A method for manufacturing a heat exchanger includes stacking a plurality of parting sheets, a plurality of lengthwise closure bars, and a plurality of widthwise closure bars to form a rectangular first heat exchanger section. The first heat exchanger section includes at least one widthwise passage extending between a pair of the widthwise closure bars and at least one lengthwise passage extending between a pair of the lengthwise closure bars. The method also includes brazing the rectangular first heat exchanger section together and cutting a first side and a second side of the rectangular first heat exchanger section to give the first heat exchanger section a tapered-trapezoid profile. The method further includes brazing an end of a second heat exchanger section to the first or second side of the first heat exchanger section.