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Chimneys & flues
High standards – a chimney and flue update
At long last the log jam for chimney product and installation standards is starting to be cleared. Dennis Milligan, president of the British Flue & Chimney Manufacturers Association (BFCMA), looks at the latest requirements
T
he first revised standards to be published will be BSEN 1856 Chimneys, Requirements for metal chimneys System chimney products
and BSEN 15287, Chimneys. Design, installation and commissioning of chimneys. When published these standards will make Approved Document J even further out of date. The HSE is now responsible for the building standards and as yet there is no commitment to update Approved Document J. The BFCMA continues to push for the document to be updated without delay. In the meantime, the BFCMA Guides reflect the impact of the latest product standards. The guides can be freely downloaded from the BFCMA website.
Chimney/flue requirements
While the design and installation of chimneys and flues in the residential sector are covered by Approved Document J, there is no equivalent document in the commercial sector. To provide much needed guidance the BFCMA has published a Commercial Flue Guide. The guide covers chimney principles, regulations, chimney and flue design, chimney/flue height and the Clean Air Act. The aim of this guide is to provide a clearer understanding of how chimneys and flues should be selected and installed in commercial applications. The CE mark and the planned UKCA mark (UK
Conformity Assessed) are your guarantee that the product meets the prevailing product standards. After a number of false dawns, the UKCA mark is due to be implemented in 2025. The CE/UKCA mark is based on the achievement of exacting product standards, that have been developed to give the user confidence that the product is fit for purpose. Specifiers and installers should always look for the CE/UKCA mark. The CE/UKCA mark applies to both flue components and to system chimneys. The CE/ UKCA mark for a system chimney applies to the complete flue system, including add components like rain caps. The use of components that have not been tested with the flue invalidates the CE/UKCA mark and turns the flue into a custom chimney. Different types of flue will be required to
safely handle the different gases that need to be discharged. A key feature of the chimney and flue standards is a user-readable classification system that designates the features of the flue components. The features covered include temperature and pressure rating, fire, condensate, corrosion resistance and distance to combustibles. With
stainless steel components a label showing the classification must go with each flue component, so that it’s specification can be easily verified.
Chimney/flue design
The purpose of a chimney or flue is to discharge the products of combustion safely to the atmosphere. Most chimneys operate under negative pressure, relying on natural draft to transport the flue gases to the atmosphere. This requires a clear path to the top of the flue. A straight chimney/flue is always the best solution but where this is not possible, due the construction of the dwelling, the number of bends should be kept to a minimum and not exceed more than four. The angle of the bends should be no greater than 45° from the vertical, with the exception that 90° factory made steel bends or tees may be treated as being equal to two 45° bends. The chimney/flue must also maintain the
temperature of the gases above the dew point. Good chimney/flue design requires consistent insulation along the complete length of the flue. Clay, concrete and pumice liners require insulation to be prepared and added on site. Stainless steel system chimneys are supplied with effective insulation. Double wall pumice chimney systems have an air gap between the walls of the inner and outer blocks. The air gap combined with the natural insulating properties of pumice provide effective insulation. The appliance and the chimney/flue have to work together for the appliance to perform correctly. The velocity and temperature of the gases entering the flue can be important elements
in how well the chimney/flue will operate. Advances in wood burning stove technology, designed to reduce emissions have highlighted the need for sufficient draw in the chimney/flue . The BFCMA is the UK’s only Trade Association
representing the chimney and flue industry and works closely with government, public bodies and other organisations to further the interest of the chimney & flue industry. It represents the majority of manufacturers and sole distributors in the industry.
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