Decided to keep the grandpa bear

mm1988

New Member
Nov 23, 2020
5
NWGA
Hello, I am new to this forum but not to wood heating. I’ve been heating my home with a grandpa bear rear vent fireplace series for three years. This year I was considering replacing the fisher with a Vermont castings or Woodstock to conserve wood. Due to the placement of the flue being located 24” off floor on the rear I’m limited as to options to replace the fisher.

I’ve decided to keep the fisher and buy a wood splitter. You can’t beat the capacity and heat output/duration of this stove. I have 8 acres to cut on and the stove is a piece of history. I wanted to show off my stove and see if any others have struggled with replacing an old love.

If anyone knows where I can purchase a pre cut baffle for this stove please let me know.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,053
NE PA
Shipping would be more than cutting a baffle plate. You would have to give anyone measurements since they can be different width, and front to back is made for your venting square inch area.

Whatever your pipe and flue diameter is, figure square inch of diameter. (Example, square flue 8X8 is 64 ; round is calculated square inch of circle size) This is the minimum square inch opening you need that the exhaust travels through above baffle plate. (From front plate edge to lower bend in top) Make a cardboard template to measure this square inch area as it will sit on support bricks. 1/4 inch or so smaller than width across is fine to install and for expansion. Take that template to any welding shop and ask for 5/16 thick mild steel that size. Some order precut, so there is a small cut charge. You can then lower plate if needed to enlarge the opening area as needed for pipe configuration in case your system has too much resistance. (Elbows, or horizontal pipe runs, or extreme height) In most cases the minimum square inch area is fine.

I weld or bolt a short piece of angle iron to each end of baffle to hold bricks upright against stove sides.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,053
NE PA
For duration, loading and fuel consumption a Papa with insulated 6 inch flue beats any Fireplace Series. Log length is longer, so less cutting, and the way air goes between split logs in the stove lengthwise ignites far better than across. They literally sound like an oil burner when you open the air for quick ignition. You end up with much more top surface and the stove is simply built to the shape of firewood being deep and narrow. Baffle is the same design, much smaller so 1/4 inch is acceptable being half the width. Hearth size could be a factor, and setting them across the hearth is what they were designed for with a side vent.
 

Frankdozer

Member
Aug 31, 2016
97
Maine
This past winter, pre pandemic, I perused EBay for a plate for my Grandma Bear. I ordered a 5/16” X 9” X 22.75” mild steel plate for $18.75 shipped. I just now tried to find that seller for you to contact but to no avail. The plate fit as hoped it would.
 

mm1988

New Member
Nov 23, 2020
5
NWGA
For duration, loading and fuel consumption a Papa with insulated 6 inch flue beats any Fireplace Series. Log length is longer, so less cutting, and the way air goes between split logs in the stove lengthwise ignites far better than across. They literally sound like an oil burner when you open the air for quick ignition. You end up with much more top surface and the stove is simply built to the shape of firewood being deep and narrow. Baffle is the same design, much smaller so 1/4 inch is acceptable being half the width. Hearth size could be a factor, and setting them across the hearth is what they were designed for with a side vent.
I actually considered buying a different fisher. I think I’m better off keeping this one as it would be difficult to get another if I decide I don’t like the EPA stove. As you know If you use the draft controls properly on this model it actually burns very efficient, which I didn’t when I started using it. I love the stove and see no reason to go with a epa, also I’m lazy and don’t have to split the wood as small.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
23,118
central pa
Mine has an 8inch rear outlet reduced to 6in to catch the steel 6in chimney. I live in GA so I’ve only had to use it 6 times this year 2-2.5 cords of hardwood gets me through the coldest of winters. I’m attaching the pics I forgot to attach thanks for the help everyone
How close is it to that stone and what is behind the stone?
 
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mm1988

New Member
Nov 23, 2020
5
NWGA
How close is it to that stone and what is behind the stone?
It’s 10in off the back of the hearth and it’s fireproof board and then the chimney extends directly behind it. It’s not necessarily ideal but the hearth was custom built to the stove I had it inspected when we bought the house.

Does 9in wide and 24in long L to R sound about right for a baffle?
 
Last edited:

bholler

Chimney sweep
Staff member
Jan 14, 2014
23,118
central pa
It’s 10in off the back of the hearth and it’s fireproof board and then the chimney extends directly behind it. It’s not necessarily ideal but the hearth was custom built to the stove I had it inspected when we bought the house.

