A humidifier system for heating and humidifying respiratory gases has a housing with an inner chamber, a first port at the first end for connection to a ventilator breathing circuit and a second port at the second end for connection to a patient to supply respiratory gases to the patient and to receive exhaled gases from the patient. A body of heat moisture exchange (HME) material is located within the chamber, and a water permeable device is also located within the chamber. The housing has a water refill inlet communicating with the water permeable device. A water supply outside the housing is connected to the water refill inlet to supply water to the water permeable device. A heater mounted outside the housing supplies heat to the housing and maintains the housing at a selected temperature.