When it comes to how many indoor units needed for your ductless AC system, the general rule is one for every room to be cooled. Since these systems don’t use ductwork, they utilize multiple air handlers to push cold air directly to the room being served. Typically, you will only need one air handler per room, but the size of the air handler correlates directly with the size of the room. Larger rooms may call for a bigger air handler unit to effectively cool the entire area, while smaller rooms can utilize a smaller unit to maintain a comfortable temperature.