Mama Bear 8" to 6" and external wall install questions

[ponto11]

I have what I believe to be a Fisher Mama Bear. Dimensions are 26" tall (not including legs), 23.5" wide, and 22" front to back. Please see photos, including inside of one of the doors which says "GM" on it.

I'm installing in my house in the main living area and need to do an external wall installation. I'm installing on a raised floor (about 13") which leaves me with about 4' of vertical that I can run off the top exhaust port before I elbow out the wall. Once outside, I have about 12' until the roof is reached. I know I need 2' above 10' away from the roof once I breach the roof. I have several questions, thanks so much in advance!

1. Can I reduce the single wall interior piping from 8" to 6" near the wall (where I'll punch through) and use 6" for the exterior piping?
2. I know I need 12" of wall/ceiling clearance with the single wall piping. Can I use single wall piping inside without dramatically reducing air flow or should I switch to double wall for interior for air flow purposes?
3. The damper you see off the back of the stove in one of the photos. Anything I need to do with that? Should I cut a cold air intake into my wall near the damper?

Let's start there. Any other advise GREATLY appreciated! Thank you!!

 

[coaly]

You need to remove the barometric damper on the rear and cap it. This is a Barometric Grandma Bear III.

Single wall requires 18 inches clearance to combustible wall.

This is an unlisted stove without a UL Label. If insurance or following code in a jurisdiction that has adopted the International Family of Codes, UL Listing is required for a new installation.

It is against the National Standard (NFPA-211) to reduce from 8 to 6. NFPA allowed 1 inch reduction, ICC building code where adopted allows none.

It may physically work, but more info is needed, such as inside pipe configuration, horizontal run length, chimney height above stove top, and elevation. It will not have the maximum BTU capacity reduced, but many work ok when vented straight up, with the correct height and atmospheric conditions. Indoor layout as well as home tightness matters. The issue is smoke roll in opening doors quickly. A lot can be done to minimize the issue.

Double wall chimney would be needed, possibly double wall connector pipe inside, which is close clearance pipe, for down to 6 inch clearance. This will prevent flue temperature cooling before entering chimney.

I would not go the expense of 8 inch new chimney and not have a chimney capable of connecting to a newer stove since most require 6.

 

[ponto11]

You need to remove the barometric damper on the rear and cap it. This is a Barometric Grandma Bear III.

Single wall requires 18 inches clearance to combustible wall.

This is an unlisted stove without a UL Label. If insurance or following code in a jurisdiction that has adopted the International Family of Codes, UL Listing is required for a new installation.

It is against the National Standard (NFPA-211) to reduce from 8 to 6. NFPA allowed 1 inch reduction, ICC building code where adopted allows none.

It may physically work, but more info is needed, such as inside pipe configuration, horizontal run length, chimney height above stove top, and elevation. It will not have the maximum BTU capacity reduced, but many work ok when vented straight up, with the correct height and atmospheric conditions. Indoor layout as well as home tightness matters. The issue is smoke roll in opening doors quickly. A lot can be done to minimize the issue.

Double wall chimney would be needed, possibly double wall connector pipe inside, which is close clearance pipe, for down to 6 inch clearance. This will prevent flue temperature cooling before entering chimney.

I would not go the expense of 8 inch new chimney and not have a chimney capable of connecting to a newer stove since most require 6.

I don't want to brag or anything, but here's my simple rendering. Does this help? Am I up a creek without a paddle?

 

[bholler]

I don't want to brag or anything, but here's my simple rendering. Does this help? Am I up a creek without a paddle?

View attachment 312743how far is the stove going to be from combustibles? How far will the pipe be from walls and the ceiling?

 

[ponto11]

You tell me. Flexible at this point. My understanding is the distances are determined by double wall v single wall. If double wall, I understand 6" and 8", respectively. @coaly said I need 18" for single wall.

 

[bholler]

You tell me. Flexible at this point. My understanding is the distances are determined by double wall v single wall. If double wall, I understand 6" and 8", respectively. @coaly said I need 18" for single wall.

Well the stove needs 36" inless you do an nfpa ventilated wall shield. Single wall needs 18". Double wall needs what is specified by the manufacturer

 

[ponto11]

Good to know. I'm flexible with the space. I need to understand if I can do this, and preferably with 6" double wall on the exterior.

 

[bholler]

Good to know. I'm flexible with the space. I need to understand if I can do this, and preferably with 6" double wall on the exterior.

I wouldn't use 6. Lots of people use it and get away with it. But I have also been called out on quite a few that didn't work. I think they work best on 7" honestly

 

[bholler]

But on the plus side a 6" chimney will be perfect for almost any modern stove when you replace that one

 

[ponto11]

But on the plus side a 6" chimney will be perfect for almost any modern stove when you replace that one

Yeah, I guess I don't want to do something not standard if there's a chance it won't work anyhow. And sounds like 6" not ideal.

 

[bholler]

Yeah, I guess I don't want to do something not standard if there's a chance it won't work anyhow. And sounds like 6" not ideal.

The downside is 8" will lock you into using an old inefficient stove or one of only 3 new ones that work with 8"

 

[ponto11]

The downside is 8" will lock you into using an old inefficient stove or one of only 3 new ones that work with 8"

Sounds like there are lots of down sides.

 

[bholler]

Sounds like there are lots of down sides.

Which is one of the main reasons using old stoves like these is getting less common