The present disclosure pertains to a pressure support system configured to provide pressure support therapy to a subject, wherein the pressure support system is configured to determine a volume of liquid held by a humidifier. The liquid volume determination is based on the temperature of the liquid in the humidifier, the temperature of the heater in the humidifier, and/or the temperature of a component of the heater (e.g., a heating element), subsequent to modulation of the rate at which energy is dissipated into the liquid by a heater. Applying a known amount of energy for a known amount of time (power) increases the temperature of the liquid in the humidifier. The amount of liquid in the humidifier can be determined from the applied power and the rise in liquid temperature, heater temperature, and/or heater component temperature over time because the rise in liquid temperature over time is proportional the volume of liquid in the humidifier.
