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Interesting behavior in the 30

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by herdbull, Dec 1, 2012.

  1. herdbull

    herdbull Member

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    So I wanted to throw this out there to the wood burning gods and see what else I can learn. In terms of burning wood, wood stoves & stove behavior I am still pretty green and want to learn. It will only help me become a better more efficient burner.

    This scenario has happened twice to me in the last month or so and it has me curious as to what, why & how. I'll do my best to explain things and if I left anything out just holler.

    This a typical nighttime load that easily gets me through 8-9 hours with good heat and big cunks of red hot coals in the morning.

    Roughly 9:45pm, stove top temp 250-300, rake coals forward, open air all the way, load N/S with what I would call roughly a 3/4 load. Somewhere in the neighborhood of 8-10 splits. They are a tad short as they were cut for a different stove so they don't fill the box all the way to the front and they are not loaded tight up against the secondaries.

    By 10:00pm load has started to burn quite well, temps climbing over 400, start to cut back air to say half. No secondaries yet but she's close.

    10-15 mins later air has been cut back to less than 25%, stove top is 600-650, secondaries going. Another 5 mins or so of this and I cut the air all the way back. Temp in the 650-700 degrees. I've also regulated the dog house air, sometimes all the way to nothing.

    One night I was still up about 10 mins later and the secondaries quit firing. Wood has some nice glowing red areas that are doing the "burning" but no flames. Temps still in the 675 range. 5 mins pass, 10 mins pass..... the secondaries never fire again, temps drop 25-50 degrees. It's like all the gasses are building up but not burning.

    The first night I cracked the handle a little and before I had it all the way up she went off like a mini bomb. The second time I cranked the air all the way open and it still took 4-5 mins to get the secondaries to fire.;hm

    I've checked the wood, it's all in the 18% range. Some oak, maple or other harder wood for the longer burns. Do I need to let this go a little longer on say 25% of main air and let the secondaries kick in longer before shutting her down to get more of the wood burning/off gassing? Seems like it's starving for air at the secondaries or temps have dropped too much to make them fire. I dunno (shrug).

    Understanding what's happening will only help me in fixing the problem, if there is a problem. Next time it happens I may just let it do it's thing and stay up and watch. Thanks guys.

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  2. pen

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

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    When that happens to me, I generally blame it on turning the air down too quickly. Sometimes it takes X period of time to close things down for the cruise, other times it takes X +or- Y.

    Even if they are all well seasoned, it may take more or less time simply because of the size / shape of the splits, the air gaps that happened to be left between them, outdoor temps that change the strength of the draft, etc.

    Lots of variables.


    pen
  3. BrowningBAR

    BrowningBAR Minister of Fire

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    Agreed. I have found pulling the air control just a little bit open will get the stove active again without making the temps freak out. When opening and closing the air, if done slowly I feel bumps as the rod moves. When I only want a little more air, one bump is all I go with.

    Not sure if everyone has or feels those bumps on the control rod, but they are there for mine.
  4. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    If you have regulated that doghouse air ya ain't ever gonna be shutting the primary air control all the way down. You will snuff the load eventually every time. When you close off the doghouse air you become the one that has to maintain enough primary air to keep it burning. Not the stove designer. That doghouse air is there to keep people from being able to choke it down and smolder the load.
  5. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    That bump is a bend in the rod. I have always sworn that Bob Pennington put that thing there so he would know where to set the rod without looking during the EPA cert tests. ;lol
  6. etiger2007

    etiger2007 Minister of Fire

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    I have to run my stove during the off gassing process with the air at least 1/4 open or Ill smother it. Maybe try to let the fire recover alittle more before you close the air down more as well. I feel those bumps as well Bar thought I was crazy.
  7. etiger2007

    etiger2007 Minister of Fire

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    Will somebody please post a pic of what a dog house is and the pilot holes they say are located in the front?
  8. corey21

    corey21 Minister of Fire

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    Different stove but if i close mine i end up opening it a smudge and it likes to cruise with it a smudge open.
  9. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    30 nc doghouse.jpg
  10. laynes69

