A London gather hood is commonly installed when fitting flexible flue liner above an open fireplace. It creates a larger area for the flow of gasses to escape and pass up the chimney liner to terminate. The gather hood comes with an adaptor to attach the flexible flue liner to - the gather hood is attached to the base of the chimney and at the top of the chimney chamber, the metal flaps are folded at right angles and screwed into the brickwork.