Humidification with hme and heated air delivery tube

A CPAP system for providing air at positive pressure for respiratory therapy to a patient, the CPAP system comprising:

• an RPT device configured to supply a flow of air at a therapeutic pressure;
• a patient interface forming a plenum chamber pressurizable to the therapeutic pressure, the patient interface including a seal-forming structure constructed and arranged to form a seal with a region of a patient's face surrounding an entrance to a patient's airways;
• an air delivery tube configured to pass the flow of air at the therapeutic pressure from the RPT device to the patient interface;
• a heat and moisture exchanger (HME) constructed and arranged to retain moisture from a flow of expiratory air from the patient, wherein retained moisture from the HME is returned to the flow of air for humidification;
• a controllable heater configured and arranged to heat the HME and/or heat incoming air to the HME;
• and
• a controller configured to adjust heating of the controllable heater to adjust the moisture returned from the HME to the flow of air for humidification.