Does 9in wide and 24in long sound about right for a baffle?
But is that board on wood framing?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
23,118
central pa
Not directly behind it’s boxed out with a chimney behind it I believe. When I had the house inspected they also checked the chimney and stove.
But it is just a prefab chimney right? What is on the outside of the house there? If this is done wrong it can be extremely dangerous. That stone and probably cement board transfers heat very well and if that is directly on framing 10" is way to close. If it is a ventilated heat sheild that 10" would probably be fine because the clearance is to the framing behind which would be 12" with a proper sheild. Without proper ventilation you need 36"
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,053
NE PA
Time to find a new inspector. The heat shield criteria in NFPA 211 has been around a long time.
The measurement goes from stove to combustible wall, not the heat shield, so it could be 12 inches.
As long as the cement board is 1 inch off the wall with an open air space below for air intake to allow heated air to rise out behind it, and open at top you're ok. That would be an approved heat shield. Anything less is not a heat shield. It can't be in direct contact with wall. (and no 1" ceramic spacer in the centerline of stove behind it) Solid brick in direct contact allows 33% reduction from 36 inches without shield. That would be down to 24 inches. With air space, 66% clearance reduction is allowed down to 12 inch clearance to wall.

That sounds small for the baffle.
6 inch pipe is 28.26 square inches.
24 wide would be an opening about 1 1/4 inch between plate and top for a 30 square inch smoke space for exhaust to travel. So you need to make the cardboard template and set it in place like you would the baffle plate. Angle it upward at front toward lower bend in top. It can go forward of the bend if you don't burn with open doors with a screen in place. That will give you the plate measurement. If you cut a 2 x 3 notch out of each front corner, you have the same design that was tested in the later models. It wasn't as large since they were designed to use a larger existing chimney flue from a fireplace, so they had to allow more heat than necessary up the chimney not knowing what size chimney would be used. You can fine tune for your vent system for the best efficiency. Lowering the font slightly increases the vent space in case you need more heat left up. 1 1/4 is a good starting point for straight up insulated flue pipe. If you look at baffle design in newer stoves, you'll find they cover the firebox even farther forward. As long as there is no smoke roll in issues when opening doors, use the minimum square inch area to match chimney.

Here is a factory baffle with large smoke space. The notches prevent stagnation in corners. This is the condition of baffle after burning over 25 years without cleaning. 5/16 stays flat with no wear or rust evident. Pictured as used.
Smoke Shelf Baffle 1984 Goldilocks.JPG
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
23,118
central pa
What does it mean : The notches prevent stagnation in corners?
It helps minimize the area of dead air you would typically get in the corners
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
23,118
central pa
Time to find a new inspector. The heat shield criteria in NFPA 211 has been around a long time.
The measurement goes from stove to combustible wall, not the heat shield, so it could be 12 inches.
As long as the cement board is 1 inch off the wall with an open air space below for air intake to allow heated air to rise out behind it, and open at top you're ok. That would be an approved heat shield. Anything less is not a heat shield. It can't be in direct contact with wall. (and no 1" ceramic spacer in the centerline of stove behind it) Solid brick in direct contact allows 33% reduction from 36 inches without shield. That would be down to 24 inches. With air space, 66% clearance reduction is allowed down to 12 inch clearance to wall.

That sounds small for the baffle.
6 inch pipe is 28.26 square inches.
24 wide would be an opening about 1 1/4 inch between plate and top for a 30 square inch smoke space for exhaust to travel. So you need to make the cardboard template and set it in place like you would the baffle plate. Angle it upward at front toward lower bend in top. It can go forward of the bend if you don't burn with open doors with a screen in place. That will give you the plate measurement. If you cut a 2 x 3 notch out of each front corner, you have the same design that was tested in the later models. It wasn't as large since they were designed to use a larger existing chimney flue from a fireplace, so they had to allow more heat than necessary up the chimney not knowing what size chimney would be used. You can fine tune for your vent system for the best efficiency. Lowering the font slightly increases the vent space in case you need more heat left up. 1 1/4 is a good starting point for straight up insulated flue pipe. If you look at baffle design in newer stoves, you'll find they cover the firebox even farther forward. As long as there is no smoke roll in issues when opening doors, use the minimum square inch area to match chimney.

