Stove Install Retro Fit

I am taking out an old Franklin stove and putting in a new Jotul Castine. One story house going straight up through the attic and out the roof. The old stove used 10 inch pipe up to the ceiling support box and then 10 inch inside diameter chimney pipe (looks to be 14 or 16 inch outside diameter). The new stove calls for 6 inch pipe. I am trying to avoid taking down the old ceiling support box which has a built in trim piece and an 18 inch diameter hole through the ceiling.

I talked to northline express and they said the only way to do it is remove the old ceiling support box, patch the plaster, and then install and frame a new ceiling support box. Can anyone think of a way to avoid taking down the old ceiling support box?

Also, any way to run the new 6 inch chimney pipe up the old 10 inch chimney pipe so I don't have to mess with the roof flashing? Is there a way to seal up the roof flashing for a 10 inch chimney pipe around a 6 inch chimney pipe?

Should I just rip it all out and start from scratch? Any ideas would be greatly appreciated. Thanks!

Thanks begreen, I'll take your advice on that. It's a big investment to not just pay a couple hundred dollars extra to do it right.

No idea. It went from oval to round

Totally agree. Thanks for the input mellow.

I burned in it for a year which was plenty long enough. Some nights I didn't sleep great worrying about things.

I am thinking of doing the install myself as it is just straight up. Now that I've made the decision to rip out the old system, my only hold up now is the hole in the roof (which is a 21.5" by 20" oval) and the size of the old chimney flashing compared to the new flashing. I'm worried the new flashing wont be large enough to get under enough shingles and still be centered.

Thanks mellow. I'll search around and see what I can find. The old system is all dura vent so I am going to contact them about running a 6inch chimney through a 10 inch chimney flashing and see what they say. I would think if the storm collar were big enough to cover the opening, it could be pushed down tight enough that it would seal everything up once caulked. That may be wishful thinking though.