Class A chimney transition to existing masonry?

[Bcomish]

I’ve been trying to figure out a way to have a wood stove installed in our house. The problem is the flue of the existing masonry chimney is 5”. Originally was thinking about an insulated oval liner but that is cutting it close and not even sure if it would fit. The caveat to the size of the flue we have is that it opens up as it gets close to the roof and based on the size of the bricks I would say toward the roof the size of the flue flares to about 8”(it’s plenty wide, at least 20”). My idea is this: could I run class A chimney up alongside the interior chimney, through the 1st and 2nd floor and then when I reach the attic and where the chimney opens up tie into the existing chimney with an insulated liner? It’s a historic house and the chimney is part of the aesthetic of the house so really don’t want to tear it down. Last picture shows how the chimney gets larger as it approaches the roof line.

 

[begreen]

Given it's age I assume there is no clay liner. Can you determine how soon it becomes a little larger, like 5.5" or 6"? If it's a short distance then maybe .5" can be shaved off each side to clear an oval insulated liner.

 

[Bcomish]

Given it's age I assume there is no clay liner. Can you determine how soon it becomes a little larger, like 5.5" or 6"? If it's a short distance then maybe .5" can be shaved off each side to clear an oval insulated liner.

It looks like it goes all the way down at 5” and only gets larger at the top where it exits the roof. My guess is the last 3 ft before it exits is where it gets larger.

 

[begreen]

6" oval Duraliner is 4 3/4" but it sounds like that may not make it if there are any mortar globs blocking.

 

[Bcomish]

6" oval Duraliner is 4 3/4" but it sounds like that may not make it if there are any mortar globs blocking.

Would I be good to run the class A up until the chimney gets bigger and then just run an insulated liner down to that point and tie into the class A? Not finding much where this is done but can’t think of why it wouldn’t be ok or up to code.

 

[begreen]

I won't say no, but I haven't seen it done. Perhaps bholler has. FYI, there are no 45 or 90º class A elbows sold in the US. 30º is the largest angle.