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Modified fisher project... Just thought I'd share.

Post in 'Fisher Stove Information, Parts, History and More' started by mdocod, Nov 12, 2011.

  1. mdocod

    mdocod New Member

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    Greetings Hearth Forums,

    I thought the community here might be interested in the stove project we are working on here.

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    more picts here:

    http://s17.photobucket.com/albums/b72/mdocod/woodstove/

    I believe that the stove is a Fisher Honey Bear Insert type. We decided to convert it into a free standing unit and add an interesting baffle system in an attempt to improve the potential heating capability and efficiency. The stack outside is triple wall insulated stainless duravent and is roughly 20ft tall to reach a height of 2ft over the peak of the house. Through-wall thimble and stove pipe are also duravent brand. The stove is sitting on a pedestal assembled by stacking non-mortared pieces of red stone wall block.

    The stove has been converted to support outside air supply via a 4" duct. We are finding out that 4" was probably more than necessary, however, what's done is done. The original dampers on the exhaust and intake have been removed in favor of using butterfly dampers close to the wall. (very cheesy one currently installed on the air-supply side right now, will probably worry about the exhaust damper later and upgrade the air supply damper to something better/custom at some point.) As you can see, the supply air runs through long ducts that wrap the length of the stove on either side, and are jointed together at the rear. The purpose of this is preheating the charge air, which as I understand should -theoretically- improve the completeness and cleanliness of the burn which should mean more heat and less smoke.

    The custom exhaust baffle/heat-sink is made of 1/4" mild steel plate, and the air supply channels are made from 1/8" plate and angle. The round exhaust on top was a piece we found that seemed close enough to 6" to be made workable. All Metal used was collected from a metal scrapping yard, and was more than paid for by other scrap metal we dropped off there.

    The results, well, I don't have any other wood heating experiences significant enough to compare to, however, we are easily heating a ~2500 sq/ft house with it right now without any trouble so far but the average temps outside have not been too terrible (~40-60F days, ~15-20F nights). The natural drafting characteristics in the house have proven to be very conducive to wood stove heating so far so we are very pleased. I think tonight will be night #4 with the stove installed.

    Eric

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  2. webbie

    webbie Seasoned Moderator Staff Member

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    Thanks for sharing. Definitely some major mods!

    Did you do anything internally to the stove to enhance combustion? There are some threads here somewhere about folks who tuned up the combustion in old Fishers.
  3. begreen

    begreen Mooderator Staff Member

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    Major mods indeed. Will someone kindly pick up Coaly from the floor?

    It'll be interesting to see how it works when cold and how clean the flue stays. Let us know how it works out and thanks for posting about your project.
  4. mdocod

    mdocod New Member

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    Hello Webmaster,

    The combustion chamber is unmodified, in fact, it's likely that the fire bricks are even original- a few of them are cracked but everything is holding in place alright. We did toss around the idea of installing secondary combustion air supply "pipes," which actually wouldn't be too hard to do in theory.. Just some drilling and more cutting/welding and such. For now we are happy enough with the combustion- proper stove burning "etiquette" seems to be enough IMO :)

    ---------------------------

    Hi Begreen,

    I'll certainly update with results in time. I am a bit concerned about flu cleanliness. When burning a small fire, as I am right now, the stove pipe surface temp where it enters the thimble is down to ~150F. The baffle chamber we welded on there pretty consistently seems to provide about a 100-200F drop (surface temps) from bottom to top depending on the state of the fire. We'll have to make a point to burn a roaring hot pile of thin stuff semi-regularly to clean up some of the mess.

    The good news is.. the chimney design is very easy to clean as there is bottom access via a T connection. I just picked up a poly brush for it yesterday and we already have the sweeper "shafts" here so we can probably do that frequently pretty easily ourselves.

    Eric
  5. Danno77

    Danno77 Minister of Fire

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    Um, wow. That sure is...SOMETHING. I can't help but think that your baffle system is only slowing and cooling exhaust gasses and will make a nice place for creosote to build up. How do you plan to clean that baffle out?
  6. mdocod

    mdocod New Member

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    Hello Danno77,

    Slowing and cooling exhaust gases is pretty much the point :) The baffle is a very "high-friction" area for the exhaust, which should extract a lot of heat energy. Granted this will indeed cause faster creosote buildup when burning cooler fires but I'm not too concerned overall...

