To reduce stove pipe or not ?

[Todd_C]

I have a Grandpa Bear Fisher with a 8" back exit flue.
Looking at approximately 24ft of pipe to do the install.
Am I better off reducing the pipe to 6" for efficiency.
And is it ok to use a tee on the back instead of an elbow,
Then reduce the tee to 6".

 

[coaly]

A Tee on the back is fine since the downward leg allows condensate to drip down into cap without leaking out of a horizontal joint like an elbow connected on the back of the stove. Then the elbow needs to be inserted into the stove collar.

Depends on the Grandpa model.
If you have a Listed Series III or IV, it requires double wall inside for through the wall outdoor chimney.
Is this a later model with baffle or baffled older model?

Reducing depends on chimney and pipe configuration. Legally you can reduce by 1 inch in some locations, others no reduction is allowed. (where International Mechanical Code is adopted, but that doesn't allow the use of unlisted appliance at all) It will physically work with enough draft.

Describe the "24 feet of pipe". How much connector pipe, number of elbows, spark screen, (?) and how much chimney flue and what type?
These factors can cause smoke roll in when opening doors. A straight up installation with insulated pre-fab chimney is the best. I never heard of a problem with that configuration. You can even baffle it with a smoke space above baffle equivalent to the flue square inch area.

The use has to be considered when reducing as well. If you need the full heat capacity wide open, it is like running a restrictor plate on an engine reducing horsepower. If you're heat output is enough to bring it up to cruise and heat the area without pushing it, it's fine.

 

[Todd_C]

A Tee on the back is fine since the downward leg allows condensate to drip down into cap without leaking out of a horizontal joint like an elbow connected on the back of the stove. Then the elbow needs to be inserted into the stove collar.

Depends on the Grandpa model.
If you have a Listed Series III or IV, it requires double wall inside for through the wall outdoor chimney.
Is this a later model with baffle or baffled older model?

Reducing depends on chimney and pipe configuration. Legally you can reduce by 1 inch in some locations, others no reduction is allowed. (where International Mechanical Code is adopted, but that doesn't allow the use of unlisted appliance at all) It will physically work with enough draft.

Describe the "24 feet of pipe". How much connector pipe, number of elbows, spark screen, (?) and how much chimney flue and what type?
These factors can cause smoke roll in when opening doors. A straight up installation with insulated pre-fab chimney is the best. I never heard of a problem with that configuration. You can even baffle it with a smoke space above baffle equivalent to the flue square inch area.

The use has to be considered when reducing as well. If you need the full heat capacity wide open, it is like running a restrictor plate on an engine reducing horsepower. If you're heat output is enough to bring it up to cruise and heat the area without pushing it, it's fine.

76 with the 76 star.
The pipe goes out back to a 8" tee. Reduced to 6" at top of tee ?
Straight up thru ceiling to roof.I'm adding heat shielding to both side walls as a corner mounted system.

My thinking is that a 8" pipe will need more fuel to keep it hot than a 6" pipe will need. I'm hoping I can run it lower so we dontt bake ourselves out of the room
I don't plan on open door mode very often . But am concerned about not enough draft when doors are open. Don't want a smoke wagon.

 

[bholler]

76 with the 76 star.
The pipe goes out back to a 8" tee. Reduced to 6" at top of tee ?
Straight up thru ceiling to roof.I'm adding heat shielding to both side walls as a corner mounted system.

My thinking is that a 8" pipe will need more fuel to keep it hot than a 6" pipe will need. I'm hoping I can run it lower so we dontt bake ourselves out of the room
I don't plan on open door mode very often . But am concerned about not enough draft when doors are open. Don't want a smoke wagon.

Well i have found they work best on a 7" flue. I have seen lots of smoking issues with them running on 6". And these stoves will not run very low without making tons of smoke and creosote. Which is where stoves from this era including fishers got the name smoke dragon.

 

[Todd_C]

Well i have found they work best on a 7" flue. I have seen lots of smoking issues with them running on 6". And these stoves will not run very low without making tons of smoke and creosote. Which is where stoves from this era including fishers got the name smoke dragon.

