A method of constructing a heat exchanger includes providing a base, and additively manufacturing a plurality of first walls substantially parallel and substantially vertical while being manufactured, wherein the plurality of first walls are spaced apart and attached to the base. The method also includes removing at least a portion of a build powder located between the plurality of first walls and attaching a parting sheet to the plurality of first walls. The method also includes additively manufacturing a plurality of second walls substantially parallel and substantially vertical while being manufactured and are spaced apart.