Chimney System: This type of system is ideal for homes who want to have a solid fuel appliance but do not have an existing traditional chimney. This type of chimney system can be fitted internally or externally. The metal liner is twin walled & insulated, ensuring the outer part of the chimney stays cooler & also to alleviate flue chill (flue chill is usually caused by the use of single skin flue liners, which stops the flue from working correctly). Normally twin wall insulated flue systems are in a steel finish but they can be supplied in a powder coated black finish, if required. The overall external dimensions for a five inch liner would be approximately seven inches, a six inch liner would be approximately eight inches externally and so on. When fitting a full TWI externally on a building, we recommend you contact your local planning department prior to having the system fitted.

Pre-fabricated/Class 2 flue: this type of flue is generally a single skin metal flue liner with a gas collection box (big metal box connected to the liner) in the fire opening, it is also used to line an existing brick chimney where the existing brick chimney is faulty. Usually there will be a chimney breast visible either in the room or on the outside wall to allow for the depth of the gas collection box & to provide insulation for the flue system. This type of flue should not be confused with a pre-cast flue, which has a very similar if not the same type of round metal terminal cowl. There are different types of flexible metal liners available for lining an existing chimney - one to suit solid fuel & one to suit gas fires & there are different grades of metal quality available.

Pre-cast flues: this type of flue is usually built into the wall, so the wall will be flat or sometimes a very shallow breast will protrude into the room. The flue is built in blocks that go up the inside of the wall to the loft, where a header block will be found followed by a metal gas flue pipe of usually 5” diameter. The metal pipe travels out onto the roof & has a metal pipe with GC1 gas cowl.

No chimney:this means that the wall where you want to put the gas fire does not have any kind of flue. As long as the wall is an outside wall you can choose from a variety of balanced flued (glass fronted) or power flued (open) living flame gas fires. If you are replacing an existing balanced or power flued gas fire – you will need to replace the complete fire & flue system, you cannot use the old flue system with a new fire. With new builds often not incorporating flues these days, the number of balance and power flue fires has increased so that there is a good selection available – even contemporary hole in the wall style!

Note regarding solid fuel stoves: as stoves are increasing in popularity, we are often asked if an existing masonary chimney requires a metal liner. The simple answer is - if the chimney is in good working order, a metal liner is not required as the clay liner is the flue liner! The only time you would need to fit an additional metal flue liner into an existing masonary chimney, is if the existing chimney is faulty, very large, if it is very old or hasn’t been used for a long time or if manufacturers instructions require the installation of a liner with their particular appliance. It is not necessary to line a perfectly good, traditional masonary chimney. Stoves are connected to an existing masonary chimney by the installation of a register plate with gasket seal, this makes the seal between the chimney & the vitreous enamel flue pipe that comes off the stove.