A heat exchanger tube bundle of horizontal gas path design is presented, the tube bundle comprising a sequence of bottom headers and corresponding top headers, wherein each unit of the sequence comprises a row of tubes, wherein each bottom header-is fluidly connected to a corresponding top header-via at least two similar tube rows for passing a fluid in a first direction between the bottom header and the top header, respectively, and wherein each unit of the sequence further comprises at least one further tube row in fluid connection with one of said bottom or top header, wherein the further tube row is further fluidly connected to a header of a subsequent unit, and wherein the further row's tubes are configured for passing the fluid in a second direction opposite to the first direction. Moreover, a related heat recovery steam generator-and combined cycle power plant are presented.