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Added a baffle to Grandma Bear Fisher Stove (updated with 2ndary burn idea)

Post in 'Classic Wood Stove Forums (prior to approx. 1993)' started by pen, Dec 19, 2008.

  1. Peter B.

    Peter B. Feeling the Heat

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    I seem to have made a bad habit of 'borrowing' other people's threads, for which I apologise...

    --

    Todd:

    I first modified my stove when catalysts were 'the rage'. I'm now inclined to think an effective secondary air system is both more 'elegant' and better suited to the average (read: casual) wood burner.

    Introducing another control (bypass or catalyst slide) to normal operation is clunky if you can achieve nearly the same effect without.

    But I don't plan to give up my own catalyst any time soon.

    Peter B.

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  2. pen

    pen There are some who call me...mod. Staff Member

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    All ideas are welcome. I do appreciate the suggestions and see no reason to stop here!

    pen
  3. bokehman

    bokehman Feeling the Heat

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    Pen, going out the flue exit is fine if you don't want to drill the stove. If the pressure outside the stove is greater than inside the stove (which of course it is once there is a fire burning) air will enter the stove through those pipes. If you wanted to be fanatical you could terminate the secondary air entry at a lower point than the fire (just to satisfy the doubters). You don't need to regulate the secondary air. It's not regulated on EPA stoves except by the hole size. For the pipe I would go with mild steel, not iron. It's easier to work with; you can weld it with mig, tig, or arc; and it bends really easily. On my insert there are 2 rows of tubes, one at the back of the baffle (like your diagram) with ten 1/16" holes, and another along the leading edge of the baffle with ten 1/16" and ten 3/16" holes.
  4. glfporsche

    glfporsche New Member

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    Hi, I'm new to this forum.

    Secondary air tubes are totally doable. Here's the installation I did on my old Lopi.

    http://www.glfporsche.smugmug.com/gallery/6450885_NdHjA

    You'll notice the air inlet is the highest point in the system. Smoke will come out of the inlets, but ONLY when the doors are OPEN. To comment on the previous debate; once the stove is closed up the air pressure inside the stove is LOWER than the surrounding air. ANY opening will allow the higher pressure surrounding air to push its way in, no matter where the opening is located. Notice I did not say it "draws air in". You can not pull on air any more than you can push on a rope. In my case the inlet air tubes let air in once the doors are shut, but will let smoke out when the doors are open.

    As a side note: the inlet tubes shown in the pictures (top tube that bends 90 degrees into the box beam) are very undersized. I have since cut very large holes into each side of the stove leading into the box beam, and welded a vertical 1x2 on each side to feed the holes with air. The air now comes in at the bottom of the stove, so there is no smoking problem when the doors are opened. The resultant secondary combustion is impressive. I'll have to post some flame picts. You can see by the chimney shots, it burns quite clean.

    BTW, does anyone know what kind of Lopi this is? I got it used. It was built in 1983, but that's all I know.

    Kris

    Modified Lopi
    Quadrafire 3100i
  5. jacksnipe

    jacksnipe Member

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    Actually 2 of these fittings would need to be installed, one on each side of the firebox. The fittings would be connected to manifolds that sit on top of the firebrick retainers. Running between these 2 manifolds would be 3 - 4 1" diameter perforated tubes. The manifolds would be closed on the both ends, I was thinking about a manifolds that are 1 1/2" x 3" x 18" long..
    I didn't know that the secondary air had to be injected from beneath the fire. If the air doesn't need to be regulated then other options could be considered.
  6. bokehman

    bokehman Feeling the Heat

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    Not beneath the fire. It's above the fire, just below the baffle, in the smoke path.
  7. glfporsche

    glfporsche New Member

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    Just a bit of advice after having gone through this. Give the secondary manafold more air than you think you need. You can always damp it down later. I would shoot for equaling the primiary air supply. 1/2 inch NPT might not be enough.

    Kris
  8. Peter B.

    Peter B. Feeling the Heat

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    glfporsche wrote:

    >Secondary air tubes are totally doable. Here’s the installation I did on my old Lopi.

    --

    As I once heard it said: "Too good."

    Do post some burn pics when you can. I'll bet pen (and others as well) will be convinced... if they weren't already.

    Peter B.

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  9. jacksnipe

    jacksnipe Member

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    Very intresting, this is very similar to what I have in mind, although the design that I'm thinking about uses a different approach. You may be right about the 1/2" npt being to small, In looking at your manifold assy, it looks as if it's welded at a slight angle up, to reduce smoke spillage into the room upon opening the door ?
    I was thinking of using cotter pins etc. on each side of the tubes to prevent them from falling out. One question here is, what is the distance from the flue opening in the stove to the top of the baffle material..
  10. fossil

    fossil Accidental Moderator Staff Member

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    Pretty tough to tell from the pics, but it's from the era when Lopi was beginning to understand the direction stoves needed to go. You've got primary air controls beneath the doors, and a secondary air control over the door. In that respect, it's similar to my old M520. The M520 had an 8" collar, and had a firebrick baffle supported by a steel plate high in the rear of the box. The air through those secondary ports served as both airwash and secondary combustion air supply. I'll attach a pic of it. Don't have the stove anymore, but I still have the original owner's manual. If you'd like to have it, I'll be happy to send it to you. Rick

    Attached Files:

  11. pen

    pen There are some who call me...mod. Staff Member

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    That is some beautiful work. You obviously are more than a hobbiest with metal?

