Improving Grandma Bear

[rtrev37]

Hello Fisher wood stove lovers,
I have a Grandma Bear Fisher wood stove as well for over 15 years. I have modified it for a better burn by also adding a baffle plate. ever since it has burned a lot better. However, each year I look for different things that I can do to make it even better. So far, modification #2, after the baffle addition, I have decided to decrease the burn chamber size by adding an extra layer of fire brick on the bottom, in order to increase the height towards the baffle to decrease the burn chamber. The reason for this was because I found the original burn chamber extremely large which required lots of wood to fill completely yet only give me 2 hours of burn time before reloading. At that rate, I was going thru so much cord of wood, it just made no sense. I figured most new modern stoves have small chambers of 2.4 cubic in volume so why not decrease the size and see what happens. In doing so, I found that I could burn with less wood and at a hotter temp while also burning cleaner simply because the chamber was smaller and would burn most gases before escaping out the flue pipe. modification #3; install a flue pipe damper. I think this was the best of all modifications. Now with the damper and a smaller chamber, I get a fire that will last 4-5 hours before reloading, while burning cleaner simply be closing the damper and controlling the draft and how fast it would burn. so between the damper and the front air intake, I have much more control of the fire. Oh #4, I also added a door seal simply because my Fisher did not pass the dollar test if you know what that is. Simply place a dollar on your door, close the door tight and attempt to slide the dollar off. If it slides off, it means your doors are not air tight and you should invest in placing some type of door seal; which I did.

So far, I get hotter and cleaner burns with a longer time between reloads. It would hover around 500 deg for about a hour and slowly decline to 250 at which time I would reload between 200-250, depending on the house tempt. Although each year I always consider getting a new EPA stove to save even more on wood and increase the reloading time to every 10 hours, I never reach the point of making the move simply because I had modified My Fisher which I love and understand over a new stove that would be unpredictable in its performance. the problem here is having a small house fo about 1,400 sg ft yet wanting an extra large wood stove like the Drolet HT2000. I would hate to get a stove that is rated for a 1,800 sq ft and find that it does not heat my whole house like my Fisher or that it performs about the same would be disappointing. However, getting the HT2000 may be too large and run me out my house due to the intense heat and low ceiling. so maybe for my next house I will get the HT2000 and just keep playing with the Fisher for further improvements in making the burn to last longer, keeping the heat to hover at 500 deg longer and some how keep using less wood each year as it has already occurred. Now looking into
1. secondary burn, and
2.Maybe removing the second layer of bricks originally installed and see how that works with the stove pipe damper which was a major contributor towards a longer burn time. Possibly, this time I may get an even longer burn time while requiring to add more wood since the burn chamber is now one brick layer lower. Adding more wood is a good trade off for a longer burn time, as its required for all extra large stoves of 3.4 cubic ft fire box or bigger.

I'll post picks if anyone is interested in seeing what I have.

 

[mark cline]

Here is a link to my grandma bear retrofit with secondary air . This had performed better than I could ever imagine. https://www.hearth.com/talk/threads...with-secondary-air.140515/page-2#post-2272700

 

[coaly]

Welcome to the Forum;
Pics would be great to show the door type and pipe configuration.

2 hour burn time is waaay off. That stove should have enough coals after 8 hours to restart easily. After burning 24/7 for a few days you should have enough coals and charcoal in the back to rake it forward and reload at 5 or 6 PM (last loaded before bed the night before). I presume this is seasoned hard wood?

The baffle is adjusted for the chimney, not the stove. Chimney size and connector pipe configuration are needed to give you an idea of baffle size and smoke space adjustment.

A damper is required for your Grandma Bear. In the case of an extremely large chimney, you may not need to use it much with doors closed, but with doors open in Fireplace Mode with screen in place the flue damper becomes the only air control you have, and is the reason it is required. With doors closed it is an overdraft control to slow the velocity of rising gasses. This in turn slows the incoming air. You can't do that with a chimney flue much larger than the stove outlet.

