A humidifier tub includes a first side having an air inlet opening configured to receive the pressurized flow of respiratory gas. A second side opposes the first side. An air outlet opening is configured to discharge the pressurized flow of respiratory gas with added humidity. An inlet passage extends from the air inlet opening toward the second side so that the pressurized flow of respiratory gas travels through the inlet passage in a first direction. A guidance structure is located between the first and second sides and positioned so that a traveling direction of the pressurized flow of respiratory gas changes from the first direction to a second direction upon the pressurized flow of respiratory gas engaging the guidance structure. The guidance structure extends downward from a lid. In addition, the first direction is a lateral direction and the second direction is a downward direction.