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.