A respiratory apparatus is configured to deliver breathable gas to a patient's airways and includes a flow generator configured to pressurize the breathable gas and a humidifier configured to vaporize water and deliver water vapor to humidify the breathable gas. The respiratory apparatus further includes a gas flow path leading from the flow generator to the humidifier and from the humidifier to a patient interface. A continuous heater is positioned within the gas flow path and includes multiple separately controllable heating zones.