Chimney sizing for first gen Grandpa Bear stove

[Caddy Kid]

I recently purchased a Grandpa Bear square door stove for $50 in good shape for heating my barn this winter. This will be a new install, as the barn has not had a heat source in it before. It is a 1000 sqft barn with 16' ceilings and will have an inside pipe (one 90 off of the stove, up the wall to a 45, up the ceiling to another 45 into the double wall and out the roof)

I have never used this stove, and will be installing a new chimney pipe from the stove to the chimney cap. My preference is to use single walled pipe on the inside (for cost as well as radiant heat) and then of course a 4' section of double walled pipe out the roof.

I have been reading about adding a simple baffle, which sounds good, but it also seemed as though this stove has an oversized (8") pipe when its used as a wood stove (doors closed) and adding a baffle may well cool my pipe temps too much, and perhaps going with a 6" pipe would be preferential. Since that is not allowed per code, this is of course just hypothetical, but if one were to put a simple baffle in this stove (I burn kiln dried hem-fir cut offs from work) and keep the doors closed, then would it be advisable to use 6" pipe rather than 8" pipe as Fisher non-fireplace models of similar capacity did from the factory?

Hopefully this isn't stirring a hornets nest but before I go to the expense and effort I thought I would get additional perspectives. Thanks!

 

[Lake Girl]

Welcome to the forum! Wait until coaly shows up for a good answer as he is the "all things Fisher" guy

 

[Caddy Kid]

Thanks much! I live just a hundred or so miles from Springfield, and about 15 minutes from Redmond, so for me this is very much a "local" stove. Thanks!

 

[coaly]

The entire state of Oregon is EPA Certified appliances only. The law wasn't written for someone burning kiln dried fuel either...... That said;
You're right, it is technically against code to reduce pipe or flue size smaller than stove outlet. The stove was designed with the larger outlet for open door burning as well as connecting to larger existing chimneys or fireplaces. If code is not an issue, yes a 6 inch pipe and chimney is the way to go.
You're going to loose a lot of heat the chimney needs with that long run of single wall pipe. Lowering the front of baffle allows more heat up, so if you had double wall pipe inside you could make the opening the smoke rises through as small as the square inch area of chimney diameter. You may have to drop it a little to allow more heat up in the case of single wall pipe.
Here's a post (#28) burning similar dried cut offs, baffled correctly, complete with video;
https://www.hearth.com/talk/threads/cant-seem-to-figure-out.119184/page-2

 

[Caddy Kid]

Yup, thats (recent) Oregon for ya.

Now that I think about it, that baffle that you linked to seems like its pretty much exactly the configuration of the factory baffle in my Country or Lopi stove from a number of years ago. Good to know.

If one were to (hypothetically) install this older than EPA wood stove with a 6" pipe, where would it be best to place the 8" to 6" adapter? And about how much double wall pipe would be optimal? Thanks!

 

[coaly]

Reduce right at the stove.
Double wall would be best all the way.
You do get radiation off the single wall pipe, but the cooling gasses create a weaker draft slowing the fire. Now the stove doesn't come up to temp with a sluggish fire...... the hotter the burn zone the cleaner the fire. So it's best to loose less out of the stove, conserve heat all the way up and have a cleaner burning hotter stove.

 

[Caddy Kid]

Sounds great, thanks. I'll let you know how it hypothetically turns out!

 

[Caddy Kid]

Mine has the 20ga sheet metal bottom and back shielding on it and the non-ball feet legs, so I would guess its a late '77 to early '80?

Also, it looks like mine may have had the exhaust pipe replaced at some point. It has no shelf on the inside below the opening, and the whole thing is attached to the stove as a seperatly welded in square piece. So the round 8" pipe is welded into a larger square section, and then that whole thing is welded into the back of the stove. I would assume that was done at a later date?

 

[coaly]

Need pictures to determine what you have. Stove body with bent corners or angle iron, shields bolt on or welded, "Straight Leg" or angled outward "Fireplace Leg".

Yeah, that's not normal. The outlet hole could have been cut too large and saved the back piece with the patch. Fabricators tried to stock some thicker wall pipe with a larger outside diameter in the case of cutting too large. If it looks used hard, it could have developed stress cracks around the vent opening. They are normally stop drilled and welded without an issue.

 

[Caddy Kid]

Mine just has angle iron corners, welded on shield (but does have unused bolt holes in the shield metal, not the stove), and it looks like it used to have the straight adjustable legs, but someone cut off most of the bottom bit. It does have the double course of bricks up the sides. From what I can tell its not been run hard, no discoloration or anything and all but 2 or 3 of the bricks are unbroken. I do need to get a picture of the outlet hole though, just for curiosity sake.

 

[Caddy Kid]

I haven't made the baffle yet, but without a baffle and 16' of single wall 6" pipe, 2x 45 degree elbows, and 3' of double wall insulated chimney, its working like a charm.