ABOUT THIS SYSTEM: Mix & Match Wall Mount and/or Ceiling Cassette for your custom system. Please select from below each of the indoor units. It is not required to use all five zones. The sum of the total indoor BTUs can not exceed 58K. Example: 9+24+24=57K BTU (suitable), 7+9+9+15+18=58K BTU (suitable), 7+12+12+12+18=61K BTU (NOT suitable).