A HEAT EXCHANGER

摘要

A condensing boiler (1) comprises a heat exchanger (5) having a cylindrical first heat exchange wall (6) surrounded by an outer water chamber (10). A plug (17) extends into the first heat exchange wall (6) and forms a combustion chamber (22) and an annular downwardly extending flue gas passageway (23) for accommodating flue gases from the combustion chamber (22). The plug (17) comprises an outer shell (18) which forms a second heat exchange wall (19) and an inner cylindrical shell (35) which forms with the outer shell (18) an inner water chamber (36). A connecting pipe (46) connects the inner water chamber (36) to the outer water chamber (10) so that water flows in series through the inner water chamber (36) and the outer water chamber (10) from a return water inlet (42) in the inner water chamber (36) to a flow water outlet (16) from the outer water chamber (10).