High efficiency pvc venting through old

Is it acceptable to run your pvc vent on a new high efficiency unit through the old vent stack? Seems like a potential for debris/rain to fall in with no type of cap. Thoughts?


That would be acceptable in most areas except the original duct around the PVC vent would have to be sealed as any other roof penetration would

BTW that old class B double wall vent would make a nice pitch box like used on commercial roofs for refrigerant lines and electrical conduit roof penetration