A method of building a heat exchanger includes forming the heat exchanger with layer-by-layer additive manufacturing. A first hollow annulus is formed. A body of the heat exchanger is formed to be integrally connected to and grown upwards from the first hollow annulus. The body includes an exterior wall and a heat exchanger core disposed within the exterior wall. The body defines an interior that is cylindrically shaped with an axis oriented parallel to a direction of gravity. The first annulus is disposed on a gravitational bottom of the body. A second hollow annulus is formed integrally connected to and grown upwards from a gravitational top of the body. Residual powder is removed from a bottom of the heat exchanger.