A heat exchange unit (100) for hot gas recovery comprising, an inlet duct (34) to which a heat exchange duct (59) and a bypass duct (58) are connected, one being surrounded by the other, a heat exchange array (2) situated within the heat exchange duct (59) and a damper (50) arranged to direct the flow of gas through the unit (100), such that the damper (50) is situated within the inlet duct (34) and has two extreme positions, such that in a first extreme position the damper provides a first continuous surface and substantially seals one of the heat exchange and bypass ducts from the inlet duct and in the other extreme position the damper provides a second continuous surface and substantially seals the other of the ducts from the inlet duct.