Ductless heat pump systems are sized to meet the heating and cooling needs of individual zones in the home, which can vary greatly due to the thermal characteristics of the zone and connected zones. The good news is that there is a great deal of flexibility when it comes to sizing ductless heat pumps because they are inverter-driven, variable speed. Typically, a 1-ton (12,000 BTU/hr) ductless system will effectively serve up to 600 square feet. Even more square footage can be served, if there is a good backup system you are willing to use. The Heat Pump Store can help you with sizing specific to your primary zone(s).