I tore out the old bathroom fan unit today and discovered a new problem: hard metal ductwork that is 3" in diameter. The connector is 4" in diameter. It ends just at the edge of the hole.
I cannot just put the new plastic connector around the old and tape it because it has a flap inside that won't open/close the vent when the fan is on in that configuration. The 3" duct blocks that flap.
I cannot easily just replace all of the ductwork since it appears I'd be up on the roof - see the photo of the pipe exiting the attic interior.
The metal is heavy duty rigid stuff, so cutting it seems to be a lost cause, too.
Is it time to call in a pro? Or is there a workaround within my reach? (Move the hole 5-6" towards the tub so I can install an adaptor, then patch the gap in the ceiling?) Right now, the tub-side edge of the hole is 12" from the outside of the tub area.
Photos are here