A heat exchanger has a core comprised of at least one core section defined by a plate stack comprising a plurality of core plates, each core plate having a plurality of spaced apart, raised openings surrounded by a flat area. The raised openings of adjacent plates are sealed together to define a plurality of tubular structures. Top and bottom manifolds are sealed to the top and bottom of the core, with continuous top and bottom end plates providing structurally rigid connections between multiple core sections of the heat exchanger. The heat exchanger may have numerous configurations, including stepped core, curved core, angled core, and/or a core having multiple sections of the same or different length, while minimizing the number of unique parts and/or parts of complex shape.