INTERIORS


Reducing flue risk


It’s easy to overlook the importance of chimney and flue design, says Dennis Milligan of the British Flue and Chimney Manufacturers Association, explaining some of the basic rules to bear in mind


W


hen constructing a new dwelling, the route of the chimney needs to be thought about – at the design stage. Most residential chimneys/flues rely on natural draught – the pressure difference between cold and hot air – to draw the flue gases up the chimney to the atmosphere. A potential reduction in velocity and temperature could reduce the draw of the chimney or flue. A straight chimney is always the best


sep/oct 2021


solution, but where this is not possible, due to 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. One of the keys to a well performing chimney or flue is consistent insulation along the complete length of the flue. The last thing you want is for the temperature of the gases to fall below the dew point. Clay, concrete and pumice


liners require insulation to be prepared and added on site. Stainless steel and clay 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 provides effective insulation along the length of the chimney. Maintaining the flue gas temperature will enable the flue gases to freely escape to the atmosphere.


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