If you don't like unknowns,,,you're in the wrong business. Open up the ceiling and get r done
Exactly!!!
I've done many of these, be prepared for the worse!
Helpful info (Not going to list all the scenarios):
1. The ducting is most likely a 3". Buying a fan with the same size fit makes things easier.
2. If the ducting is too short, you can buy extensions, and extend the old.
3. I've only done two with no damage--if no access from above. Make sure you inform the customer in writing that there may be damage.
4. If the wire is too short, try removing the staple--you my have an additional 6-12 inches to work with. If you don't, then turn the fan--with the electrical knock-out facing the wire. Note: In some cases this will also turn your venting duct away--which could lead to other problems.
Moving the fan a few inches will help greatly in most cases, so I would plan on having drywall damage. If they have Plaster, then get ready for more challenges!