Raising the firebed does two negative things. It decreases firebox size / wood load and raises the bottom closer to the incoming air. You want to burn on 1 inch of ash and slow the fire by lowering it to prevent direct air from the fire bottom allowing coals to starve for oxygen to create charcoal, and slow the burn. Your air dampers should only be open 1/2 to 1 turn, possibly less with gasket applied to door seal. You prevent any secondary combustion of gasses by using gasket material. It should only be added if the fire burns with flame or does not go out with dampers closed.
The door handle angle of the right door should match the left door without gasket and be considered air tight. Hinges and pins can wear and some may need gasket material if there is room for a strip of cardboard in the door seal channel that allows door to close properly. Only flat gasket should be used. There is no clearance for gasket material as built.

 

[rtrev37]

Welcome to the Forum;
Pics would be great to show the door type and pipe configuration.

2 hour burn time is waaay off. That stove should have enough coals after 8 hours to restart easily. After burning 24/7 for a few days you should have enough coals and charcoal in the back to rake it forward and reload at 5 or 6 PM (last loaded before bed the night before). I presume this is seasoned hard wood?

The baffle is adjusted for the chimney, not the stove. Chimney size and connector pipe configuration are needed to give you an idea of baffle size and smoke space adjustment.

A damper is required for your Grandma Bear. In the case of an extremely large chimney, you may not need to use it much with doors closed, but with doors open in Fireplace Mode with screen in place the flue damper becomes the only air control you have, and is the reason it is required. With doors closed it is an overdraft control to slow the velocity of rising gasses. This in turn slows the incoming air. You can't do that with a chimney flue much larger than the stove outlet.

Raising the firebed does two negative things. It decreases firebox size / wood load and raises the bottom closer to the incoming air. You want to burn on 1 inch of ash and slow the fire by lowering it to prevent direct air from the fire bottom allowing coals to starve for oxygen to create charcoal, and slow the burn. Your air dampers should only be open 1/2 to 1 turn, possibly less with gasket applied to door seal. You prevent any secondary combustion of gasses by using gasket material. It should only be added if the fire burns with flame or does not go out with dampers closed.
The door handle angle of the right door should match the left door without gasket and be considered air tight. Hinges and pins can wear and some may need gasket material if there is room for a strip of cardboard in the door seal channel that allows door to close properly. Only flat gasket should be used. There is no clearance for gasket material as built.

Thank you for the extra info. Never thought about raising the bottom being closer to the air intake as a negative. This winter I will remove the extra layer from the bottom and try it as it was originally. However, adding the extra layer was intentional because I did want a smaller burn chamber due to burning too much wood for way too little time. My chimney line is about the same size as my outlet of 8 inches with a steel lining. Its an exterior masonry chimney.

I have good draft on my chimney line and sometimes it seem like it was too much only because I was going thru wood too quickly and on windy days, I can hear that suction pulling. Yes I use seasoned dried wood yet would go thru 4 -5 racks of wood in one winter. This past winter I went thru only 2 1/2 rack of 4x 8 each which is much better after all the modifications.

Door Gasket: I used the flat gasket on the outer edges of the door. I tried inside but was hard to close and just kept the outer edge gasket.

That is amazing if you can achieve long burn time with coal during morning for a re-burn. I defin will lower the burn chamber this winter. please tell me more about your wood stove practice, burn time, wood amount you use and achieving 24/7 burn time? Maybe since I only burn once I get home and never in the morning due to leaving the house unattended for work but even on weekends, its hard to find any coal..its all ashes and tiny bits of coal too small to restart a fire again but this maybe due to a raised burn chamber as you indicated as a negative....

Pics to follow...it's a 2 door system arched on the top. the exhaust is from the back not from the top. However, after reading the actual manual, it said this type of exhaust from the back requires a double wall straight out to the chimney and up. My configuration is different since the exiting clay to the chimney is above the stove as it was when I first purchased the house and left it as is.

 

[coaly]

The double wall pipe is only required with an exterior chimney such as a "Through the Wall" kit that uses an insulated Tee with all metal pipe outside the building. The reason is to have hotter flue gasses enter the exterior chimney after running horizontal through the wall. If you exit the back, elbow up and into a chimney, that is not a horizontal installation that requires double wall pipe.

