So, it turns out that one of the bedrooms in our new home (which is 27 years old) is not connected to the HVAC system. There's a vent there, duct work in the walls, but they never bothered to connect it to the main line.
So, they're going to find a way to rig it through my attic to save money and not rip my walls apart, but somehow that was not addressed in nearly 30 years.
Mind boggling.