    The smoking when the doors open is an issue that I was worried about for 2 reasons. 1, I and my wife LOVE the wood stove but do not want to smell like smoke. We each worth with people that live in homes who do not burn properly or have a draft issue causing back smoking and it is obvious and unpleasant. Many people who come to our home comment on the lack of a wood burning smell and are surprised that we burn.

    This is also of concern because I enjoy burning the stove with the doors open and spark screen in place.

    Thank you for showing me how it SHOULD be done!

    pen
  12. pen

    pen There are some who call me...mod. Staff Member

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    Thanks to everyone for the responses and ideas. Here is the impetus for my wanting to install secondary tubes.

    1. The results of this baffle are unbelievable! Where an average load of wood used to use 1/4 of the water in my stove stop steamer, I am not going through 1/2 to 3/4 per burn! An overnight burn will leave just enough to cover the bottom! To heck with debating stove top temperatures, those results speak volumes of the efficiency gained through this setup.

    2. While I love the added heat gained from my wood, what I am not happy with is my flue gases. I now have smoke!!! I never did before except for about 10 minutes after a reload. From then on out, it would be nothing but heat waves. Now, I am getting 30mins on an average load to 60-75 minutes on an overnight load of white smoke from the chimney. All the while the stove is producing killer heat and the chimney is about 350 degrees (normal).

    While I love the added heat my number one goal is safety. I cleaned the chimney upon adding this baffle so that I can check to see accumulation as a result of its addition.

    In the past I get very little build-up in my chimney (a handful after a month of solid burning with this old pre-epa monster). However, my chimney is exterior masonry and the creosote that I did collect would be the second stage variety from the top third of the chimney.

    I have discussed the smoking issue with the metal shop buddy who built this for me, and he believes even with the added smoking that I am going to find less 2nd degree creosote in the chimney since I am no longer needing to use my stove damper and the velocity of my flue gasses will have increased.

    Even if he is correct, the smoking issue bothers me from a smell standpoint (I like my neighbors) and an environmental standpoint (no tree hugger but I don't like making a bigger impact than necessary).

    My thought is that a simple secondary, while it may not be perfect, may add enough extra air in the back of this baffle to help better burn this smoke I am finding.

    If I open both doors with a full load it is amazing to see the fire box FULL of flames and the chimney smoke will immediately clear up. If I add more primary air with the doors closed however I will overfire in no time. I am hoping that a small amount of secondary air in the right spot will make the perfect balance.

    What do ya's think?


    pen
  13. Hogwildz

    Hogwildz Minister of Fire

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    Mayer I am misunderstanding.
    Pen just stated he is not drawing the secondary air from the exhaust flue if I read it correctly, but from an outside source separate from the exhaust. That I can understand.
    Is this drilling you speak or separate from the exhaust gases? Just curious.
  14. jacksnipe

    jacksnipe Member

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    Pen: You mentioned that with the doors closed & the primary air open it shows signs of over firing quite quickly, what signs are evident of over firing
    this bullet proof unit. I have often thought about the ramifications of modifying the Fisher for this reason, I wonder how hot it will run with the baffle installed. The hotest recorded temps I have ever reached were close to 800 on the stove top, this was indeed quite hot but didin't show signs of over firing. I wonder if adding a baffle will increase this to a dangerous level..
    My thoughts are along the lines of running the unit up to say 500 degrees & closing the draft caps to about 3/4 of turn from full closed.
  15. WidowMaker

    WidowMaker Member

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    I like that idea, mind if I borrow it. I might use 3/4 or 1" inlet s though, 1/2 seems a mite small...
  16. pen

    pen There are some who call me...mod. Staff Member

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    I am measuring 600 degrees on the slanted area between the lower and upper levels no problem. Hitting 800 in the middle of the lower plate now where my steamer sits is very possible.

    I have NEVER seen any glowing and intend to keep it that way! I am not afraid of overheating the stove for fear of hurting it but just don't see a need for taking things to that extreme, and I do not need that much heat! I think my current burn temps are plenty and are definitely meeting my heating needs.

    I am not looking for more heat exactly from my unit. More efficiency is really the goal. So if I can get the same heat out of less wood or a longer burn, then that's a bonus. If I can get the same heat and have a cleaner burn, bonus. etc.

    It is not that I did not reach these temperatures without the baffle, what I am finding is that I am maintaining them for a longer period of time now.

    The problem however is my concern regarding the additional smoke I am seeing.

    I think perhaps the smoke clears up in the chimney with the doors open not because I am getting a hotter burn but maybe because the extra air entering the unit is diluting the exhaust gasses? Not sure. With the door open the smoke is much less dense and changes from white to a hint of black.

