I have a 1/2 bathroom next to my heater. The previous owner dropped the ceiling 6" and ran a 3" pipe to the middle of the room. Dropped a vent down then continued to heat the full bath above. I removed the pipe. I plan on installing a new 3" pipe with a T junction, continue to the end of the joist run a 90 degree vertical then 90 degree to up and to the left for the upstairs bath. I will buldhead this in and put a round vent cover in the bulkhead at the T.
Red is vent I will replace. Circle is the vent for the room. Blue is the bulkhead.