13. Installation – fluing off the top (b) into an existing masonry chimney.

'Top fluing' promotes the best possible chimney performance and is a popular way to connect cookers and some stoves into an existing chimney. In this instance it is necessary to incorporate a bend. If the bend is raised 600mm on a vertical section (A), draught performance is helped since flue gases within that section are at their hottest and most buoyant and will exert a useful upward thrust.
XXThe bend should allow the flue to enter the chimney at an angle not less than 45° so that a strong upward draught is maintained. And a removable soot door (B) is essential to permit a cleaning brush to be pushed both upwards into the chimney and downwords into the stove.
XXFinally, make sure you can get the soot out when you sweep the chimney! The way to do this is to provide a trap served by a soot-door located inside or outside – whichever is the more convenient. The soot-door must be 'double seal' when it serves a closed stove, to ensure it is airtight. 'Single seal' soot doors are suitable only for use with an open appliance.