Amazon.com, Home Depot and Lowe's sell ductless air conditioners. These mini-split and multi-split units offer cooling for a single room or the whole home without installing bulky ductwork in the floors, walls or ceilings.
Ductless air conditioners have an outside compressor unit similar to the compressor used with a central air conditioning system. However, instead of using a central air handler, they have one or more air handlers in the rooms they cool. The liquefied coolant travels to the air handler through pipes, evaporates to provide cooling and then travels back to the compressor through another set of pipes. Installation requires drilling small holes in the structure through which these pipes travel.
While these systems are more expensive than window air conditioners, they offer several advantages. By leaving the windows free of an air conditioner, occupants have the opportunity to open them for natural ventilation on days when they do not want to operate the system. Since the compressor is located away from the air handler, ductless systems are quieter when in operation. The only noise inside the home is that of the quiet blower located in the air handlers.
Some ductless systems also offer heating using a heat pump. The heat pump is more efficient than resistance heating in homes where electricity is the only option.