Here is a factory baffle with large smoke space. The notches prevent stagnation in corners. This is the condition of baffle after burning over 25 years without cleaning. 5/16 stays flat with no wear or rust evident. Pictured as used.
View attachment 267648
Has that baffle really been used for full time heat for 25 years? If do I am very impressed I have never seen one that flat.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,053
NE PA
Yes. I bought it new and it was my only heat source until I added onto the house. I even took it out and laid it flat and flipped it over to see if it rocked. Lays flat! 5/16 thick, same as top. Everything on the stove is straight.
 

Frankdozer

Member
Aug 31, 2016
97
Maine
It helps minimize the area of dead air you would typically get in the corners
How do I know about the dead air in the corners? What led you to think “ I need to notch the corners”. I did not notch mine but for a specific reason it is easily done and I would do it.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
23,118
central pa
How do I know about the dead air in the corners? What led you to think “ I need to notch the corners”. I did not notch mine but for a specific reason it is easily done and I would do it.
I don't think it is nessecary and I would think it would accelerate warping. But it clearly hasn't in coalys so I don't know. But there is still plenty of creosote buildup in the corners on his stove. Maybe not quite as much as others I have seen but not that much difference.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,053
NE PA
Coaly.. would you still recommend the same size 2X3 notches on a baffle plate for a baby bear?
No. The deeper single door stoves do not come near as close to the stove front.

I suppose if you made an oversized baffle closer to the door it would be advantageous to get more heat into the front corners. Baby Bear with a smaller firebox infringes on space, so I keep the baffle to the rear angled towards the lower bend in top to prevent infringing on loading capacity.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,053
NE PA
How do I know about the dead air in the corners? What led you to think “ I need to notch the corners”. I did not notch mine but for a specific reason it is easily done and I would do it.
The notches were designed by Fisher research and development team.

The Smoke Shelf Baffle was tested to decrease smoke particulate from 60 g for every kg burned down to 6 g for every kg burned. The stricter EPA regs it was done for required smaller particular that they could not achieve. You will notice a drastic reduction of smoke when starting the stove with baffle installed.

If you use an IR thermometer on each square inch of the stove top you will see the temperature difference. The front corners get little movement since the heat “pours” over the baffle plate towards the flue vent.

To visualize how hot gasses flow it is like hot air rising in a home. Picture the home or firebox turned upside down. The heat source is like a water faucet coming from the logs. It hits the bottom of baffle and pours over the edge. (Any remaining unburned particles that contact the hot baffle burst into flame as sparks as long as there is sufficient oxygen above the fire). Upside down, the flue vent is like a drain. The water pours over baffle, some directly down the drain, some pouring onto the stove top which fills the top area until deep enough to go down the drain which is sticking up 3 inches on a top vent. This water quickly makes it’s way toward the drain. The notches allow more water to flow into the corners, along with turbulence. This prevents cooler front corners. Same with a rear vent. The flow of heat is toward the rear, so you need more spilled at the front corners to heat there evenly.

The temperature of baffle plate becomes an ignition source like a spark plug to ignite smoke particles. That is why plate thickness and material was chosen to be steel and the thinnest to retain heat, yet thick for longevity. The thicker the metal the more mass. This moves heat away faster, so a huge 1 inch plate that would last forever has more capacity to move heat and stay cooler. Like a colder spark plug. So I use 1/4 plate in narrow stoves where warpage and sag is not as much a factor. 5/16 runs cooler but is needed in wider stoves.

I tested many size and thickness, angles and designs including a saw tooth edge that has less ability to cool itself. (less material at points to move heat away) This is why you don’t want cast iron due to moving heat away rapidly. The fabrication without a laser cutter wasn’t worth it. I also made a hollow baffle with holes in the bottom for secondary air. Had that been known back in the early 80’s Fisher could have easily passed the 1988 regs and continued in business. I tried it and worked fine. I never have premium dry wood, so burning standing dead and storm damaged stuff that doesn’t sit a year or more wasn’t good for me. With an RV business during summer and heating business during winter, I never had time to split stack and store as I should in advance. Retired from both businesses, a few years I was able to get ahead. Then I started maintaining a large Chinese restaurant while remodeling homes to rent. So much for retirement. I burn coal half the time since it takes no time to process and burns while I’m not home. I lost secondary flame due to too much vapor carrying heat away and realized secondary combustion wasn’t for me.