Abstract: A heat exchanger, a reinforced header assembly for use in a heat exchanger, and a method of assembling a heat exchanger. The reinforced header assembly may include a header connectable with a tank to define a collection tank assembly, the header including a central portion defining a plurality of header openings, and a connecting portion connectable to the end of the tank wall such that the tank portion and the header cooperate to define the collection tank assembly, the connecting portion including a wall extending at a non-parallel angle relative to the central portion, and a reinforcement member including an inner portion defining a plurality of member openings, and an outer portion extending at a non-parallel angle relative to the inner portion, the outer portion being complementary to and connected to at least a portion of the wall of the connecting portion of the header.