I need to remove the existing ductwork in my basement to install insulation behind it. I'd like to do it without destroying the ductwork. The vertical duct is right against the foundation, so I can't pull it off the end of the pipe:

What's the easiest way to do this? On the other end of the horizontal duct, it goes into the top of the main trunk, so it's not any easier to disconnect on that side. Do I just need to suck it up and hacksaw through the round duct, and replace the cut piece?