sean1933 Posted March 1, 2022 Share Posted March 1, 2022 Hi all. We are just in the process of building up the chimney stack which is now at eaves height. We recently attended one of the trader fairs where my wife has now firmly shifted her log burner choice to a larger model... that requires a 250mm flue rather than 150mm. Our house is designed with a large 1800 x 900 brick stack entirely outside the thermal envelope of the insulated brick and block cavity - ie externally bolted . From the outside at ground level the stack provides an opening for a BBQ. With this in mind, above the opening the stack internally splits into 2 800x800 openings to provide individual flues for the BBQ and the other for the internal log burner (which punches through the cavity into the house with a twin wall flue. The issue I have is how to build the stack. For reasons unknown the architect and SE didn't design for weight a pumice flue liners and if we fitted on only 1 side (for log burner) the stack would be notably heavier on one side. I but this issue behind me a while ago and had come to the conclusion that I either needed to use a SS flue liner (and insulate it with wrap - the stack is too large for infill vermiculate, it would be heavy and cost a fortune) or a twin wall flue fitted inside the stack - whilst a tight fit, with a 150mm flue there would still be just enough space to climb inside the stack to fit after the event and if any future checks are needed...this is out of the question with a larger 250mm twin wall especially with slight internal narrowing once it breaks through eaves level. My options now seem to be: * Build stack as it is and add a flexi flue liner - (with an insulated sleeve) after the event. This seems by far the easiest but I have on more than one occasion been told I cannot use a flue liner in a new build - but nobody appears to be able to refer me to any HETAS guidance or building regs to say why. * Before stack goes up any further, install twin wall flue now and fit the 1m sections with the stack as it goes up. This seems more robust and I know wouldn't be an issue as it is in effect outside the building envelope so functioning just like any other externally mounted twin wall flue would be, albeit it has some bricks around it too. The problem and worry I have is future access for maintenance, repair and replacement. If anyone has any guidance, especially those that can direct me to building regulation issues it would be greatly appreciated. Link to comment Share on other sites More sharing options...
sean1933 Posted March 1, 2022 Author Share Posted March 1, 2022 Link to comment Share on other sites More sharing options...
dpmiller Posted March 1, 2022 Share Posted March 1, 2022 what woodburner is it that needs a 250mm flue? Link to comment Share on other sites More sharing options...
sean1933 Posted March 1, 2022 Author Share Posted March 1, 2022 28 minutes ago, dpmiller said: what woodburner is it that needs a 250mm flue? This beast M design 1000h Link to comment Share on other sites More sharing options...
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