    It's pretty easy to pull the stove pipe and clean most of the top half of the unit by reaching down in through the top. I figure we should plan on pulling the stove pipe and inspecting and cleaning what we can reach whenever we sweep the chimney. The bottom half will just have to burn off naturally once and awhile or work it's way down into the fire box when we rap on it with a hammer. I suspect we'll have enough hot fires to keep the system pretty safe overall.

    Then again, this is technically a modded experimental unit. As in, I don't even know if such a mod has ever been tried. if it turns out to be a major problem we're just going to buy a modern EPA stove and slap it in there. We'd like to try this one out for awhile though and see how it works.
  7. coaly

    coaly Fisher Moderator Staff Member

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    I'm trying to keep an open mind through this traumatic experience.

    When it starts to smoke as you open the doors, the heat exchanger is plugged.

    I believe access / clean out doors are necessary on the side of the heat exchanger. (Surdiac used an exchanger on the back on their coal stoves, and had 2 clean out plates that filled with fly ash - but an extreme amount of heat came off the exchanger)

    Better check with the US Patent Office. I'm sure Baxter already patented this one. :roll:
  8. begreen

    begreen Mooderator Staff Member

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    Rapidly cooling woodgas to the point of condensing in a pipe is a concern. This is essentially the design of a still. Condensation of creosote happens below about 250F. If you are only seeing 150F at the thimble, I would pull the pipe and check the stack frequently. If there is serious accumulation building I would lop off the top box and modify the firebox burning instead.

    By all means take a look at some of the other old stove mods where a fire deflecting baffle and secondary rack have been added. These are often more successful because they reburn the wasted wood gases rather than just trying to rob the stack of heat. The flue stays clean, less wood is consumed and there's no smoke.

    Here's some examples:
    http://www.hearth.com/econtent/index.php/forums/viewthread/31420/
    http://www.hearth.com/econtent/index.php/forums/viewthread/17993/
  9. mdocod

    mdocod New Member

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    150F was measured at the thimble on the pipe while burning a very small fire in the front 1/3rd of the firebox. That is not flu gas temps, that is surface temps. When normal fires are burned, I get surface temps on the stove pipe in the 250-450F range depending on the state of the fire and how far I let the embers draw down before another cycle. Exhaust is visible as primarily white steam most of the time.

    Unfortunately, I think it's unreasonable to consider an internal baffle mod on a honey bear insert. The fire box is too shallow.
  10. begreen

    begreen Mooderator Staff Member

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    Ah, those temps are better. FWIW I think the Honey Bear's firebox is a lot deeper than most of the stoves we are burning with baffles today. The baffle doesn't need to come all the way to the front. 3/4" of the way can make a nice difference.
  11. CamFan

    CamFan Member

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    WOW,
    I think you are right about what used to be a Honey Bear Insert. How far is the stove from the side and back wall? the clearance on them was 3' from a combustable surface. Be careful it looks closer than that.
  12. mdocod

    mdocod New Member

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    Hi CamFan,

    Thank you for the heads up on the clearance... We didn't have any luck finding any original fisher stove install requirements online. We read the requirements for numerous other stoves and tried to exceed those requirements by ~6-12" or better for the stove and stove pipe. If you have a link to install requirements for these stoves I would very much appreciate it. Keep in mind that the Honey Bear specific requirements are probably not accurate for a free standing installation of one. Almost all stoves and stove pipes we looked up call for 18" clearance, we have ~30" on all clearances.

    The walls beside the stove get pretty warm to the touch when very hot fires are burned, but not "hot," no indication of any danger thus far. We are contemplating building a brick or stone wall in front of the walls there in that corner in the future to act as a thermal mass. Just depends on motivation level.

    Eric
  13. CamFan

    CamFan Member

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    Eric,
    We see things all the time and people want pipe that are not correct installs and we will not sell the pipe to them. Your pipe looks fine just the picture looked closer than 30". I may have a owners man. but I looked for some stuff for others and if I have one it is boxed up. I work full time and at night do service calls and installs ( I install gas logs) so with cold weather I will not get many evenings free. So your best bet on anything in writting will be from Coaly. He is and has a weath of information documented. One day I will go through what I have and what he does not have I should get it to him. He is more interested in all that than I am. I just wish we could start making stoves again :) that is the area of my interest.
    Steve
  14. coaly

    coaly Fisher Moderator Staff Member

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    mdocod,

    Once modified, any stove would loose it's UL rating and be required to be installed by the UL Unlisted codes. (36" with reduction in clearance with heat shield) Stove minimum clearances are "as tested". UL over-fires the stove and monitors temperature of surrounding surfaces.

