Abstract: An air-to-air heat exchanger for pre-cooling and humidifying a breathing gas supplied to a patient. The air-to-air heat exchanger is made of low specific heat material and has an elongate conduit, a plurality of interior fins and a plurality of exterior fins. The elongate conduit is installed adjacent the output of an inspiratory lumen, through which a breathing gas is supplied to a patient. The interior fins extend from an inner surface toward a central axis of the elongate conduit, while the exterior fins extend radially outwardly from an outer surface of the elongate shell.