The arched doors called "Cathedral" were the only door style made after 1980. The model becomes a Series III, but can be built like the old style (I and II) before 1980 with angle iron legs. The new design for 1980 included rear and bottom shields and the corners were bent instead of welded angle iron that becomes the legs. The new style with integral shields and bent corners had a factory "Smoke Shelf Baffle", and was UL listed. This was the baffle I adapted to the single door stoves in the baffle thread. Many fabricators continued to make the old style box with angle iron corners for use on a non-combustible hearth where a UL listed stove wasn't necessary at the time. they were $100 cheaper and very common.

When you build a fire, open draft caps a few turns with flue damper wide open. When kindling starts, if it tends to roar up the stack, slowly close damper until roar stops to slow draft. This is not the time to slow the fire by closing intake air dampers. Slowing the draft allows more heat inside the stove to preheat wood to ignite instead of it roaring up the chimney. Place larger wood on top and as it catches, close air intakes to 1 /12 to 2 turns until established. Close down to about 1 turn or less for desired heat output. You will notice in the morning it will burn down to fine ash in the front at air intakes. You will have more coals and charcoal towards the back where it doesn't get as much air. When ash builds up over 1 inch deep, each morning remove some ash from the front only. Then rake the coals and charcoal ahead to build a new fire on. Charcoal has a very low ignition temperature and it should take right off. This method allows continuous burning without letting the fire die for ash removal. I have always had someone home to tend the fire when I wasn't there, and it is our only heat source. The double doors were designed for fire viewing and are a freestanding fireplace that loads sideways. The Bear Series which are much deeper and narrow actually fit wood much better and the design is much better to get air between the logs as well as a longer burn since air doesn't get to the back as easy overnight. That is the trade off for fire viewing, so if that isn't a priority, a Mama Bear is the same size firebox with 6 inch outlet for much better efficiency. (the efficiency is due also to the smaller chimney requiring far less wasted heat to be left up)

 

[Piney]

2 hour burn time is waaay off. That stove should have enough coals after 8 hours to restart easily. After burning 24/7 for a few days you should have enough coals and charcoal in the back to rake it forward and reload firebed does two negative things. It decreases firebox size / wood load and raises the bottom closer to the incoming air. You want to burn on 1 inch of ash and slow the fire by lowering it to prevent direct air from the fire bottom allowing coals to starve for oxygen to create charcoal, and slow the burn. Your air dampers should only be open 1/2 to 1 turn, possibly less with gasket applied to door seal. You prevent any secondary combustion of gasses by using gasket material. It should only be added if the fire burns with flame or does not go out with dampers closed.
.

What coaly said. Though this time of year we burn with the vent caps closed (once the fire is going). We don't go to half, 1 or 1.5 turns open until it is -20, -30 or -40. I know every grandma is dif in use depending on fuel, chimney, burn habits etc. We have been burning 24/7 for a while now as temps are hovering around freezing. But that's not really cold. The children still play outsude in shirt sleeves. One of them in sandals or bare feet. It's against the rules but, hey, try to stop them.....
I can't see the 2 hour burn unless minimal fuel is used and/or it us a 'one off' fire lit in a fully cold stove OR vent caps are very much open?

 

[rtrev37]

Correction: I have the GrandPa Bear III 1980 version with the cathedral doors as Coaley stated. Here are some pics of my GPB wood stove.

FIREBRICKS: last year I had added some firebrick on top of the stove to retain more heat after the fire cooled down and to prevent the top of the stove from over heating my low ceiling. I found that after the stove dropped below the 200 degree mark, the bricks were still radiating at the 350 degree mark when checked with a heat gun sensor. I am not sure if I will continue to do the same this year because that was an experimented that worked well but the trade off would be less heat radiating into the home. The brick on the upper and back portion of the stove was NOT necessary since the heat output was less and the brick was not as hot as the lower portions-so that will be removed this winter.

