zoning is possible but problematic
YOU COULD ADD A ZONE TO YOUR EXISTING SYSTEM BUT IF IT IS A SMALL ADDITION YOU MIGHT JUST ADD A DUCT IF YOUR UNIT COULD HANDLE THIS. THE PROBLEMS YOU COULD HAVE IS THE DOWNSTAIRS, DURING THE COOL MODE, WOULD REACH DESIRED TEMP BEFORE YOUR UPSTAIRS AND THE UNIT WOULD SHUT OFF. DURING THE WINTER YOUR UPSTAIRS MAY GET TOO HOT WHILE REACHING DESIRED TEMP DOWNSTAIRS. IF YOU INSTALL A SECOND ZONE WITH MOTORIZED DAMPER AND AN UPSTAIRS T-STAT YOUR ADDITION DUCTWORK PROBABLY WILL NOT DUMP ENOUGH AIR TO KEEP THE FURNACE FROM OVERHEATING AND WOULD REQUIRE A GRAVITY BYPASS
AND AN ADDITIONAL DUMP AREA DOWNSTAIRS.
GET A COMFORT ADVISOR. GOOD LUCK