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Building Products March 2018

COMMERCIAL THE BEST FLUE TREATMENT Planning and specifying a commercial flue system requires knowledge of several important design criteria, as Deborah McCreadie, business development manager – commercial products, at Specflue, explains. Flues are exceptionally important structures in many buildings because they protect occupants from combustion gases that can kill, such as carbon monoxide. They also prevent excessive heat from igniting combustible materials surrounding the chimney. The operating principle of a flue is easy to understand – it simply provides a passage for conveying products of combustion to the outside atmosphere. However, its specification is not so easy to grasp. Factors that must be considered when selecting a flue for a commercial installation include efficiency, ease of installation, materials of combustion it must contain, where the proposed installation is to be situated and what ‘look’ is desired. Flue diameter is also critical – it must match the output from the appliance – and an adequate air supply is required if the appliance is to operate at its optimum. Finally, the type of flue is important. For example, a flexible liner can be installed within a brick chimney stack with clay liners, but it can’t be 62 BUILDING PRODUCTS | MARCH 2018 installed and then boxed in with timber or blockwork. A twin wall flue can rise internally or externally and will generally have a standard stainless steel finish. This can be powder coated to any BS or RAL colour so that it looks good and for protection in coastal locations. Many commercial projects such as schools, hospitals and leisure centres, now use polypropylene plastic systems as the boilers are condensing gas with very low flue gas temperatures. This could never be considered on a domestic wood stove. However, it is not just the flues themselves that must receive careful consideration; their support is also critical. Twin wall flues are supported, via support brackets, from walls, or via penetrations through floor/ceiling voids and while passing through a roof. Flexible liners hang from top support plates or hangers. A twin wall flue passing through a wall at 45º will require a large hole, which could require a support lintel to be fitted above. Flues discharge products of combustion into the atmosphere and the purpose of the Clean Air Act is to regulate how these gases can be dispersed safely. The Clean Air Act is critical to any commercial flue installation because it has an important impact on flue height. Indeed, according to the British Flue and Chimney Manufacturer’s Association (BFCMA) (www.bfcma.co.uk), chimney height is one of the main flue features used by local authorities to control the discharge of emissions into the atmosphere: “The required discharge height is calculated to render emissions harmless and not prejudicial to public health. The calculations used © Schiedel © Schiedel


Building Products March 2018
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