So I occupy a space that has an HVAC system that hasn't functioned in years. It needs to be completely replaced and every specialist that has come in to see it has basically quoted the landlord about $50k + to fix it. The landlord has no intention of making that repair so we have vents running through the entire 13k sq ft space that are not in use and probably never will be. My room in this space does not have a window but I would like to install a portable AC. My question is - since the vents are not in use - can I exhaust the portable AC into the unused vents? Bigger question - are there any other options to cool the larger subdivided spaces of the building - one space is 2400 sq ft and another is 1000 sq ft. I've looked at large portable AC units but not sure if it would work. Any thoughts would help. Thanks

We moved the old and have a new oil burner, the plenum size is 24x24, the burner calls for a 16x25 filter rack, but the existing return is 8x16, can we transition to this size with duct, to a 14" flex, or leave 1/2 open to basement and the other half pulling from 8x16 ? Is it choking it down too much ?