Flue heat exchanger used range in the flue, generally by the heat pipe and the heat exchange box. Includes a plurality of heat exchange tube ends are respectively inserted into the upper tube plate and a lower tube plate heat exchanger tube bundle, as the air channel, a plurality of heat exchange tube bundle for flue gas flow in tube bundles, connected with the upper part of the air / into the collection box, bundle by connecting the collection box so that the air flows from the heat. Pipe for multi group bundle.