I'm trying to figure out a way to keep the chimney hot while not baking myself out of the house. The Grandpa Bear is a big mamajama. But in the end it is what it is. I use a mama bear in my garage and it works fine. But will get the garage really hot if I bast away. My daughter uses a Grandma bear. hers can get really cookin when it's going. And tosses out tons of heat. But she has a open floor plan in her house.
I have a closed floor plan and am concerned about overheating the room it's in. With a 8 inch I have to keep it stoked to maintain chimney heat in the bigger pipe. Whereas with a smaller pipe I can maintain chimney heat with less stoking, once the fire box gets hot.
I appreciate your input on this!
BTW hers has a reduced pipe 6 inch . But has a top exit. The reducer seems to be factory installed and is not removable.

 

[bholler]

I'm trying to figure out a way to keep the chimney hot while not baking myself out of the house. The Grandpa Bear is a big mamajama. But in the end it is what it is. I use a mama bear in my garage and it works fine. But will get the garage really hot if I bast away. My daughter uses a Grandma bear. hers can get really cookin when it's going. And tosses out tons of heat. But she has a open floor plan in her house.
I have a closed floor plan and am concerned about overheating the room it's in. With a 8 inch I have to keep it stoked to maintain chimney heat in the bigger pipe. Whereas with a smaller pipe I can maintain chimney heat with less stoking, once the fire box gets hot.
I appreciate your input on this!
BTW hers has a reduced pipe 6 inch . But has a top exit. The reducer seems to be factory installed and is not removable.

Why not get a smaller stove or a modern stove that can be shut down better and still burn clean.

 

[Todd_C]

A Tee on the back is fine since the downward leg allows condensate to drip down into cap without leaking out of a horizontal joint like an elbow connected on the back of the stove. Then the elbow needs to be inserted into the stove collar.

Depends on the Grandpa model.
If you have a Listed Series III or IV, it requires double wall inside for through the wall outdoor chimney.
Is this a later model with baffle or baffled older model?

Reducing depends on chimney and pipe configuration. Legally you can reduce by 1 inch in some locations, others no reduction is allowed. (where International Mechanical Code is adopted, but that doesn't allow the use of unlisted appliance at all) It will physically work with enough draft.

Describe the "24 feet of pipe". How much connector pipe, number of elbows, spark screen, (?) and how much chimney flue and what type?
These factors can cause smoke roll in when opening doors. A straight up installation with insulated pre-fab chimney is the best. I never heard of a problem with that configuration. You can even baffle it with a smoke space above baffle equivalent to the flue square inch area.

The use has to be considered when reducing as well. If you need the full heat capacity wide open, it is like running a restrictor plate on an engine reducing horsepower. If you're heat output is enough to bring it up to cruise and heat the area without pushing it, it's fine.

I talked to my insurance agent and he said he was fine with the pipe reduction from 8" to 6". Along with proper heat shielding. Is your opinion that this reduction, mechanically speaking.will work? What are the pro's and con's to this installation?

 

[coaly]

Codes that adopt NFPA 211 Standard for solid fuel appliances allow 1 inch reduction. PA now under International Family of Codes uses International Mechanical Code which does not allow any reduction. (from stove collar size) International Code also requires all appliances to be UL listed.

That said, it is very common to reduce from 8 to 6. It depends on the chimney how well it will work. A straight up insulated metal fabricated chimney works fine. Masonry or horizontal runs can slow the draft that you could experience smoke roll in when opening doors. Depends on the chimney flue temp, exterior temp, and many other factors. The smaller diameter has less capacity. So wide open is not going to get as hot as 8 inch and also waste less. You don't run wide open much anyway, so cruise is normally fine with 6 inch.
The reason the Standard only allows 1 inch is to prevent the proper size pipe or flue from being restricted. In the case of Fisher double door stoves, they were oversize for open door burning and connecting to a larger existing flue in front of a fireplace. They would not allow enough heat up a larger flue if they were built with 6 inch. The cubic inch area of the firebox is about the same as a Papa which has 6 inch outlet, so expect it to physically work fine with a good drafting chimney. Many have baffled the stove as well when reducing so if adding a baffle, keep the smoke space exhaust travels over baffle plate the same square inch area of the flue. The more heat the chimney requires, the larger the smoke space. That can be adjusted by lowering the front of baffle for a larger space.

