BTU (British Thermal Units) –is a unit of energy used in the heating and air-conditioning industries. The larger area you need to cool or heat, the more BTUs you need. For single zone systems it is pretty straight forward but for multi zone systems, the indoor units and outdoor units have a set number of BTUs.
What makes ductless great is that each indoor unit runs independent from the rest so the total number of BTUs for the indoor units can be up to 30% greater than the outdoor unit’s BTU.