A humidifier assembly for a CPAP includes a base housing with a gas inlet configured to receive respiratory gas from the CPAP unit. The base housing includes a first connecting device located at a sidewall of the base housing and configured to directly, removably connect the base housing to the CPAP unit. The base housing also includes a second connecting device configured to be coupled to an air delivery hose. The humidifier assembly further includes a liquid storage container that is removably received in the base housing. The liquid storage container includes a liquid storage space configured to store liquid and a humidifying region configured to receive the respiratory gas from the gas feed opening and receive a partial amount of the liquid stored in the liquid storage space to enrich the respiratory gas with moisture.