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No chimney no problem! What is a Twin Wall System

Posted on 16 June 2017

Twin wall flue pipe is a type of flue system used when a traditional chimney stack is not available. Twin wall flue is used to get rid of exhaust gases from a wide range of appliances including wood burning or multi-fuel stoves, pellet stoves, boilers, incinerators, ovens and air conditioning systems.

The Twin Wall flue is essentially a flue pipe, inside another flue pipe with a layer of insulation between the two pieces. This layer ensures that the exterior of the twin wall flue does not get hot enough to cause damage to surrounding structures, (although it does get warm to the touch).

Twin Wall systems are available with a full range of fittings so you can build an entire chimney. The pieces are designed to push fit together and then sealed with a locking band. In some systems, the wall brackets also double up as locking bands-thus doing two jobs at once. A Twin Wall system can be used to construct a chimney in a house where there is no traditional chimney stack, or to position a Wood Burner in a room with no chimney (StoveMaestro.co.uk 2017).

The installation of these systems in governed by the UK Building Regulations, primarily to ensure the safety of the occupants and neighbours of a property with such a flue. These are concerned with preventing a fire and preventing the leakage of potentially toxic chimney gases (such as Carbon Monoxide) into the building. This type of installation provides a solution for many modern houses where no chimney was installed,  because it was thought gas or electric central heating systems were going to be the only methods of heating homes for the next 100 years (StoveMaestro.co.uk 2017)

Twin Wall flue is also known as DW (Double Wall) or HT (High Temperature) flue. Twin wall flue pipe cannot be cut to length by you to make it fit. So the process needs to be planned carefully when installing a twin wall flue chimney.

The Twin Wall flue pipe is a 'clip-together' or 'push fit' chimney system that can be used to safely take the combustion gases from a wood burning stove up to the atmosphere.

Twin wall flue is a metal tube (flue) insulated with approx. an inch of insulation (two layers of stainless steel with insulation between). The insulation is necessary to keep the gases hot. Were you to use non-insulated flue pipe for the whole of your chimney, then the gases would likely cool too much and start to slow rather than rise with this causing the smoke underneath to "dam". This might cause the smoke below to exit out of the vents in your stove instead of the top of your chimney. Cooling gases also form condensation which forms on the inner walls of the flue and runs down into the stove (mixed with soot it is a disgusting brown liquid) (stovefittersmanual.co.uk 2017).

You must notify Building Control prior to installing any chimney (unless you are approved to self certify, as are HETAS engineers). Steel vitreous stove pipe (non-insulated),  MUST NOT be used to go through a wall or ceiling, except directly into a chimney. If you need to exit the room, whether out through a wall or through a ceiling then you must use Twin Wall flue pipe to the cowl (unless going into a chimney higher up).

The flue will most likely have an inner diameter of 5" or 6" but, this depends on the diameter of the flue that the stove requires. A 5" can be used if the stove is DEFRA approved and the manufacturer does not state 6" as a minimum.

Twin Wall flue is generally available in silver (reflective chrome-like) and black (satin/matt finish). The black is a little more expensive. Quality Twin Wall flue is expensive but, cheap when compared to building a new chimney. Twin Wall flue can travel internally within a building, or externally on an outside wall.

Overall, Twin Walls can provide a solution to lots of heating problems around the home, and help you save money on gas and electric bills. StovesWorld UK do not recommend, or even advise that this system can be installed by yourselves if you do not have the important qualifications and training to do so. It is always advised that you have a qualified HETAS installer to do the work. Cutting corners can cost LIVES, and if you are not using a registered HETAS installer to do the work, make sure that you are always complying with the UK Building Regulations (including getting the completed installation checked and certified as safe). Home insurance will be VOID if this is not done correctly.

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