Most draft beer keg refrigerators are not designed for being built into cabinet. Those that are designed for built-in use usually have built-in fans, and vents to the front of the unit, which help dispel the heat that is generated by the refrigerator compressor.
Keg refrigerators that are not designed for built-in use can be put in cabinets. But, it must be kept in mind that space is required for air circulation to dispel the heat that is generated by the refrigerator compressor. Without adequate space air circulation, the compressor will be unable to properly cool the inside of the refrigerator, and the compressor will likely overheat and burnout.
When determining how much space air circulation is required, it is recommended to refer to the refrigerator manufacture’s recommendations for specifics. If nothing is specified, it is recommended to leave at least a 3" space on all sides of the refrigerator for circulation. This is particularly important in hotter climates.