    You won't find any rear clearance criteria from the manufacturer on your model since it is a "Honey Bear Fireplace Insert" designed to go into a non combustible fireplace. The UL tag specifies "Use only in masonry fireplace". Front, sidewall, and clearance above mantle is shown on the Honey Bear Insert tag below.

    Yours was advertised to "Heat up to 1200 sf". (this was back in the day of R-11 walls and poorly insulated windows)
    There was a 4 legged Honey Bear with lower air intake designed with a mobile home outside air intake kit, and a freestanding pedestal model not certified for mobile home use. These freestanding stoves have a heat shield on the back for a reduced clearance of 12 inches to the rear.
    The Polar Bear Insert is similar to the Honey Bear, but certified for factory fabricated zero clearance fireplace installation with a heating capacity to 1500 sf.
    They all used Pyroceram glass.

    Attached Files:

  15. CamFan

    CamFan Member

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    See I told you he was great! But ask me a question on how to build a Fisher freestanding I can help with that :)
  16. mdocod

    mdocod New Member

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    Hello CamFan and Coaly,

    Thank you both very much for the heads up on this. I guess the rumors about Coaly around here are true!

    I found a PDF that seems to give unlisted installation requirements with nice charts that show the reduced clearances possible with various forms of heat protection. If I install a 3.5" brick wall around the stove, with a 1" air gap between it and the wall, I am under the impression that the 36" clearance requirement drops to 12". I might go ahead and do that so I don't have to move the stove again. It's just way too heavy. The brick would serve multiple benefits anyways.

    Thank You,
    Eric

    ------------------

    [Edit in] Just realised I should post an update regarding the stove as it has been heating the house now for over a week. I'll just edit it into this response.

    The baffle changes the dynamics of the stove pretty dramatically from the way most people use wood stoves. There are benefits and drawbacks for sure.

    --

    Benefits:

    Enormous heating capability. ~1000 sq ft of this ~2500sq ft house still has single pane glass [it slows the wind down] and blown insulation that has settled, We are working our way through it to remedy that problem, but with the stove, those insulation problems are not really a "problem." With outside temps at 15F, it's easy to make it TOO hot in here without the help of any other heat source. With more liberal fuel loads I have no doubt the stove will be able to maintain comfortable temps in this house with outside temps well below 0F.

    Opportunity to extract heat while still burning a clean well aired fire. The baffle extracts a great deal of heat from the exhaust even when the fire is running completely un-dampened and clean- this is how we run it most of the time because it seems to be healthiest for this stove to operate this way. (this is also a drawback... more on this later)

    --

    Drawbacks:
    Maintaining proper exhaust gas temps through to the top of the stack to prevent creosote deposits requires fast burning well aired fires (see how this is a catch 22?).

    Getting the stove pipe heated all the way to the top warm enough to have exhaust gas temps at the top of the stove pipe warm enough to prevent visible steam, and creosote formation on the chimney cap screen, requires sustained burning of a very hot fire for awhile- Often the house gets warmer than I would want when burning this type of fire.
    In the first week- we managed to totally plug the chimney cap screen with creosote. In the last few days, we have made a point to keep a closer eye on the exhaust, and try to hit clear exhaust conditions for awhile with any fire that is built to clean up the top cap.
    Long unattended burns are difficult to make last. Again, with the intent on trying to keep exhaust gas temps up, it's important to run the fire relatively un-dampened. Which means that any fuel that is loaded burns off pretty hot and vigorously.



