My unit is approx. 16 years old and on its last leg. The tag on it is worn so badly that you can't get any information on its size or anything else. I can't even tell what make/model it is. My house is approx. 1500 sq. ft. with a tray/vaulted ceiling (no attic) upstairs which makes for more sq. footage to be heated/cooled. What size unit should I replace this one with? Also, what size ducts should I have coming into the house to support the new unit? Any assistance is greatly appreciated.