Add Second Zone or Room Split system(s)?

[ceebee44]

Three story home (finished basement) that was incorrectly sized with a single zone unit. Has always been freezing in large finished basement and 10-15 degrees hotter in upstairs bedrooms and hallway - compounded by open floor plan and cathedral ceilings. Economically it is a waste - a unit that runs constantly and only dispatches cold air up three stories in small amounts.

Have been suggested Mitsu split slim system as a solution for the master bedroom since the other three bedrooms are currently less used with college kids. Question is about cost and value - at what point does a traditional second zone system with unit in attic and new ceiling vents , etc. make more sense than multiple split systems? The single system will clearly handle the heat issues in the MBR, but leave the rest of the upstairs hot and adding a unit to another bedroom(s) would involve more cost and would require a multi-capable system out the gate.

Is there an advantage to these split systems, especially as the costs approach a traditional second zone retrofit?

[George2]

Depending on your ductwork layout, it might be easier to put in a three (or 4)zone damper system.

As an example, it may be able to give you a thermostat for every level.