bholler has seen problems reducing more than 1 inch but they may be isolated cases with not enough draft or pipe configuration. He sees more chimneys than you or I hear about. No one here has told me they experienced any issue reducing to 6. I did it testing all models here with baffles on a 6 inch insulated Dura-Vent Chimney. (8 foot ceiling straight up into support box with 3 sections of 3 foot Chimney pipe)

Here is a thread with video of an Insert with added baffle reduced to 6. (Post #28) Insert was built with 8 to vent into existing fireplace flue that still didn't allow enough heat up flue to stay clean; And that was UL listed to be installed that way. I assume the new code requiring direct connection to liner supersedes the UL tested "safe way" in 1980 due to the test of time. Makes you wonder if any other UL safety tested practices we use today really aren't and could be deemed unsafe in later years....
https://www.hearth.com/talk/threads/cant-seem-to-figure-out.119184/page-2#post-1617042

 

[Todd_C]

Codes that adopt NFPA 211 Standard for solid fuel appliances allow 1 inch reduction. PA now under International Family of Codes uses International Mechanical Code which does not allow any reduction. (from stove collar size) International Code also requires all appliances to be UL listed.

That said, it is very common to reduce from 8 to 6. It depends on the chimney how well it will work. A straight up insulated metal fabricated chimney works fine. Masonry or horizontal runs can slow the draft that you could experience smoke roll in when opening doors. Depends on the chimney flue temp, exterior temp, and many other factors. The smaller diameter has less capacity. So wide open is not going to get as hot as 8 inch and also waste less. You don't run wide open much anyway, so cruise is normally fine with 6 inch.
The reason the Standard only allows 1 inch is to prevent the proper size pipe or flue from being restricted. In the case of Fisher double door stoves, they were oversize for open door burning and connecting to a larger existing flue in front of a fireplace. They would not allow enough heat up a larger flue if they were built with 6 inch. The cubic inch area of the firebox is about the same as a Papa which has 6 inch outlet, so expect it to physically work fine with a good drafting chimney. Many have baffled the stove as well when reducing so if adding a baffle, keep the smoke space exhaust travels over baffle plate the same square inch area of the flue. The more heat the chimney requires, the larger the smoke space. That can be adjusted by lowering the front of baffle for a larger space.

bholler has seen problems reducing more than 1 inch but they may be isolated cases with not enough draft or pipe configuration. He sees more chimneys than you or I hear about. No one here has told me they experienced any issue reducing to 6. I did it testing all models here with baffles on a 6 inch insulated Dura-Vent Chimney. (8 foot ceiling straight up into support box with 3 sections of 3 foot Chimney pipe)

Here is a thread with video of an Insert with added baffle reduced to 6. (Post #28) Insert was built with 8 to vent into existing fireplace flue that still didn't allow enough heat up flue to stay clean; And that was UL listed to be installed that way. I assume the new code requiring direct connection to liner supersedes the UL tested "safe way" in 1980 due to the test of time. Makes you wonder if any other UL safety tested practices we use today really aren't and could be deemed unsafe in later years....
https://www.hearth.com/talk/threads/cant-seem-to-figure-out.119184/page-2#post-1617042

Thank You.
I have been reading threads all day to make sure I wasn't barking up the wrong tree on this, buying 6" pipe only to have to go bigger later.
What I have read so far backs up what you just posted.
My primary use of the Grandpa bear is for heating not necessarily fireplace mode.
I've had enough with the shysters who sell propane in my neck of the woods.
Besides having the ability to heat any way I choose, gives me more diversity.


Where the double doors meet, Is there a small gap on the inside edge of the top and bottom all these doors. Right on the top and bottom of the seam.
Also on the 76 double door can I expect there to be nickle plating on the letters, art work or 4 fin baffles if I strip them.

 

[coaly]

The round door seal type will have small leaks top and bottom at door seam.
The doors were originally painted black.
Nickel and brass plate wasn't available until 1980 on the Cathedral doors.

 

[Todd_C]

Check this one out. They say Grandma Bear with glass doors.
(broken link removed to https://minneapolis.craigslist.org/wsh/for/d/fisher-wood-stove-grandma/6487057597.html)

 

[coaly]

Yes, that is a Grandma IV with Fireplace Legs.