A respiratory apparatus for providing a humidified flow of pressurised breathable gas to a patient, comprising: a flow generator to generate a flow of pressurised breathable gas to be delivered to a patient; a pressurisable humidifier chamber including a chamber inlet configured to receive the flow of pressurised breathable gas from the flow generator , the chamber having a rear wall comprising a chamber outlet , wherein a heating plate is positioned at the bottom of the chamber ; a humidifier lid being hingedly attached to a wall of the chamber and pivotably movable between an open position and a closed position, an inside surface of the humidifier lid having a rim ; a water tub configured to contain a supply of water, the tub having a tub base which adapted to contact the heating surface, a tub lid , and a tub seal sealing between the tub base and the tub lid , the tub lid having a tub inlet and a tub outlet, the tub outlet being provided on a rear wall of the tub and configured to deliver the flow of pressurised breathable gas with added humidity to the chamber outlet , the tub being constructed and dimensioned to be positionable within the chamber ; and a chamber seal configured to seal the chamber such that the flow of pressurised breathable gas pressurises the chamber when the tub is within the chamber and the humidifier lid is in the closed position, the chamber seal having a groove configured to receive the rim of the humidifier lid , the chamber seal having a sealing rim that extends around a perimeter of the chamber seal , the sealing rim configured to seal the humidifier lid when the humidifier lid is in the closed position. a flow generator to generate a flow of pressurised breathable gas to be delivered to a patient; a pressurisable humidifier chamber including a chamber inlet configured to receive the flow of pressurised breathable gas from the flow generator , the chamber having a rear wall comprising a chamber outlet , wherein a heating plate is positioned at the bottom of the chamber ; a humidifier lid being hingedly attached to a wall of the chamber and pivotably movable between an open position and a closed position, an inside surface of the humidifier lid having a rim ; a water tub configured to contain a supply of water, the tub having a tub base which adapted to contact the heating surface, a tub lid , and a tub seal sealing between the tub base and the tub lid , the tub lid having a tub inlet and a tub outlet, the tub outlet being provided on a rear wall of the tub and configured to deliver the flow of pressurised breathable gas with added humidity to the chamber outlet , the tub being constructed and dimensioned to be positionable within the chamber ; and a chamber seal configured to seal the chamber such that the flow of pressurised breathable gas pressurises the chamber when the tub is within the chamber and the humidifier lid is in the closed position, the chamber seal having a groove configured to receive the rim of the humidifier lid , the chamber seal having a sealing rim that extends around a perimeter of the chamber seal , the sealing rim configured to seal the humidifier lid when the humidifier lid is in the closed position. <EOS>