These fan units are made especially for free-standing cabinets. They are installed into the base, top cover or door of the cabinet as required. A fan unit for free-standing cabinets - it is installed into the top cover from outside of the cabinet, into the bottom from inside of the cabinet. It is necessary to use the installation frame of the bottom fan unit when installing into the base of the cabinet - RAB-CH-X21-A1 which is mounted using a two-sided gluing tape.