Abstract: A manifold having multiple chambers for use in a cross-counterflow heat exchanger assembly includes a first member having arms extending from a base to arm ends. A second member is secured to the first member to define the manifold. The second member includes an inner plate edge that defines a first mating surface that extends inwardly along the inner plate edge from each of the plate ends to mate with arm ends. A wall extends transversely to the inner plate edge to a wall end. The wall end mates with an inner base surface to divide the interior of the manifold into a plurality of chambers. At least one lip extends transversely to the inner plate edge to define a second mating surface that extends perpendicularly from the first mating surface and mates with an inner arm surface of the arms.