Changing the flame path on my fisher stove

After reading a bunch of posts on Old fisher stove baffle plate

This is essentially what i used to have for a baffle


It worked ok. however smoke was still a serious part of the stove. And quite alot of the wood would burn up quickly. It took me about 40 minutes in the morning to get one liter of water boiled. Also i really had to gun the stove to get a hot fire. It heated well. Though it lost that heat just as quick.

I have since thanks to many threads on permies. Changed my baffle plate around and added a new one. See photo

Note not my stove.


I now have a better performing stove thanks to this simple addition. It heats up easier. it holds the heat for longer. It Smokes less. and as far as i can tell it uses less wood.

I have about three inches of clearance to the front door and three or so inches of clearance to the top of the stove.


This worked for about 1 day until i discovered i had many air leaks. The flame path was going about 4 different directions.

so i was not completely satisfied with the improvement. The old bricks i had cobbled together were slightly different heights. And they had more joints which meant more air gaps. The flame path was going every way.


I am not super stoked about these bricks. They are about 1000 grams lighter than the other brick i have




Than i decided to put myself in my firewood's position!


3 new bricks on each side and 3 smaller pieces for the back of the stove.


Now the flame path is pulling up to the front of the stove. Much better!


Top of stove with our hot water heater in the stove pipe.



I am soon to be getting a Infrared Gun!

So i will be able to get some temps on the stove.

To see the original post on Permies
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,180
NE PA
If you look at baffles in the new stoves, you’re very close to their design. I angled the baffle to increase velocity and heat going up chimney. This angle is important for two reasons. The steeper the angle, the faster the exhaust rises up it, increasing velocity up stack. This is required in some installations where connector pipe configuration causes resistance, or oversize chimney flues that require more heat and velocity to increase net draft. The baffle angle and size depends on the chimney, not the stove. Whatever your square inch diameter of flue is, you can raise your plate so the square inch area the exhaust travels through is the same square inch opening as flue.

The second reason for an angled plate is flame impingement. Allowing the flame tips to come into contact with plate instead of rising up it removes too much heat from the tips lowering the burn zone temp. It chills the flame tips. Carbon deposits on the baffle is a sign of absorbing flame tip heat lowering the combustion temp. As long as you get no deposit on baffle, you’re hot enough. By the looks of your fire and outdoor temps you’re probably ok. That may not work well for someone in Virginia where outdoor temps are moderate and they burn much smaller fires.

You’ll be amazed at the temperature difference on different parts of the stove. The main use of the IR gun is checking pipe temperature above your water heater that removes a ton of heat from the chimney. Check the surface temp of the pipe where it enters chimney. The surface temp will be about half the actual flue gas temperature. Then guess the temperature drop all the way to the top. With the IR thermometer you can check flue temp near the top. About a foot down on the inner flue sidewall it needs to be 250*f. or above. This is when smoke is present. Below that is creosote forming, above that is waste going up the chimney. Then you will know what you need inside on the pipe to achieve the desired temp at the top. I’m assuming removing so much heat with the water heater you have a 6 inch diameter flue and hopefully insulated to stay hot enough all the way up. Amazingly a 6 inch pipe allowed to expand into an 8 inch flue drops by about 1/2 the temp! You’ll find many more uses for the IR thermometer. If you check other installations for safety and clearance issues, check surface temp of combustible materials where in question with it. 115*f. over ambient air temp is where pyrolysis takes place and you know more clearance or shielding is needed.
Your pic seems to have some serious clearance issues.
 
If you look at baffles in the new stoves, you’re very close to their design. I angled the baffle to increase velocity and heat going up chimney. This angle is important for two reasons. The steeper the angle, the faster the exhaust rises up it, increasing velocity up stack. This is required in some installations where connector pipe configuration causes resistance, or oversize chimney flues that require more heat and velocity to increase net draft. The baffle angle and size depends on the chimney, not the stove. Whatever your square inch diameter of flue is, you can raise your plate so the square inch area the exhaust travels through is the same square inch opening as flue.
So i am relatively new to fisher stoves. I have had this for 4 winters now. Are you meaning to say that there are new "fisher stoves"? From my readings. I have a 6 inch pipe with a square inch diameter of about 30. The thing is. This stove rips air. I can hear it from 15 feet away. As far as i can tell i have more draft than i need.

