Provided are systems for humidifying gas delivered to a patient. A humidifier unit (107) is provided located proximal to a patient interface (105) of a patient circuit (103). The humidifier unit includes a chamber that receives water from a water source (109), a heat source disposed within the chamber, a water flow sensor (113), an output temperature sensor (117), an output humidity sensor, and/or other sensors. A controller (119) receives flow data relating to water being provided to the chamber and temperature data relating to the temperature of the humidified gas, humidity, and/or other data. The controller further adjusts a flow of water being provided to the chamber based on the flow data and/or a heat output of the heat source based on the received data.