Baffle question on a Grandpa bear

[Jeffersontim]

I recently purchased a house with a ~79 Grandpa bear woodstove in the basement connected to a masonry chimney exterior to the home. I spent some time and re-bricked the interior of the stove as most of the bricks were deteriorated, the outside of the stove is in good shape. I also installed a baffle sitting on bricks. I fired it for the first time last night on seasoned wood that was dry and got a ton of heat off the unit but ran a cold stack, relatively speaking. The temps that I was averaging on the burn was ~500 - 600 on the top of the stove and ~250 on the pipe where it meets the brick. I know that I need to get the stack temps higher then 250 to prevent creosote, what I don't know is how to do that without turning my house into a sauna. The baffle is angled and the highest point is 2" below the low part of the top, if I drop the baffle down decreasing the angle will that increase the heat going up the stack? Any tips or advice is appreciated as I am brand new to the heating with a stove game. The house is ~1600 sf rancher on a full basement and the basement is set up with vent fans that pull the heat up to the main floor with an open stairwell for a return.

 

[coaly]

Welcome to the Forum !
I assume pipe damper is wide open if you have one. Outside of pipe temperature isn't near as hot as flue gasses, so it's only an estimate without a probe inside pipe.
Yes, dropping the baffle at front for a larger smoke space allows more heat up stack. Other factors are how many elbows, length of pipe, chimney cap and screen...... This all reduces draft requiring more loss up stack.
You can see why a 6 inch stove (or yours reduced with liner) works so much better with much less heat wasted to keep that big flue hot.
Running half the stove temp where pipe enters chimney (600 stove top - 300 pipe) is great with insulated flue that has minimal heat loss. Is your chimney indoors or out?

If you can get "The Woodburners Encyclopedia" by Jay Shelton off eBay, you'll find a wealth of information for the price. I have most of the books recommended for further reading in the Fisher manuals, and that one has the most info and explains technical terms, even stove progress through the years.

 

[Jeffersontim]

Welcome to the Forum !
I assume pipe damper is wide open if you have one. Outside of pipe temperature isn't near as hot as flue gasses, so it's only an estimate without a probe inside pipe.
Yes, dropping the baffle at front for a larger smoke space allows more heat up stack. Other factors are how many elbows, length of pipe, chimney cap and screen...... This all reduces draft requiring more loss up stack.
You can see why a 6 inch stove (or yours reduced with liner) works so much better with much less heat wasted to keep that big flue hot.
Running half the stove temp where pipe enters chimney (600 stove top - 300 pipe) is great with insulated flue that has minimal heat loss. Is your chimney indoors or out?

If you can get "The Woodburners Encyclopedia" by Jay Shelton off eBay, you'll find a wealth of information for the price. I have most of the books recommended for further reading in the Fisher manuals, and that one has the most info and explains technical terms, even stove progress through the years.

Coaly, thank you for you response. I did install a damper in the pipe and it is wide open, figured better to have and not need then need and not have. The chimney is outside and unlined. The stove is a rear exit and has 2 elbows with 30" of single wall to get to the masonry chimney. The chimney was purpose built for the stove back in the day and it does have a cap with a screen. We did have the chimney inspected and was told that it is in good shape and clean inside. I think somewhere along the line I will get the chimney lined and reduce to 6" but for now I am running with the 8" and it is a beast. I will check out the books that you recommended. The thermometer that I have on the pipe is at the base of the second elbow right before it enters the masonry. The colder the stack got the thicker the smoke got, now I know why they call them smoke dragons.

 

[coaly]

You should not be getting that much smoke with baffle plate. A little at start up, and it should clear up as it comes up to temp.
When starting, the air intakes should be a couple turns open. As the kindling roars, close damper until roar stops. This will allow it to have as much air as it needs, yet slow fire and prevent all the heat from escaping. This heats the larger wood to get it started, it is not the time to close air intakes to control fire by depriving it of oxygen. Open damper each time you open doors. As it catches, slowly close air intakes instead of closing damper. About a turn and a half should get it going. Then when up to temp, about 1 turn each open or less for desired heat output. Keep air space between logs, they should be split. If you see smoke, give it air.

If it doesn't work as described above, maybe you should try without baffle in case the plate isn't right.
Pictures of baffle plate with doors open may help. The plate should be angled upward toward the lower bend on the top, and smoke space (area exhaust travels) should be measured between baffle plate edge and top radius bend.

