The term split unit means that the evaporator section fits into your existing forced air heat system plenum and the condensor sits outside. They are quite a different animal from a window air conditioner and are more compact than the all in one units that sit outside. Do you have a central furnace that will accomodate the cooling coils? Look at information below to decide what meets you needs the best, then decide if you will purchase through a contractor including installation, or purchase a unit and have a contractor install it. Most folks get the whole deal through their contractor.
Room air conditioners cool rooms rather than the entire home. If they provide cooling only where they're needed, room air conditioners are less expensive to operate than central units, even though their efficiency is generally lower than that of central air conditioners.
In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump.
In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.