A heat exchanger unit comprising: a sensible heat exchanging part (103; 30; 81; 300) disposed in a sensible heat exchange area configured to receive sensible heat generated by a combustion reaction and to heat water, the sensible heat exchanging part including a sensible heat exchange pipe (32; 320) configured to receive the water and allow the water to flow therethrough to form a sensible heat flow passage through which the water flows; and a latent heat exchanging part (40; 82; 400) disposed in a latent heat exchange area, the latent heat exchanging part including a latent heat exchange pipe (42; 420) configured to receive the water and allow the water to flow therethrough, wherein the latent heat exchange area is located downstream of the sensible heat exchange area based on a first reference direction that is a flow direction of combustion gas generated during the combustion reaction, the latent heat exchange area being configured to receive latent heat generated during a phase change of the combustion gas and to heat the water, wherein the latent heat exchange pipe includes a plurality of latent heat straight portions extending along a second reference direction perpendicular to the first reference direction, the plurality of latent heat straight portions (8211; 421, 422) being arranged to be spaced apart from each other along a third reference direction perpendicular to the first reference direction and the second reference direction and configured to form a latent heat flow passage through which the water flows and that is connected to the sensible heat flow passage, wherein interior spaces of the sensible heat straight portions (321-323; 811) and the latent heat straight portions are formed to be long and narrow such that widths in the third reference direction are smaller than lengths in the first reference direction, characterized in that the sensible heat exchange pipe includes a plurality of sensible heat straight portions extending along the second reference direction, the plurality of sensible heat straight portions being arranged to be spaced apart from each other along the third direction and configured to form the sensible heat flow passage through which the water flows, wherein for interior spaces of the straight portions, values obtained by dividing widths in the third reference direction by lengths in the first reference direction are referred to as aspect ratios, and wherein the aspect ratios of the latent heat straight portions are smaller than the aspect ratios of the sensible heat straight portions. a sensible heat exchanging part (103; 30; 81; 300) disposed in a sensible heat exchange area configured to receive sensible heat generated by a combustion reaction and to heat water, the sensible heat exchanging part including a sensible heat exchange pipe (32; 320) configured to receive the water and allow the water to flow therethrough to form a sensible heat flow passage through which the water flows; and a latent heat exchanging part (40; 82; 400) disposed in a latent heat exchange area, the latent heat exchanging part including a latent heat exchange pipe (42; 420) configured to receive the water and allow the water to flow therethrough, wherein the latent heat exchange area is located downstream of the sensible heat exchange area based on a first reference direction that is a flow direction of combustion gas generated during the combustion reaction, the latent heat exchange area being configured to receive latent heat generated during a phase change of the combustion gas and to heat the water, wherein the latent heat exchange pipe includes a plurality of latent heat straight portions extending along a second reference direction perpendicular to the first reference direction, the plurality of latent heat straight portions (8211; 421, 422) being arranged to be spaced apart from each other along a third reference direction perpendicular to the first reference direction and the second reference direction and configured to form a latent heat flow passage through which the water flows and that is connected to the sensible heat flow passage, wherein interior spaces of the sensible heat straight portions (321-323; 811) and the latent heat straight portions are formed to be long and narrow such that widths in the third reference direction are smaller than lengths in the first reference direction, characterized in that the sensible heat exchange pipe includes a plurality of sensible heat straight portions extending along the second reference direction, the plurality of sensible heat straight portions being arranged to be spaced apart from each other along the third direction and configured to form the sensible heat flow passage through which the water flows, wherein for interior spaces of the straight portions, values obtained by dividing widths in the third reference direction by lengths in the first reference direction are referred to as aspect ratios, and wherein the aspect ratios of the latent heat straight portions are smaller than the aspect ratios of the sensible heat straight portions.