    Burning well seasoned beech primarily right now. Loaded the stove with 2 year old maple just for comparison tonight and found the same thing.

    pen
  17. karl

    karl Minister of Fire

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    Here's an easy secondary add on to that stove.

    Cut a hole in the bottom rear of the stove. Make the hole the same diameter as the outside diameter of some gas pipe. Use some cutting oil when you drill it out.

    Then run a piece of gas pipe through the hole up the back of the stove, put a 90 on it and run it to close to the front of your baffel. Then put a T on it and run a piece of pipe on each side of it to go across the baffel. Flatten the side of the these pipes a bit with a belt sander to make then easier to drill. Then drill a series of holes in the pipes running across the front.

    The only big problem I see is putting the hole in the bottom of the back of the stove. I'm guessing I would use a 1 inch piece of gas pipe, and that hole would be tough to cut. You might need to use a torch and then you could seal any gaps with stove cement.
  18. Hogwildz

    Hogwildz Minister of Fire

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    Since you already have the angle iron framed out for the baffle, why not make a secondary baffle like PE and some other manufacturers make?
  19. pen

    pen There are some who call me...mod. Staff Member

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    Are you talking about a drilled baffle plate that would rest just below this one?

    pen
  20. hydrology_joe

    hydrology_joe New Member

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    Impressive handiwork! I am curious, what is the white material on top of the secondaries? It almost looks like a foam. (or impressively white bricks)

    I have an old Fisher insert that I'd like to add secondaries to. What spacing did you use for your holes? How did you determine that? Besides the inlet size, what would you do differently?
  21. hydrology_joe

    hydrology_joe New Member

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    I'm learning vicariously through Pen's efforts here before I attempt my mods. This may be an easier option than fabricating secondaries. Could you elaborate?
  22. glfporsche

    glfporsche New Member

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    I don't want to drag us too far from Pen's mods; but to answer a few questions: My secondary air tubes are in fact 3/4 inch. The baffle is McMasterCarr part number 93595K73. It is a ceramic board made of aluminia and silica. It has the consistancy of foam, very low density and soft, but it can take 2300 degrees F, and is a very poor conductor which means it reflects heat back into the fire box. It is mounted at an angle, which I regret as it makes it harder to get the wood pushed all the way back. The baffle is about 4 inches from the inlet of the stove pipe.

    To comment on Pen's conserns on adding more secondary air, and that leading to overfire. I actually believe that you can add more secondary air right at the top of the baffle and this will burn off the smoke but will not increase your temps all that much, and not increase your burn rate. The bulk of the air that's injected right at the baffle does not seem to get down to the main fire and thus does not seem to increase the burn rate.

    I more than quadroupled my secondary air supply when going to the stainless tubes. I use a little less primary air now but not four times less, and the burn rate is about the same. Actually, I find it harder to overfire now.

    I've updated with some flame picts: http://glfporsche.smugmug.com/gallery/6450885_NdHjA

    If you look closely, the picts at the bottom are with the stainless tubes and much increased secondary air. You can see a contionus ribbon of flame coming off the rear most tube. The secondary air enters the at the passage welded (poorly) to the side of the stove.

    Kris
  23. glfporsche

    glfporsche New Member

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    Rick,

    Yea, I think you got it. I think my Lopi I an insert version of the stove you are talking about. It's a beast!

    Kris
  24. brooktrout

    brooktrout New Member

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    I just wanted to say congrats on modifying your stove and especially for getting so many responses and ideas. All three times I tried to bring this up all I got were a bunch of pessimists saying don't mess with your stove. :mad:
  25. Peter B.

    Peter B. Feeling the Heat

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    Hogwildz wrote:

    >Mayer I am misunderstanding.
    >Pen just stated he is not drawing the secondary air from the exhaust flue
    >if I read it correctly, but from an outside source separate from the
    >exhaust. That I can understand.
    >Is this drilling you speak or separate from the exhaust gases? Just curious.

    I think you did misunderstand me, Hogwildz.

    --

    This still seems relevant to the thread so... I offer this simple example, which (I think) illustrates the idea.

    If you drill a hole in your flue pipe and you have adequate draft, room air will be drawn into the flue through the hole.

    If you put a tube of some kind partway through the hole in the flue (and the fit is tight), the tube will draw room air into the flue.

    If you extend the tube through the hole in the flue down into the stove, it will still draw air... into the stove.

    The extended tube will have at least a minimal heating effect on the air flowing through it. This is, in effect, a very primitive secondary air supply.

    It also avoids drilling holes in the stove itself... which pen said he was reluctant to do.

    In my case, instead of drilling through the flue, I used an existing hole near the stove outlet flange (one of three such holes that originally could be opened or closed to help slow an overdraft). I sealed this hole to a 3/4" copper elbow (open to the room), and added a length of copper tube down into the stove. Again it's a rather primitive arrangement, but in fact, it helps some. My stove doesn't have a glass door, so I can't see what's happening inside, but with all other drafts closed, under the right conditions, I can hear flame igniting from the air fed through the secondary.

    Peter B.

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