Ductwork?

Ethan, it might be worth it for you to look into putting a couple of dampers in your current ductwork, in essence making the upstairs a different zone than the downstairs.

Tape all the duct work joints, pull all the nails that you can.

No ductwork needed hangs on the wall and some can be disguised as wall art (they have a picture frame might be pricey for a rental though).If your in monmouth or ocean county NJ you can call Itak Heating and cooling for more info.

Does the duct work deliver all the hot or cold air where it's intended?

If you google "REME" you will find links to a company called RGF that sells products that go in the duct work or plug in to the wall.  

.- $275.00 Clean Ductwork- $93.19 Clean Walls- $52.28 Clean & Deodorize Carpet- $33.40 Ozone treatment That as just for the master bedroom, I won't go over everything, but the quote broke it down by room.

If there are visible signs of something you perceive to be mold, get the duct work professionally cleaned before you fire it up as well.

He resided with his parents who were unaware (until winter) that his habit was to empty his colostomy bags into the ductwork in his room.

You'd have to be getting a great deal so you could do an every surface rehab and new duct work for the hvac.