[sourdough]

If you haven't removed the exterior exhaust and it's the only thing on the exterior wall from the furnace you probably should give that a try. I've had one (a year old) that was stuck so tight in that tube that I almost had to bend it up trying to get it off. Rocking and twisting finally got it to break loose. That will be hard to do trying to use the furnace to twist. I'm sure if it that tight it would feel like it was stuck.