    ----

    We've inspected the chimney from both top and bottom, and also had a peek inside the top of the custom baffle to see what's going on... Everything looks pretty normal and healthy in those areas. The top of the baffle assembly has normal dry crusty carbon deposits. The chimney has some of this as well. No evidence of creosote condensing out in the chimney or baffle. Just the top cap- where the cold breeze keeps the top cap and screen cold, which is proving t be a prime spot for sticky/oily wood gas to condense out on. Obviously no matter how clean burning the stove is- all wood stoves have intermittent releases of unburnt wood gas- especially on fresh fuel loads.
  17. mdocod

    mdocod New Member

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    Update:

    (see the edit in above from a few days ago to get the larger picture of how things are going)

    Now that we have modified our burning methods to better suit the stove, we are keeping our chimney cap clear and clean without a problem. We've found that the best way to observe the condition of our burns is to look at the under side of the chimney cap lit by a bright flashlight at night. When it is greyish and matte looking, then everything is clear and clean. When it develops a shiny blackish deposit, we know it's time to "clean it out" with a hotter faster burning fire. The insulated triple wall is really proving to be a very good investment for this type modification as it produces enough draft effort to overcome all of the friction we induced with the baffle. Overall it's hard to argue with the performance of the modified stove. I would not suggest such a modification for most users as it would probably not be safe without proper involvement.
  18. mdocod

    mdocod New Member

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    Update:

    Strike my claim that we were able to keep the chimney cap clear. And apply a strike to all other premature claims about clean burning as well.

    We have run into serious problems a few times, with major drafting problems as a result of the chimney cap plugging (actually smoking into the house around stove pipe fittings). Also, we have already had to clean the chimney and pipe and the top of the baffle once, and I suspect we will have to do it again here soon. The baffle system creates a scenario where a lot of material gets deposited in the top baffles and chimney.

    You folks who were suspect of the mod get an A+ for proper intuition on the matter. We were very WRONG to have thought that this would work "really well." This system could never be "sold." It requires far too much continuous maintenance or special burning requirements.

    As we use the stove, we are getting "better" at it, however, we actually got ahold of a good ole "super soaker" squirt gun to use to blast some buildup off the chimney cap as needed.

    We intend to re-modify the stove differently. I think we are going to drop the baffle system down to a single baffle to act as a thick steel flame catch (I don't like the idea of flames shooting up thin wall pipe). We may try for a secondary air feed. Seems to me like a great place to run the "pipes" for secondary air would be from the front top, tapping into our existing outside air "ducts" that wrap the box, along the top of the fire brick, making a "U-shape" that swings around the back. The holes in the pipe that feed the secondary air would be towards the back of the box there, where it is about to enter the exhaust opening. I assume that an insulated shelf would be ideal so we may try something along those lines.

    Main point here is, if you have seen this mod project, and are thinking of doing something like it, I suggest against it.

    Eric
  19. coaly

    coaly Fisher Moderator Staff Member

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    Since my opinion is free, I'm going to give it to you. :)
    Two basic mistakes;
    1.) A straight up chimney with ceiling support box above the stove is more conducive for the best draft.
    2.) This Insert model didn't include a screen for open burning. A fabricated screen for the entire door opening (as required for a clean burn with "Insert" model) will allow clean burning through the baffled heat exchanger and a damper above it would control velocity to keep flue temps in the 250* f range. The full size Insert also has room for the internal baffle plate.
    3.) Thermocouples to monitor temps in the exchanger, connecting pipe and chimney would be advisable to adjust the proper operating temperature.

    Since all the BTU is going to be released in a very short time, cooling fins to increase the surface area of the exchanger may be needed along with a fan to extract the heat. Still not a practical home heater, but you could make the system work with the correct amount of air flow at the correct velocity. (This BTU, about 1,000,000 is commonly needed for hot air baloons, aircraft wing deicing and corn drying, all accomplished with propane at the present. That was part of my LP business before retiring) Extracting the available BTU out of the wood over a longer duration is preferred, and the simplest way to accomplish that was found during UL and EPA lab testing, with the added baffle plate in the latest stoves. You may be happy with a slight modification on a Fisher Tech IV Insert, or TF-88 instead of trying to reinvent the wheel. (slight enough not to destroy the stove) These were Fisher's attempt at an EPA approved stove.
    $300 Craigslist below. Notice the much larger air space between combustion chamber and outer jacket. Like anything else that works really well, they weren't made for long.

    Here's my attempt at the single baffle theory. (stolen from Mr. Fishers design)
    http://www.hearth.com/econtent/index.php/forums/viewthread/82318/
    Now you know why they called him "The Stove King".

    Attached Files:

  20. mdocod

    mdocod New Member

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    Coaly,

    Thank you, seriously, for your contributions to this forum. You are one of those gems. "Rare-earth" sort of stuff that gladly shares the best of the best with no expectation of reward!