BAFFLE: Inside the firebox, I have a fabricated 5/16" baffle steel. The length is 17" long and 12" wide in the front with the sides cut back 6" simply because it was too wide to get the steel baffle into the firebox. The sides are 9" long from back to front while the center is 17" long. The purpose for the 17" was to lessen the heat output to the top of the stove due to my low ceiling and it did just fine and even better with the firebrick on top. The heat output no longer affects the ceiling or any furniture or item to its sides or back. Looking to experiment with a new Baffle about 13"-15" long to expose the top of the stove a little more and get extra heat to see how that works. Since I can now control the heat output from the top of the stove with the firebricks on top of the stove, I want to get a little more heat direct to the top in order to get more heat into the home. I will use a card-board box to experiment and determine the exact size before placing the order. The present steel baffle bent over the years but I just turned it backwards or upside down and the arch is now on the top, with @ 2" clearance from the top of the stove; although it looks like its touching in the pic. I also added a cheap 16 gauge piece of steel sheet across the top of the baffle to close-off the wide opening and let the smoke travel longer towards the front and burn before leaving the firebox.

SECOND LAYEROF FIREBRICKS INSIE THE FIREBOX: The second layer of bricks at the bottom will be removed this winter, as recommended, and will see how that works out. it was originally placed to decrease the firebox so that it will burn hotter and more complete, which it did. I had less smoke coming out the chimney and could see the smoke burning off as it rolled up the baffle to escape the death chamber. Although the only time I would see smoke is during the start up. After 300 degrees or more, smoke was none existent or very little.

However, the ability to keep a bed of coal was difficult due to it being at the same height as the air supply going into the firebox and leaving no coal for a restart. The only time plenty of coal was left was by completely closing one side (one or the two spinners). So if I closed the right side but kept the left side partially opened, the large amount of coal would be on the right side. This winter, I will remove the second layer and experiment with different strategies in keeping the coal in while extending the burn time.

DAMPER: You can also see the damper on the stove pipe which has increased the burn time for me this year while using less wood. Although we did not have a cold winter last year, I will compare the wood usage this year to that of last year as well. Definitely, the use of the damper increased my burn time since that was the last modification and burn time noted.

Concluding IDEA: The problem with the new EPA stove is simply the inability to play and experiment as we do with older wood stoves in making it better.

 

[coaly]

Thanks for the updates, pics and stove model correction.
I experimented with firebrick like that on my Kitchen Queen large top cookstove. Better without.
The theory is the BTU output is calculated by the temperature of each square inch of radiating surface. So if you were to line the entire firebox, you would have a hotter, cleaner burning fire but prevent the outer surface from getting as hot, reducing BTU output. So the more heat you can radiate from the steel into the building, the better. If you need to get the heat off the top due to lower ceiling clearance use a fan. Blowing cool air from floor level under and behind the stove will push the lighter hot air out away from the stove towards the front. Putting a fan behind the stove trying to move the hot air only heats up the fan and is more difficult moving hot less dense air into denser cooler air. Move the cool air towards the hot to take the heat away from the stove.
You should be averaging 8 to 10 hour burns, getting heat out of it to heat up to 2000 sf.over 6 hours.

What size (diameter) is your chimney flue?? Seems like it may be too large requiring you to leave too much up, reducing the heating capacity of the stove. That stove should be driving you out of a 1400 sf home.
That is another huge factor comparing newer stoves that require smaller more efficient chimneys. People reline their flue with a smaller diameter insulated flue and change to a new stove claiming they gained so much efficiency, where the chimney has a lot to do with the heat loss they were experiencing with their old stove.

 

[Todd67]

You've been given some great tips on getting more out of your grandma bear.

Interesting topic and discussion. I'm glad I haven't had to modify my mama bear, other than adding a baffle plate.

 

[rtrev37]

Hello Fisher Lovers, I upgrade my papa bear baffle to a 3/8 inch steel with the dimensions of 26.5 wide by 15 inch deep. I had to cut back a 2"x2" corner notch to be able to get it in. The 3/8 inch baffle is quite heavy and took some muscling to get it in there. I also added a fire blanket with the same width but the depth was 16" or 17" to down slope it at the edge in hopes to slow down the smoke and having it burn before exiting. I thought this would interfere with the draft, but not at all. I removed the second layer of firebricks I placed in the bottom and now have a 2.8 cubic ft fire book. I also added some home made air tubes as an experiment but not sure if it is working or not. I had turn the stove on yesterday and reached a 7 hour burn time before reading 120 degrees. after 5 hours, it was down to 210 degree and this was with a small half load or a little less due to not requiring so much heat. So far it has been a success and will report after I am in full daily use and get a full load in there and see how long that will last. I can only think it will last longer tan the 7 hours with a half load or less but then again is was not a very cold day either which may or may not affect the burn time.

