A heated breathing circuit detection system (80) verifies the proper set up and connection of a breathing circuit (21) to a heater unit (18) of a humidification system. The detection system automatically detects that the breathing circuit (21) is connected to the heater unit (18), and the nature of the heating circuit(s) (34, 36) thereof. In one embodiment, the resistance of the heating circuit(s) (34, 36) is determined and compared to an expected resistance or range of acceptable resistances to determine if the heater circuit(s) is properly or actually attached and properly operating. The humidification system also has the ability to determine the delivery mode of the breathing circuit, i.e., whether a single inspiratory limb (22), or both inspiratory and expiratory limbs (22, 24), is connected to the heater unit (18).