    laynes69 Minister of Fire

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    That's a good question. I've dealt with this on and off with our furnace. In our case it will go from wide open to closed via thermostat. What I found was keeping the primary open a hair helped this problem. I'm glad im seeing others that have dealt with this also, I thought it was just me.
  11. etiger2007

    etiger2007 Minister of Fire

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  12. corey21

    corey21 Minister of Fire

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    I have seen video's and it will act like a blow torch sometimes.
  13. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    I bet if you feel down under the lip in the front of the firebox on the Osburn you will find a hole or two that do the same thing.
  14. etiger2007

    etiger2007 Minister of Fire

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    Not trying to take over the thread but Bart I have looked and there is no holes there, I even moved fire brick. The only holes I see anywhere around the door is up top and thats for the air wash
  15. herdbull

    herdbull Member

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    the holes would be underneath the stove. Take a small mirror and place it under the stove facing up and look for holes. Internally they could be anywhere but I would start with the same method, on a cold stove. Put the mirror inside facing out and look at the backside of the front of the stove.

    As I'm replaying this scenario it is probably a combination of shutting the air down too quick or 2 far. I'll try bumping the primary air a little and by little I think it's only .25" or so. I'm right on the edge, so I think.

    Also when I think about this I'm throwing the "best" wood out of the stack in on these loads. By best they are the bigger more dense pieces I have. I'm loading it full with the most as I have limited time in the morning to get the stove in a burning state that I can repeat the process and head off for work. So I really can't load it to the max at night or I'd have too much heat and coals left in the morning to burn down. So I guess these splits just need a little bit more time to react.

    Thanks for helping and kinda talking me through this.
  16. blwncrewchief

    blwncrewchief Burning Hunk

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    etiger your Osburn may not have doghouse air as my Drolet does not have any either. All the primary air on mine comes from the air wash.

    To the OP. My stove will do that also if I run the temp up too high and choke the air back. Try cutting the air back sooner and slow down your startup. If I want to run at 500-550 I do not let the stove top go over that at the start. If you are using a stove top gauge it is always lagging when you are in start up mode. Now that I have a probe thermometer on double wall it has made running my stove much easier as it shows pretty accurately what is happening in the firebox and is much easier on startup. For a good startup as soon as the secondaries fire I start easing the air back. I can usually go straight to 50% as soon as the secondaries fire. Then maybe 5 minuets to 25% and then ease it down to the final adjustment over the next 5-15 minuets. 90% of the time it likes 1/8-1/4" of air for the long hall. Only time I burn full closed is a full load with temps under 20* with 15' of chimney all double wall.

    What you are seeing is two things are needed to sustain secondary combustion. A high enough temp and a burnable air fuel ratio. You have the temps but what happens is the wood is burned too much on the outside by the hot initial burn, the chimney temp is high causing a strong draft, then the chimney is pulling too much air thru the secondaries for the amount of off gassing when you close the primary that much. This causes it to go into a "lean" condition and stall. If you let it go the chimney will start to cool and the draft will slow down eventually bringing the air fuel ratio back into a burnable range and it will light off. Slow down just a little on the startup, these things do not like sudden quick adjustments for a good burn. When you get enough experience with the stove you will learn what you can get away with by judgement but until then just slow it down a little.

    Here is where you are letting it go too high too fast. When the secondaries fire get a hold of it then. 600+ is too late if you want a lower burn temp. I would say on a fast start like this keep in mind you are probably seeing a 100* lag in the stove top temp. On my stove when I see the secondaries fire on a reload I am usually reading about 400-450* stove top and 500-550* on the flue probe. Holding the flue temp there will bring the stove top up to about 550-600* and hold a nice long cruse between 500-600*. In other words by the time I am seeing around 500* stove top I am about at my final air setting.
    NSDave likes this.
  17. etiger2007

    etiger2007 Minister of Fire

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    Good post Chief.
  18. herdbull

    herdbull Member

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    Chief, I want to thank you so very much. That's one of the most informative posts I've read here in a long time. Technical but still easy enough to follow and uinderstand.

    I feel much wiser now and thank you for the education.
  19. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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