The second reason for an angled plate is flame impingement. Allowing the flame tips to come into contact with plate instead of rising up it removes too much heat from the tips lowering the burn zone temp. It chills the flame tips. Carbon deposits on the baffle is a sign of absorbing flame tip heat lowering the combustion temp. As long as you get no deposit on baffle, you’re hot enough. By the looks of your fire and outdoor temps you’re probably ok. That may not work well for someone in Virginia where outdoor temps are moderate and they burn much smaller fires.
I am not quite sure i understand the flame tip part. Nor the burn zone temp. Care to elaborate? I have been noticing how much hotter the stove runs, while at the same time i appear to be using less wood. Right now i can place the wood at the back of the stove and it becomes cherry hot in there. I have also noticed less smoke, however i do not inspect how much is coming out all of the time. The firebricks turn red/glowing. I am quite sure it is getting hot in there. If anything i have increased the temp inside the stove. At least that is what it looks like from my point of view.

You’ll be amazed at the temperature difference on different parts of the stove. The main use of the IR gun is checking pipe temperature above your water heater that removes a ton of heat from the chimney. Check the surface temp of the pipe where it enters chimney. The surface temp will be about half the actual flue gas temperature. Then guess the temperature drop all the way to the top. With the IR thermometer you can check flue temp near the top. About a foot down on the inner flue sidewall it needs to be 250*f. or above. This is when smoke is present. Below that is creosote forming, above that is waste going up the chimney. Then you will know what you need inside on the pipe to achieve the desired temp at the top. I’m assuming removing so much heat with the water heater you have a 6 inch diameter flue and hopefully insulated to stay hot enough all the way up. Amazingly a 6 inch pipe allowed to expand into an 8 inch flue drops by about 1/2 the temp! You’ll find many more uses for the IR thermometer. If you check other installations for safety and clearance issues, check surface temp of combustible materials where in question with it. 115*f. over ambient air temp is where pyrolysis takes place and you know more clearance or shielding is needed.
Your pic seems to have some serious clearance issues.
Thank you for the nudge on the clearance issue. It has been on the list for a few years now. We have the material. however the ir gun will help show us what is needed.

Yes the ir gun will be quite handy to have. So our chimney is all straight. It goes i would say 20 feet in the air. It is double walled insulated pipe starting 6 feet above the stove. If i counted correctly about 5 pieces which are 3 feet long. So about 15' of it is double walled insulated.

I hope to post photos of the IR gun results.
 

coaly

Fisher Moderator
Staff member
Dec 22, 2007
4,180
NE PA
No newer Fisher stoves since 1988 in North America. Only New Zealand and Australia.

Your draft can probably use a flue damper to slow it until the roar stops. Your flames are sideways, not hitting the plate on a 90* angle to cause a loss of heat from flame contact.

Do you use any thermometer on the pipe for an idea of flue gas temp? Without that, your guessing and probably still wasting heat up the chimney even with the larger baffle. Slowing the rising gasses with a damper decreases draft slowing the incoming air. The flue damper is a chimney control that slows an over drafting chimney that affects the stove.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
23,996
central pa
No newer Fisher stoves since 1988 in North America. Only New Zealand and Australia.

Your draft can probably use a flue damper to slow it until the roar stops. Your flames are sideways, not hitting the plate on a 90* angle to cause a loss of heat from flame contact.

Do you use any thermometer on the pipe for an idea of flue gas temp? Without that, your guessing and probably still wasting heat up the chimney even with the larger baffle. Slowing the rising gasses with a damper decreases draft slowing the incoming air. The flue damper is a chimney control that slows an over drafting chimney that affects the stove.
Don't forget he has a water heater rigged in the stove pipe. So there will need to be a fair amount of extra heat going up the stack to counter that loss.
 

Jeremy B.

