I need to remove an old sheet metal air duct about 20 ft long that's over the ceiling of a hallway. I can get to it by working in the attic, but I'll have to cut it into pieces to get it out from under the ceiling joists. An alternative would be to tear out the ceiling of the hallway, including the 2x4's under the duct and take the duct out in one piece. I suppose that would make sense if the duct is replaced by a new sheet metal duct. However, from a DIY perspective, it would be simpler to replace the old duct by several flexible ducts.
What's the best tool and technique to use if I cut up the old duct? (A large section of the bottom of the duct rusted away from being under the swamp cooler. Cutting up the rest of it will require the same effort as cutting new sheet metal.)