    I think you may have identified our problems almost dead on, less the fact that we have over baffled the custom build... If the inserts air supply was designed in accordance with the drafting efforts expected of a "straight up" chimney install, (makes sense being an insert), then we may be able to make this system work better if we mod the air inlets enough to find a proper balance. We may still have problems making this work really well, however, I think that this little tidbit of information may be the "dots connected" that we were not able to do.

    I am very temped now to temporarily try some added air openings.

    Coaly, again....

    I understand that in some cases, you may feel you take a risk participating in a thread, especially one like this. I just want you to know, that no matter what happens, your advise is appreciated. If the house burns down this is MY fault.

    Thank You,
    Eric
  21. CamFan

    CamFan Member

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    Coaly,
    The pictures you posted above, what are you calling that stove? I has Gma IV doors on it.
  22. coaly

    coaly Fisher Moderator Staff Member

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    Another way to increase your intake air; is "Supercharging" your combustion process.
    The "snail shell" type induction fan has a rotating slide type cover to adjust air flow, or variable rheostat to adjust air flow. You may not be able to get enough air through the fire being "normally aspirated" by barometric pressure through the intake area.

    I've thought about fabricating something similar to what you've made by using a second stove above the primary combustion one. This would allow a series of baffle plates inside the upper "chamber" with doors for easy cleaning. A double decker Grandma if you will. (don't worry, the stove I ruin wouldn't be a Fisher, I would take joy destroying a Frontier or Timberline for the project !) The upper most chamber is going to be a creosote factory. Not a problem if daily inspection and probably weekly cleaning is easy. The chimney I figured should be as straight, short, and fast moving as possible, possibly with a draft inducer fan, or air induction fan at the intake to increase velocity where temps drop enough to condensate. The key being moving flue gasses will not adhere to the flue walls. But you don't want it to move fast through the heat exchanger. With a draft inducer, a smaller flue diameter to further increase velocity moving the same amount of flue gasses is possible. Always think basics, baffle plate for clean combustion, slow through the exchanger, fast up the chimney. Another possibility is a venturi at the top; high velocity = lowest pressure to evacuate any water vapor in the stack.
    This moving air principal is used in extreme cold temps to prevent condensation on windows. A fan on the window sill constantly moves the warm moisture laden air over the glass preventing condensation.

    The thing stopping me from any experimentation is being totally happy with the heat output, fast combustion when required of a long narrow firebox, 6 inch flue, and cooking capability of the Papa Bear. Bob's advice to anyone complicating his stove ? KEEP IT SIMPLE .
  23. coaly

    coaly Fisher Moderator Staff Member

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    Making a few calls, should I buy it?? My wife is gone all day Christmas shopping, so as long as I spend less than her, I'm OK right? :cheese:
  24. CamFan

    CamFan Member

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    I can not tell what it is. I can not see draft caps on the side soI assume in has air coming in under the as fender but the picture does not show much room there. If it comes in under the ash fender it could be a Series IV insert and someone used GmaIV doors. If it is a series IV that is a good insert. It should have a tag on that late of a stove. If you get any better pictures let me know. I do not see space under the stove and it has a larger area above the stove than I would be used to seeing. I have those drawings :)
    Steve
  25. mdocod

    mdocod New Member

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    Hello Coaly,

    Again, some great insight here.

    I take some comfort in the fact that you have considered similar build concepts. (sucking all the heat out). Perhaps we aren't on as bad a path as I was beginning to think we were on. I see some major merit in extracting more heat. In my experience thus far, it seems like, with the exception of when the outside temps are really pushing into the negatives, this can heat the house to comfortable levels or beyond, in fact, it overheats the house when burned "properly" almost any time it is used unless the temp outside is down in the single digits or less. That's ~2500sq-ft heating!

    Your ideas of using some forced draft, etc, may actually make the stove more usable/livable in circumstances where "medium" heat is required. I am definitely going to experiment with increasing air supply before we go tearing our mod to shreds now. We'll try opening up the air supply hole sizes for starters I think.

    Thank You,
    Eric

    PS: I almost feel guilty about having "done this" to a Fisher stove given your liking for them. I hope you don't take any offense to our mutilation modulation operation.

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