An apparatus (100) for delivering gas to a patient comprising a gas delivery device (104) configured to provide gas at a predetermined pressure level, a heater (106), operable to heat the contents of a water chamber installable in proximity to said heater (106), the chamber having an inlet and an outlet, said inlet configured to receive gas from said device (104), a controller or processor configured to energise said heater (106) according to at least a user selectable level, a removable cover, wherein, in use, when said water chamber is installed in proximity to said heater (106), said apparatus (100) delivers humidified gas to a patient at a predetermined pressure level via the outlet of the water chamber； and when said cover is installed, said apparatus (100) delivers unhumidified gas to a patient at a predetermined pressure level.