One thing I did notice was the ability to completely close the right side draft and more than 3/4 on the left or more without affecting the heat output. temperature remained steady for a long while. Since the firebox is still getting air from the tubes, closing the drafts was not a problem and it been smoke free from what I observed after warming up and before that. I saw some smoke after closing the right draft and the damper but not sure if it was too soon due to putting some wood before starting my count in burn time . Hope to give some more updates once in full swing.

@coaly, I have an 8" flue. I added a steel liner way back and seem to have brought the diameter down to 7 inch but I have never had a problem with the draft on my chimney line. On windy days, I get a strong draft but with the damper that has helped a lot.

Here are some pics of my new 3/8inch baffle compared to the old 1/4 inch baffle. Also the 1 inch fire blanket that goes on top of the baffle with a 2 inch lip at the front. And my air tube experiment pics I used 1/4 tubes but switch to 1/2 inch tubes at the door and up with a reducer in hopes of getting more air into the tubes. This is just an experiment between the 1/4 and the 1/2. Don't know the outcome until its in full use. I did it this way because I am unwilling to make holes and weld anything on my Fisher. I also covered all the extra space around the tube. I wanted air to simply go thru, up the tube and out on top. This limited the amount of air going into the firebox to keep it going or perform secondary burn. But since I cant see it, not sure how well that is working out. However, my burn time has gone up from 2 hours to 7 hours on the same load and if the tubes don't work as secondary burn, they will at least provide some air to the firebox while keeping the draft spinners closed and increasing burning time as note...but will see soon enough

CORRECTION on the old baffle plate. I had mentioned earlier that it was a 5/16 inch plate but them realized after changing it, that it was 1/4 inch. Now I know why it warped. the 5/16 inch plate is very difficult to find and its why I settled for the 3/8 inch although that is better the original size I wanted

 

[rtrev37]

What coaly said. Though this time of year we burn with the vent caps closed (once the fire is going). We don't go to half, 1 or 1.5 turns open until it is -20, -30 or -40. I know every grandma is dif in use depending on fuel, chimney, burn habits etc. We have been burning 24/7 for a while now as temps are hovering around freezing. But that's not really cold. The children still play outsude in shirt sleeves. One of them in sandals or bare feet. It's against the rules but, hey, try to stop them.....
I can't see the 2 hour burn unless minimal fuel is used and/or it us a 'one off' fire lit in a fully cold stove OR vent caps are very much open?

Unfortunately, the 2 hour burn time was with a fully loaded firebox, draft more than 3/4 closed or more......it would go all the way up to 500 degree when measuring from the stove pipe. that would last for about 45 minutes then start dropping....at about 2 hours, it was down to 200 degree or less. at 3 hours, it was hovering above 100 degrees or completely gone with minimal coal and had to reload and restart with a match and paper. Did that for a few years until I decided to either improve it or get ride of it...the biggest improvement was adding a damper...that alone gave me a 4 hour burn time. Now with the new baffle, and fire blanket on top of the baffle which now has given me a 7 hour burn time with less then half a load. I think I put about 3 cut pieces to start the fire then an additional 4 medium size uncut pieces...this is not including the experimental air tubes, since I can't tell it its actually burning the secondary air...at least this was my experience with this Fisher stove. Although some may say that I don't need the damper or the door gasket would be for me to return to what I originally had....it may work for some without it but it sure is much more effective with it for me..

 

[rtrev37]

Here is an update.,..yesterday and today was my first 2 wood stove fire...I have to admit that Coaly was correct in stating that I do not need the damper for my wood stove on the previous post. the wood stove is working so much better with the new baffle and fire blanket on too of it. I am not sure if the air tubes I placed are working or not but the stove has been running at 500 degree for the past 2 hours and now hovering around 440 or so. I decided to engage the damper while at 500 degrees but then realized the chimney started to produce smoke. After opening the damper fully, the smoke stopped and resumed just as it was before closing the damper. it is smoke free and so far getting good burn time compared to last year and the year before that. Just to repeat, two and more years ago, I was getting a three hour burn time from a full box. After 3 hours, it was down to less than 200 degrees. I have no idea how but that was with the vents pretty much close to closing. Last year, after installing the damper, I got a max of 4 hours burn time and maybe 5 before reloading...now, with the new baffle , fire blanket and air tube (which to me seems like its not working), I have a 7 hours burn time or more with a good amount of coal still left. However, the coals left was after engaging the damper and nearly closing all vents before bed time....By morning (9-10 hours after that last fire), there was enough coal to reignite itself and start a new load quickly. since this is all new to me once again due to the changes, I will keep reporting my findings and discoveries.

