The home was a townhouse on a slab built in 1993. 2 story home
Downflow furnace. In slab ducts.
What is the large diameter pipe for in the closet? Return is above, supply is in the slab. No fresh air intake but it had louvered doors. Would this be the supply for the 2nd floor. Seems oversized.
There were also some flex pipes in the garage attic and I could not tell were this one pictured terminated.
You probably do not have enough info from the pics but I was not sure the purpose of the large diameter pipe.
I did make a note of the condensate pipe that was loose/leaked and had a lot of elbows.