A tube transition fitting includes a body having a scalloped end having a raised portion and a depressed portion connected by a continuously sloping transition portion. The fitting is formed having a first wall thickness and a second wall thickness. A tube seat is formed on a surface connected to the body, the surface being adjacent a transition from the first wall thickness to the second wall thickness. A tube transition assembly includes a header portion, the tube transition fitting, and a heat exchange tube, each being connected using one or more simplified and/or heat-optimized connections.