Often used in the hospitality industry, a PTAC is a self-contained air conditioner installed through-the-wall of rooms with an outside wall. One PTAC is installed for each room, and the occupant of each room can control the temperature of that room independently from other rooms. Some PTAC units include an optional heating unit as well.
Because PTAC units are typically installed in rooms with a wall leading directly to the outside, they don't require ductwork, which can substantially reduce both installation cost and the amount of space needed for installation. However, they are typically less efficient than central air conditioning systems, which increases their cost over time.
Moderate climates are best suited for PTAC Air Conditioners. Severe cold or hot weather will overwork the unit, compromising its efficiency.
Purchasing can be costly if buying several units at a time to heat/cool the entire house. PTACs are often noisier than comparably powerful mini-split air conditioners.