Our gas furnace intake (one of them, there are other intakes inside the house) currently comes out the side of the house but under a brick patio. It seems that the previous owner of the house extended that intake by added pipe underneath the brick patio, and enclosed in plywood from all 4 sides.
It seems that the pipe that was added did not fit properly in the pipe coming out of the wall. (Both appear to be 6" wide male end). Also there is some sagging of the brick patio, probably because part of it has the original concrete steps underneath it, and the rest doesn't.
What is the proper way to do this? Will I be able to find the right size of pipe that will fit with what's coming out of the wall?
Here the intake coming out of the wall under the patio:
Here's the run with the brick removed:
And, here's the final vent:
Please see this photo album for the rest: https://imgur.com/a/0pd42xK