Since no one else seems to want to take a shot at this, I'll bite.
If you are talking a clean sheet of paper here, you might consider
PTACs (the motel type heat /air units) they do a great job, once the
room is sleeved and wired for them you can service, upgrade and replace
fairly easily. As to brand, the usual suspects, Carrier, Trane, etc. I
have a 2 story addition that is totally PTAC, one on each floor, and it
heats and cools cheaply and effectively, the only drawback is; the area
directly in front of the unit about 10' out isn't usable for sitting
unless you like brain freeze or are experiencing hot flashes.
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