Abstract: The humidifier module for use in a gas humidification unit has a humidification chamber and a water heating chamber separated by a water vapor permeable, liquid water impermeable membrane. Gas inlet and outlet ports are provided in the humidification chamber, a water inlet port is provided for the water heating chamber, a water inlet port is provided for the water heating chamber, and a heat exchange wall is provided on one side of the water heating chamber to receive heat from a heat source in the humidification assembly. The gas humidification assembly has an enclosure adjacent the heat source, for receiving the humidifier module, a water supply source, and a controller of the heater and water supply to the humidifier module. A sensor is provided for monitoring the level of fluid within the humidification chamber, and another sensor is provided for monitoring the level of water within the water heating chamber.