New Member
Dec 8, 2020
2
northern vermont
when you added the larger baffle plate does it limit how much wood you can put in the stove overnight? i got my first papa bear a few months ago and am still learning how to run it compared to my old morso. It sure puts off more heat but i have been going through a bunch of wood. It is not great wood, has not been seasoned long enough, i know its not great and i lose some there. But have been thinking about adding the baffle plate and a few bricks to hold it up.is it a clear benefit to not having one even though it may limit how much wood can be stuffed into it for the night? I'd love more heat for less wood!
 
when you added the larger baffle plate does it limit how much wood you can put in the stove overnight? i got my first papa bear a few months ago and am still learning how to run it compared to my old morso. It sure puts off more heat but i have been going through a bunch of wood. It is not great wood, has not been seasoned long enough, i know its not great and i lose some there. But have been thinking about adding the baffle plate and a few bricks to hold it up.is it a clear benefit to not having one even though it may limit how much wood can be stuffed into it for the night? I'd love more heat for less wood!
I would say it has changed it. It is about 12 inches from the front door inner lip up to the baffle plate. As someone who does not do the over night burn. I do not have experience with loading the stove up for the night. I usually go to bed with the stove off.
 
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So for about 90 dollars Canadian. I bought 1 sheet of 1" x 1' x 3' ceramic fibre board plus 7 Full size 2300F insulate bricks.

I cut the board into two 15"-3/4" x 12" sheets

IMG_1045.JPG



I needed to cut the two of the bricks into 6" x 2.5" x 4.5"

the brick at the back could have been 2 inches and a full size brick. I cut it 1.5" and it has a small gap.


This left about 2 inches of gap up to the top of the cooking plate. so 2x16" = about 32. Which is what the flue pipe is.
I added two small fire brick splits to the edges(On top of the ceramic fibre boards). This made it so more of the gases went to the center of the cooking plate(hopefully)
IMG_1044.JPG


IMG_1046.JPG
 
Last edited:
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Easy Livin’ 3000

Minister of Fire
Dec 23, 2015
2,920
SEPA
So for about 90 dollars Canadian. I bought 1 sheet of 1" x 1' x 3' ceramic fibre board plus 7 Full size 2300F insulate bricks.

I cut the board into two 15"-3/4" x 12" sheets

View attachment 274986


I needed to cut the two of the bricks into 6" x 2.5" x 4.5"

the brick at the back could have been 2 inches and a full size brick. I cut it 1.5" and it has a small gap.


This left about 2 inches of gap up to the top of the cooking plate. so 2x16" = about 32. Which is what the flue pipe is.
I added two small fire brick splits to the edges(On top of the ceramic fibre boards). This made it so more of the gases went to the center of the cooking plate(hopefully)
View attachment 274985

View attachment 274987
I like what you are doing. I think I'd have just bought a much cheaper ceramic blanket, since you already have a steel plate for your baffle, but that's water under the bridge now. Your rigid one will last longer and doesn't require a weight.

If you added some stainless reburn tubes for the baffle to sit on and burn the gasses off, that'd be cool too.
 
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I like what you are doing. I think I'd have just bought a much cheaper ceramic blanket, since you already have a steel plate for your baffle, but that's water under the bridge now. Your rigid one will last longer and doesn't require a weight.

If you added some stainless reburn tubes for the baffle to sit on and burn the gasses off, that'd be cool too.
Thanks!

The reason for the only ceramic fibre board. is the metal warped. metal also will hold the heat more which i am trying to get away from. I want most of the heat to be reflected back into the wood/fire to help with a efficient burn.


Small steps. i like changing one thing and than seeing how it will change the stove. I am now noticing the stove operates easily at 1/2 turn where as before i would keep it at 1 turn for a while and than move down to 3/4 turn. It also heats up the chimney really quick with the first fire in the morning. within 5 minutes or so about 3 feet from the top of the stove, the pipe reaches 250*F on the outside. Super impressed.



I am curious about the reburner tubes you are talking about. Do you have any ideas for where the could be installed? The boards are currently supported by the bricks so i have no need to have the reburners support it. At the moment in my mind this stove is temporary at the moment. I am hoping to make a walker cook stove Walker - tiny masonry cook stove. This is the end goal for me!