A heat exchanger including a first header, a second header, and a third header. The third header includes a first plate including a generally planar face and a second plate including a generally planar face parallel to the planar face of the first plate and joined to the planar face of the first plate. The second plate includes an arcuate recess that extends from the planar face of the second plate to at least partially define a flow conduit between a first tube and a second tube. The arcuate recess has a radius of curvature measured from an axis generally parallel to the planar faces of the first and the second plates, and the axis is located within a first plane generally parallel to and midway between first and second opposing flat broad sides of the first tube and the second tube.