A pressure support system configured to provide pressure support therapy to a subject is described. The pressure support system comprises a humidifier configured to control the humidity of gas provided to the subject during a sleep cycle to ensure an amount of liquid will remain in the humidifier at the conclusion of an estimated usage time. The pressure support system is configured to ensure humidified breathing gas is delivered to a subject during a usage time within a pressure support usage period. During times when the subject's moisture demand is greater than amount of moisture available in the humidifier, the pressure support system may decrease the amount moisture in the breathing gas so humidified therapy is available during the entire time the user is asleep.