A breathing assistance apparatus adapted to deliver humidified gases at a desired level of humidity to a patient, including a humidifier and a heated conduit (116). The humidifier includes a controller (100), which determines a parameter of gas flow rate and then the required power input (108) to the humidifier to deliver the gases to the patient at the required patient humidity. In a second embodiment, a conduit heater (116) is provided and the controller determines whether it has been correctly connected to the control. External sensors are dispensed with and thus the apparatus is simple and less bulky.
