Hello! I’m hoping some of you pros can answer a few questions about a flue vent pipe issue. We have a condo unit in 70+ year old building. The pipes in pic below attach to the hot water flues that come up from the basement and vent out the attic roof. One of them dislodged during the course of a roof replacement. When the workman went back into attic to reposition the pipe, they realized that the pipe measures short and apparently, was originally mounted on top of a mortar bed to compensate for being cut too short. Over time , the mortar cracked and gave way. It also appears as if a second pipe has mortar at the base that is beginning to crack as well. So my questions are—can a new galvanized metal pipe be used in place of the old pipe (that is probably asbestos) that gave way? Given the rectangular shape of the flue, how should a rectangular to round transition be done? Can the mortar on the base of the other pipe be reinforced to shoulder that be replaced as well? Two HVAC companies have told us to find a chimney company to repair—is this correct? Any other issues we should know about? Thank you in advance for your expertise!