A heat exchanger unit comprising: a combustion chamber in which a flame caused by a combustion reaction is located; a heat exchanger for a condensing boiler, the heat exchanger being located under the combustion chamber , wherein the heat exchanger includes heat exchange pipes configured to receive heat generated by the combustion reaction and to heat heating-water flowing through the heat exchange pipes and a main case having the heat exchange pipes accommodated in an interior space thereof; and a combustion chamber heat insulation pipe disposed adjacent to the combustion chamber and configured to receive the heating-water and allow the heating-water to flow therethrough to thermally insulate the combustion chamber , characterized in that : wherein the combustion chamber includes a combustion chamber case configured to form an interior space in which the flame is located and a combustion chamber flange protruding outward from a lower end of the combustion chamber case , wherein the heat exchanger for the condensing boiler further includes a heat exchanger flange protruding outward from an upper end of the main case , the heat exchanger flange being coupled with the combustion chamber flange , wherein the combustion chamber and the heat exchanger for the condensing boiler are coupled by a brazing connection formed by of applying and heating a paste, and the paste being provided between the combustion chamber flange and the heat exchanger flange . a combustion chamber in which a flame caused by a combustion reaction is located; a heat exchanger for a condensing boiler, the heat exchanger being located under the combustion chamber , wherein the heat exchanger includes heat exchange pipes configured to receive heat generated by the combustion reaction and to heat heating-water flowing through the heat exchange pipes and a main case having the heat exchange pipes accommodated in an interior space thereof; and a combustion chamber heat insulation pipe disposed adjacent to the combustion chamber and configured to receive the heating-water and allow the heating-water to flow therethrough to thermally insulate the combustion chamber , characterized in that : wherein the combustion chamber includes a combustion chamber case configured to form an interior space in which the flame is located and a combustion chamber flange protruding outward from a lower end of the combustion chamber case , wherein the heat exchanger for the condensing boiler further includes a heat exchanger flange protruding outward from an upper end of the main case , the heat exchanger flange being coupled with the combustion chamber flange , wherein the combustion chamber and the heat exchanger for the condensing boiler are coupled by a brazing connection formed by of applying and heating a paste, and the paste being provided between the combustion chamber flange and the heat exchanger flange . wherein the combustion chamber includes a combustion chamber case configured to form an interior space in which the flame is located and a combustion chamber flange protruding outward from a lower end of the combustion chamber case , wherein the heat exchanger for the condensing boiler further includes a heat exchanger flange protruding outward from an upper end of the main case , the heat exchanger flange being coupled with the combustion chamber flange , wherein the combustion chamber and the heat exchanger for the condensing boiler are coupled by a brazing connection formed by of applying and heating a paste, and the paste being provided between the combustion chamber flange and the heat exchanger flange . <EOS>