Room air conditioners are encased assemblies designed primarily for mounting in a window or through a wall. They are designed to deliver cool or warm conditioned air to the room, either without ducts or with very short ducts (up to a maximum of about 48 in. [1220 mm]). Each unit includes a prime source of refrigeration and dehumidification and a means for circulating and filtering air; it may also include a means for ventilating and/or exhausting and heating. PTACs are designed primarily for commercial installations to provide the total heating and cooling functions for a room or zone and are specifically for through-the-wall installation. The units are mostly used in relatively small zones on the perimeter of buildings such as hotels and motels, apartments, hospitals, nursing homes, and office buildings. In larger buildings, they may be combined with nearly any system selected for environmental control of the building core. This chapter discusses design and application of both types of systems. ROOM AIR CONDITIONERS Sizes and Classifications Design Performance Data Special Features Safety Codes and Standards Installation and Service PACKAGED TERMINAL AIR CONDITIONERS Sizes and Classifications General Design Considerations Design of PTAC/PTHP Components Heat Pump Operation Performance and Safety Testing