An air duct for installation in a passenger compartment of a vehicle includes duct walls defining the cross-section of the air duct, such as a top duct wall and a bottom duct wall. The bottom duct wall may contain a fixing hole, whereas the top duct wall may contain an access hole. The air duct may be fixed directly to the vehicle body by a fastener, such as a screw, through the fixing hole in the bottom duct wall. To prevent air from escaping through the fixing hole, an outer wall of the bottom duct wall may be shaped at least in the area of the fixing hole so that it lies flush with and essentially air-tight against the vehicle body. After attachment, the access hole may be suitably sealed to prevent air from escaping.