 

[Jeffersontim]

Thank you for the step by step, I will try it tonight when I fire it again. I will also try and remember to snap a picture. The plate is 26.5 inches across and 13 inches deep and is sitting on the shelf at the exhaust port. The front of the plate is propped up on 2 Fire bricks sitting on the brick retainers. I spotted it down once I got home to give me 3 inches of space between the bottom of the bend of the top plate and the forward edge of the baffle. I am thinking that I was starving the fire of air to much and did not really get it to a steady state last night. I will post the results of tonight's burn tomorrow. Thank you again for the step by step as I know nothing about wood stoves except what I have read on here.

 

[coaly]

Not a problem.
Sounds like it didn't have enough air to me too.
If you hear any sizzle or see any liquid bubble from log ends, your wood is not dry enough. That will cause slow ignition and all sorts of problems. That book goes into detail about the BTU needed and what water vapor does as it exits a log. You'll have a far better understanding of the gas you're burning from wood (the flame) and what affects it with that book.

I have a neighbor across the street from my log cabin that bought a new Lopi last year, complete with chimney and inside air intake. I can start my Baby Bear across the street at the same time and have a clean stack sooner than his. Once mine is up to temp, I can feed it slowly keeping it far hotter constantly than his "clean" burn cycles. When his burns down to coals, his house cools, and a new load put on when the coal pile permits starts the smoke until the secondaries are lit again. He's back to a smokey start until up to temp while mine is a constant light haze that doesn't drift much farther than my roof edge. I just don't see why they were termed smoke dragons unless burned incorrectly. ANY stove or open fire can be burned that way if you try. By the end of last winter he was disgusted with his heat output. I tried his through a burn cycle and assume we were doing right. He has a moisture meter I suggested and has premium dry fuel. (far better than mine) About 2 hours of clean secondary burn was it, then coals until it was burned down enough to reload. I need to be able to load and do something for 5 or 6 hours and come back to a warm house. He's adding electric baseboard as an alternate this year. I don't have electric at my cabin, and I use mine for the only cook stove as well. His won't boil water. It's strictly a space heater. His is installed in a corner since it has reduced clearance down to a few inches. Mine is in the center where it belongs and radiates in all directions. He even had a freeze up under his sink last year....... hence some added electron flow .
Our "cabins" are identical 3 bed room log home kits brought from Finland under 1000 s.f.

 

[Jeffersontim]

I am not a fan of the newer stoves, way to fragile looking and picky. I want a stove that I can mess with and if like last night don't get it right I am not going to mess it up. I was impressed that it was still warm when I got home from work 19 goes later and there was still some coals in the bottom. I had to let it go all the way or to be able to mess with the baffle a bit. With any luck I will get it right tonight, thank you for your help you have a wealth of fisher and woodstove knowledge. I am happy overall with my grandpa bear.

 

[Jeffersontim]

Here is my current set up. I ran the other night and I was getting somewhere but then the winds kicked up to 25 and that made it hard to dial in. I am going to keep playing with it and see what I can do. Lowering the baffle plate down helped somewhat but my stack tempos are still a bit low. I am looking into getting a prove style thermometer and I might try pulling the baffle or all together to see what I can get. I want to try another burn where things are when the winds are not kicked up so high.

 

[coaly]

Your baffle should be lower in the back. Try setting it on the rear brick retainers with the same opening at top. That should give you about a 30 degree angle. (Keyword in my post #4 above "The plate should be angled upward" ) Your flat plate absorbs more heat from flame tips as well cooling the burn zone. This is more flame impingement than necessary.
Cut corner notches in the baffle plate 3 inches in from sides, and 2 inches in from front as shown below. This will prevent stagnant flow in front corners for more even surface temperature.
Wind will have a slight effect on draft, but not much unless it is associated with a low pressure area.



This will give you higher flue temperatures, strengthening draft to overcome wind and other detrimental factors.

 

[Jeffersontim]

I will try dropping it down to the retainers tonight and fire again. I take it the 30 degree angle helps with the flow inside the stove. How hot is too hot for the stove top and the stack? I will cut the corners out as soon as I get all my tools unpacked but that might be a bit, is that a critical thing or can it wait.

 

[Jeffersontim]

The last time that I fired the stove I ended up with 700 stove top and just under 300 on the pipe.

 

[coaly]

You should be able to close air intakes for a 600 to 650 stove top and have more like 350 on the pipe. I think you'll find tilting the baffle is all it needs.

It also allows faster flow. That means faster through the intakes as well. You want a smaller intake area with faster moving air. This mixes with the gasses escaping from wood for a cleaner burn with better oxygen mix. If you slow it down with flat baffle or pipe damper, opening the air intakes more allows the correct amount of air, but at a slower velocity. You want turbulence for a better mix.

