A heat exchange system includes a first flow passage and a second flow passage. The heat exchange system is configured to transfer heat between a first fluid flowing through the first flow passage and a second fluid flowing through the second flow passage. The first flow passage includes an inlet header, a plurality of tubes, and an outlet header. The inlet header includes a plurality of header-tube transition portions configured to allow the first fluid to flow from the inlet header and into the tubes, the plurality of header-tube transition portions each including a smoothly curved inlet portion and a tapered tube connection portion.