Problem: There was one major problem during start up and wondered if anyone has a suggestion. I loaded my firebox up and light the fire with 2 pieces of news paper which caught on fast from bottom up. However, the large amount of smoke that it produced before getting up to 400-500 degrees was a little concerning due to the smoke being swept across the yard and towards the neighbors...I think I should have started a small fire and let it get up to temp to then load it, oppose to starting with a full load from the beginning. I think I will try it that way on the next start up, however, it seems like many YouTube start up videos begin with a full load but I might be wrong or maybe its because of the difference between an EPA and none EPA stoves...what's your opinion? I'd like to know...till the next update

 

[coaly]

Start it with some twisted up paper, cardboard and small sticks. Add larger pieces as it catches. Splits will start easier. Lots of air with damper open until it comes up to temp. With practice you'll get minimum smoke.
If neighbors complain, I show them what a piece of hay bale and some chicken bones smell like. NO, don't do that, it is not greenhouse gas friendly. But chicken bones do STINK.

 

[rtrev37]

Start it with some twisted up paper, cardboard and small sticks. Add larger pieces as it catches. Splits will start easier. Lots of air with damper open until it comes up to temp. With practice you'll get minimum smoke.
If neighbors complain, I show them what a piece of hay bale and some chicken bones smell like. NO, don't do that, it is not greenhouse gas friendly. But chicken bones do STINK.

Thank you Coaly. I have been successful starting with the small fire and brining it up to temp before adding bigger logs without smoke whatsoever. What I don't understand is the ability to fire up a none EPA Fisher Wood stove without smoke before and after yet reading about Fisher stoves being a dragon or how an EPA is smokeless..?? I do understand that an EPA stove has an effective secondary burn that will extend burn time but as far as burning smokless is also possible with none EPA stoves. My last two fires after your start up tip has been smokeless and I am very much pleased with this approach to include now starting to burn from top down. I add small pieces of fine wood, place a piece of news paper or two on top and the rest is academics....keep adding a little at a time while allow the previous small load to burn down. So far so good . Thanks again.

 

[coaly]

Excessive smoke is due to not enough air. Many things as well as operator error can cause this. Loading improperly so oxygen doesn't mix with the flammable gasses that are expelled from the wood, closing the air intake too much, closing flue damper too far, improper drafting chimney, or a stove with a poor firebox design. The higher the firebox temperature, basically the cleaner it burns due to burning more particles that become smoke. Firebrick raises the internal firebox temp, and a baffle in the stove raises it as well as allowing more smoke particles to be consumed in the stove. The common way to burn was to close the air down to a minimum fire to prolong the fire overnight, depriving the fire of oxygen to slow it down causing smoke and creosote. Many stoves were also connected to larger chimneys built for fireplaces which have more draft with more heat left up them, but less draft with a more efficient stove. So those large chimneys slowed the fire, smoked and helped to earn the derogatory names you've heard. Burning responsibly decreases smoke as you have found. Do the same things with an EPA certified stove and you have the same smoke, if not worse.