Corners are not critical, but helps keep the corners as hot as the rest of the top.
Keep it below 800. Intermittent high temps won't do damage. Paint will discolor to gray or white.

 

[Jeffersontim]

Once you said tilt the baffle more I figured the air velocity was to slow. Now looking back at the temp difference I suspect you are right and I did not have the air moving fast enough to get the heat pulled up the stack.

 

[coaly]

Yep, plus the hotter the flue, the lower the pressure in stove, so the atmospheric pressure at any given time has a greater pressure difference to push into the stove. Your test fires are just getting the flue up to temp and going out. It will act different with 24/7 burning and colder temperatures.
Then you can fine tune the angle by sliding bricks forward and back to raise and lower plate. Lining flue with an insulated liner allows even farther closing. So it pays for itself with less wood usage and less cleaning over time.

You can bolt or weld angle iron on the plate to prevent bricks from falling inward as shown below;


"Too hot" for the stack is any wasted heat over 250* at the top. Theoretically that would be optimum temperature to achieve. You're not doing that without a barometric damper that constantly self adjusts to keep draft and flow through firebox precise. They are used on coal stoves for precise flow through fire bed that is more critical than wood. They should not be used on wood stoves that create creosote in case of chimney fire. It would open to slow draft by allowing cooler indoor air into chimney, feeding the chimney fire.

 

[Jeffersontim]

I will see what happens tonight. When I pull the plate to cut the corners I think I will weld on some angle to hold bricks in place as I would not want to have to t try and reset a fallen brick mid burn. I look forward to consistently cooler tempos to be able to run the stove 24/7 but right now it is throwing of more then enough heat in s few hours to keep house warm till following evening. I know I am not doing myself any favors with these little fires as nothing in the stack is actually getting up to any kind of temp before the fire goes out. Looking ahead at the forecast the tempos are tending down so here is hoping. Thank you for your advice and I will post an update tomorrow.

 

[Jeffersontim]

I dropped the back of the baffle down to the retainers and moved the leading edge up towards the bottom bend of the top plate. The gap is 2 inches and we are still closer but not there yet, I will try dropping the front back down to 3 inches and see what that gets me tomorrow night.

 

[coaly]

That's what I like about the angle iron on the baffle. I adjust the bricks fore and aft with it going with a poker with no fear of them falling.

Another trick is using a long log or board a little wider than stove width inside. Wedge it between bricks across stove to hold them in place. Set baffle on bricks and slide back until it drops in the rear onto shelf. Then remove wedged in cross brace. I've done it full of coals with welder gloves in a Mama. Papa is deep and I wouldn't try that one hot.

 

[Jeffersontim]

Yeah I have got to get those weeks on sooner rather then later so I can adjust on the fly.

 

[Jeffersontim]

Dropped it back down to a 3 inch gap and we seem to be happy somewhat. I also need to get some seasoned oak to try. I forgot that I have mulberry mixed in with my maple and it burns hot. I remembered it was in there when I smelled the smoke and it had a sweet smell to it. I hope to have the oak the week after thanksgiving and then do all this over again. I will guess the oak will help me or with stake burn Temps.

 

[RMJ1216]

Hello,

I just recently restored a Grand Pa Bearwith Grand Ma Bear doors. I would like to install a baffle what should the depth of the baffle be (front to back)

Thanks
Rick

 

[coaly]

You're not fabricating the baffle for the stove, you adjust angle and size for the chimney.

Depends on the chimney flue diameter, height, and pipe configuration. The more heat you need to leave up to maintain 250* at the top, the smaller the baffle to allow more heat up.

Start with a cardboard template sitting on the rear brick retainers and angle upwards at the front towards the lower bend in the top.
8 inch flue = 50 1/4 square inch opening minimum (smoke space). Increase this opening size when more heat is required up chimney. (same square inch area as chimney flue diameter if larger)

 

[RMJ1216]

I plan on using a double wall 8” chimney that is roughly 13’ tall from stove to cap. I have read about reducing the chimney to 6”, is this ok or should I stick with the 8”. I read the the stove is more efficient with the baffle plate and want to set it up correctly. Thanks for your help with this. I attached a photo of my Grandpa Bear with Grandma Bear doors, almost done with the restoration.

 

[RMJ1216]

Here’s a picture with the cardboard template. The cardboard is 26.5” wide and 12” front to back.

 

[Todd67]

There is some great info in this thread!

 

[RMJ1216]

Thanks! Lots of good info here.