a humidifier and humidity sensor is disclosed for use with a breathing assistance apparatus . the humidity sensor preferably includes means to sense absolute humidity , relative humidity and / or temperature at both the patient end and humidifier end . the humidifier may also include provision to both control independently the humidity and temperature of the gases . further , a chamber manifold is disclosed to facilitate easy connection of the humidifier to various outlets , inlets and sensors . a heated conduit is described which provides a more effective temperature profile along its length .