Patent ID: 8555820

Claim:
A boiler comprising: a plurality of inner heat-transfer tubes arrayed cylindrically between an upper header and a lower header and making up an inner heat-transfer tube row; a plurality of outer heat-transfer tubes arrayed cylindrically between the upper header and the lower header so as to surround the inner heat-transfer tube row and making up an outer heat-transfer tube row; inner fins provided so as to project from each of the inner heat-transfer tubes on an outer circumferential side of the cylindrical inner heat-transfer tube row; outer fins provided so as to project from each of the outer heat-transfer tubes on an inner circumferential side of the cylindrical outer heat-transfer tube row; an inner row communicating portion provided in a lower end portion of the inner heat-transfer tube row, and communicating an inside and an outside of the inner heat-transfer tube row; an outer row communicating portion provided in an upper end portion of the outer heat-transfer tube row, and communicating an inside and an outside of the outer heat-transfer tube row; an inner-fin absent region that is a region where the inner fins are absent, and is provided in a lower end portion of each of the inner heat-transfer tubes and up to a portion above an upper end of the inner row communicating portion; and an outer-fin absent region that is provided in a longitudinally middle portion of each of the outer heat-transfer tubes, and is a region where the outer fins are absent, the longitudinally middle portion being arranged at a height corresponding to the upper end of the inner row communicating portion.