Abstract: An apparatus for compensating heat and humidity loss in a device that administers or restitutes air to a patient, amongst others in a device that comprises an air supply duct which extends between a respirator or an anaesthesia apparatus and the patient. The apparatus includes a housing with a coupling to be connected on this air supply duct, in which coupling a heating resistance is mounted, in which housing water is admitted. Further included in the housing is a membrane with water impermeable but water vapor permeable characteristics and an element that assures the desired heat level, in the coupling and air supply duct.