Your design of admitting air at the top for secondary combustion needs many small holes instead of a few large ones. The air coming into the firebox needs to be at a high velocity so it makes it down to the fuel. There is a lot to proper combustion and your design isn't near what it needs to be. The smaller the tube or orifice, the faster the velocity. So larger tubes inside to preheat the incoming air are required, then small outlets to get a blast of air through them. The principal that makes the intake work is the chimney. Not the stove. Rising gasses lighter than outside air rise in the chimney creating a low pressure area in the stove. Like a very slight vacuum. This vacuum is far less than your breath. Atmospheric pressure is higher outside of the stove, so oxygen is PUSHED into the stove intakes. Open flue damper allows higher velocity rising, creating a lower pressure in stove, allowing more air to come in. When primary intake is closed, the only way for atmospheric pressure to get in is through the secondary intake, through tubes and into firebox. As the air moves into stove, you want as much velocity and mixing of oxygen with fuel for more complete combustion. Like an oil burner atomizes fuel with a nozzle, internal combustion engines vaporize the fuel in carburetor or spray a very fine mist through an injector, this is all designed to mix fuel with oxygen. It becomes more critical with solid fuel since stray oxygen particles must come into contact with solid fuel or you get charcoal that has a very low ignition point, but won't burn in the stove due to lack of oxygen. Glass doors are required to view combustion of smoke particles and design, then adjust the proper mix.
To understand the principals of combustion and further reading I suggest picking up "The Wood Burners Encyclopedia" by Jay Shelton on eBay. There are other books listed on the last pages of all Fisher manuals, but that book is the best in my opinion.

 

[rtrev37]

Excessive smoke is due to not enough air. Many things as well as operator error can cause this. Loading improperly so oxygen doesn't mix with the flammable gasses that are expelled from the wood, closing the air intake too much, closing flue damper too far, improper drafting chimney, or a stove with a poor firebox design. The higher the firebox temperature, basically the cleaner it burns due to burning more particles that become smoke. Firebrick raises the internal firebox temp, and a baffle in the stove raises it as well as allowing more smoke particles to be consumed in the stove. The common way to burn was to close the air down to a minimum fire to prolong the fire overnight, depriving the fire of oxygen to slow it down causing smoke and creosote. Many stoves were also connected to larger chimneys built for fireplaces which have more draft with more heat left up them, but less draft with a more efficient stove. So those large chimneys slowed the fire, smoked and helped to earn the derogatory names you've heard. Burning responsibly decreases smoke as you have found. Do the same things with an EPA certified stove and you have the same smoke, if not worse.

Your design of admitting air at the top for secondary combustion needs many small holes instead of a few large ones. The air coming into the firebox needs to be at a high velocity so it makes it down to the fuel. There is a lot to proper combustion and your design isn't near what it needs to be. The smaller the tube or orifice, the faster the velocity. So larger tubes inside to preheat the incoming air are required, then small outlets to get a blast of air through them. The principal that makes the intake work is the chimney. Not the stove. Rising gasses lighter than outside air rise in the chimney creating a low pressure area in the stove. Like a very slight vacuum. This vacuum is far less than your breath. Atmospheric pressure is higher outside of the stove, so oxygen is PUSHED into the stove intakes. Open flue damper allows higher velocity rising, creating a lower pressure in stove, allowing more air to come in. When primary intake is closed, the only way for atmospheric pressure to get in is through the secondary intake, through tubes and into firebox. As the air moves into stove, you want as much velocity and mixing of oxygen with fuel for more complete combustion. Like an oil burner atomizes fuel with a nozzle, internal combustion engines vaporize the fuel in carburetor or spray a very fine mist through an injector, this is all designed to mix fuel with oxygen. It becomes more critical with solid fuel since stray oxygen particles must come into contact with solid fuel or you get charcoal that has a very low ignition point, but won't burn in the stove due to lack of oxygen. Glass doors are required to view combustion of smoke particles and design, then adjust the proper mix.
To understand the principals of combustion and further reading I suggest picking up "The Wood Burners Encyclopedia" by Jay Shelton on eBay. There are other books listed on the last pages of all Fisher manuals, but that book is the best in my opinion.

Hello Coaly, so far a better year then the rest with the new Baffle ALL burns from start to finish is nearly smoke free with exception of those days when I close the doors or flue damper too soon. I have a question and wanted to know your thoughts on this: Today I am experimenting with removing the ceramic fire blanket off the baffle simply because I was curious if doing so will give me more BTU's from the stove. I fired it up and got my usual topped 500F before declining. Question: Do you think the fire blanket reduces the BTUs from the stove with it on? I don't feel any difference without it so far. I figure it will go passed 500 much easier and faster and the top should feel really hot but no difference to me; unless its so slight that its hard to feel that difference. In need of more heat during those cold days in the single digits.