The previous owner disconnected the ducting to the living room.
There are enough other registers that feed the living room. All other
registers have air and the house air conditioning seemed fine.
Is this as simple as the new buyer removing the ducting and plugging up the
hole in the garage wall…or does this customer need a HVAC contractor.
It wouldn’t fly in our area.
Too cold in the Winter 
Tha’st a pretty good sized disconnected duct.
Each room is required to have a heat source and from you description one doesn’t.
Report what you see and move on.
Am I correct this passes through the firewall between the garage and home? Looks like a serious breach to me! Imagine the draft/backdraft through that vent!
Thanks…I think I found the language to recommend a HVAC contractor
with out being to being too threatening.
Another note: would the size of the garage support the combustion air requirements of the 2 appliances??? Something to think about.