If not accessible to mechanical damage or cracked, transite doesn’t pose a great hazard. It probably contains asbestos and I point that out in my report and suggest evaluation.
The biggest risk is that many jurisdictions don’t allow replacing a furnace using this flue material and removal and disposal can be a significant cost.
It appears to be a transite pipe however, that can only be verified by a lab. As for replacement, laws differ from state to state. In Illinois a homeowner in a single family dwelling can remove it and dispose of it in the garbage. However, if you’re an asbestos abatement contractor or it is a multi-family unit, you have to be licensed and dispose of it properly.:shock: