I have this unit, in the heat pump model, close the the return duct for the central system in a 1800sqft single level home..The central fan is set to circulate the air 30% an hour. It keeps the house cool or warm unless it gets above 95 or below 30 outside, in which the central system is set to turn on.  It has more than paid for itself in the money saved on electric and especially gas normally used by running the central system by itself. Three years running daily and no problems.