A heat exchanger and a method for additively manufacturing the heat exchanger are provided. The heat exchanger includes a housing defining a heat exchange plenum having a first fluid inlet and a first fluid outlet separated along a transverse direction. A plurality of heat exchange banks pass through the heat exchange plenum between a top side and a bottom side of the housing substantially along a vertical direction, each of the heat exchange banks comprising a plurality of heat exchange tubes. A plurality of collector manifolds are positioned at the top side and the bottom side of the housing, each collector manifold defining one or more connecting ports providing fluid communication between adjacent heat exchange banks.