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Going nuclear

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by Joful, Sep 15, 2012.

  1. Joful

    Joful Minister of Fire

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    This started in another thread, but not wanting to hijack...

    So you throw a large load of small or sappy splits in the stove, atop an established coal bed. It takes off and starts out gassing faster than you ever anticipated. Your secondary system (cat or flutes) goes nuclear. If you have a cat stove, you either open the primary air to cool the cat and watch the firebox temps rise, or you open the bypass damper and close the air control to burn smoke dragon style for 5 - 10 minutes. If you have a non-cat, you probably do something similar (?), or just ride it out.

    The real question is how this situation can be avoided in the first place. You want to load that big firebox full, so you can leave for the day and have the stove cruise for 12 hours.

    Seems to me the only solution is to load up the firebox a little at a time, letting each small armload of splits off-gas for 15 minutes before loading in more, to eliminate the large amount of simultaneous out gassing that leads to the "nuclear" condition.

    Problems I see with this plan are:

    1. You're going to burn a bunch of wood in smoke dragon mode, if you're incrementally filling the firebox over the course of 45 minutes or more. It might be more than an hour after adding your first incremental load before you can re-engage your secondary burn system.

    2. Who has that kind of time before work in the morning?


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  2. Todd

    Todd Minister of Fire

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    Pipe dampers can help slow this down especially with non cats and taller chimneys. Some people have also tweaked with the air supply inlets for more control.
  3. Woody Stover

    Woody Stover Minister of Fire

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    I let the coals burn down pretty low. Then I build a top-down load. I throw big splits in on the coals. I leave some room at the top for a few small splits, pine kindling and a little newspaper. Then I light the top. The air enters my stove above the glass so the top takes the oxygen and burns first, progressing downward in a controlled fashion with controlled out-gassing. Once I got the hang of it, and with pine kindling, it's not much work at all. And the heat is near the top of the stove, where it needs to be to get that area up to temp to facilitate another cat light-off.
  4. rdust

    rdust Minister of Fire

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    I've never had one run away with my current stove, really not even come close to running away. With my Endeavor I would load it full and just ride it out. It would never reach the magically 800* over fire temp but boy would it get close and make you worry for a bit.

    With my Lopi I learned to control it by only loading when the stove was down to coals with stove top in the 250 range,(give or take) pulled all the coals to the front of the stove and loaded n/s. Dragging all the coals to the front and loading e/w would probably work for some stoves but never worked good for me getting a consistent burn. I will say I never gave it enough practice to get it down though since I hate reaching that far into a hot stove to place the rear splits.

    If I would've kept the Endeavor I was planning to modify the secondary air channels so I could control the secondary air coming into the stove.
  5. simple.serf

    simple.serf Feeling the Heat

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    Our stove has never run away for me, though it has for my wife.The cause was small spits on a deep coalbed, because she didn't want to wait for it to die down.

    So you want that big firebox full for a long burn time, right? Big splits or a couple large rounds and some splits are your solution. Small sappy splits aren't going to get you a 12 hr burn time, and can cause the situation you describe.
  6. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Seems you answered your own question! You stated, "So you throw a large load of small or sappy splits in the stove, atop an established coal bed." So there is your answer. That is, you simply do not throw a large load of small or sappy splits into the stove. That stove can be just like your computer. It will do what you tell it to do. If you tell it to go wild by throwing in such junk, it will do so. It is up to you to put the proper fuel in the stove. Do it right and you won't need to sit there for 45 minutes. If everyone had that situation there would be few who would burn wood and that would probably include me. There simply is no need of this sort of thing.

    Putting the right fuel in the stove is no different than putting the right fuel in your car. Poor fuel = poor results. Good fuel = good results.

    One more thing is if that stove does go berserk, look at the draft control. Where is it? If it is set really low, many times giving it a bit more air will take care of the problem. Sure, it sounds goofy, but it does work. We had a case in our own house of the stove trying to overheat. I caught my wife sitting at the stove opening the bypass then closing and opening again. I looked at the draft control and it was set to zero (setting zero to 4). I simply set the draft to 1 and closed the bypass and the stove cooled right down below that maximum of 700 on our stove right away.
  7. begreen

    begreen Mooderator Staff Member

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    We usually hear this term from 1st year wood burners that are not yet familiar with the stove or burning, though a strong burn can happened once or twice a season to experienced stove owners too. The difference being that an inexperienced burner will likely be panicking when the stove top hits 600F, (especially if there is a flue thermometer on the stove top). They'll see the needle creeping into the red "overfire" range and panic. A seasoned wood burner will ride it out, knowing that an occasional foray to 750 or even 800F is not going to harm the stove and it will settle down. Timing is a big part of control. Throw a big load of combustibles on a large, hot 750F coal bed and you are going get instant outgassing which the stove is designed to burn off. A good stove manual explicitly warns against doing this. Choke it off and snuff out the fire and one risks a serious puffback when it reignites.

    Knowing the stove and the wood supply will avoid this. When the coal bed is burned down a bit and the stove stoked with fuel appropriately sized for the stove and desired heating conditions, it'll be fine.
    Remember, the most important nut in the stove is the one who's running it!
  8. Backwoods Savage

    Backwoods Savage Minister of Fire

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    Well stated BeGreen.
  9. n3pro

    n3pro Minister of Fire

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    From someone who had a few of those oops moments. Open the door, shut the secondaries down and get a rush of cool room air will cool it off. The first time for the oops was reloading too soon and underestimating the wood. I thought they were big splits and would take a while to ignite - WRONG!. The second was left the air control too open too long. New stove this year so we'll see if I start the whole "oh crap" cycle over or if I'm smarter now.
  10. begreen

    begreen Mooderator Staff Member

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    Well, yeah, there's that. And yours truly has also been guilty of getting distracted. It got the stove hot, but not to the overfire range of 900F. It depends on the stove. Space out the 602 and leave the air control open too long and you will be smelling hot stove pretty soon. Fortunately the T6 is a bit more forgiving in that regard.

    There are installations where the draft is too strong and even an experienced burner needs to be careful. In that circumstance either the draft needs to be reduced or the air supply to the fire a bit more restricted.
  11. PapaDave

    PapaDave Minister of Fire

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    Uh, yeah, 900.
    That's about the thermo limit, so I'll say that's where it topped out. Yep, that's it.
    Then, I got the stove fixed.
    No glowing of any kind, except the nuclear explosion which required a change of undiewear. J/K;)
    Backwoods Savage likes this.
  12. robertmcw

    robertmcw Member

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    I got mine up to 850 or a little better twice but it did not get red. I got it used so I don’t know what the other owner did. This year I replaced the baffles and the burn tubes and they were a little warped but the top is fine and it has not smoked inside the house.

    I try to keep it from 300 to 500 and I don’t keep it too full with wood.

    Robert
  13. Joful

    Joful Minister of Fire

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    Ahh... so obvious, now! Never thought of just keeping to bigger splits, or even rounds. Keeps the surface area / volume ratio as low as possible, and thus, slows the off-gassing. Interesting to note, though, that I see most of you experienced guys split your wood consistently smaller than I do. In fact, watching you guys got me to start splitting to half the size I had used previously.

    I understand how the top-down method could be a big help here, but again, we were assuming in the OP that one was starting with a deep coal bed (or even a partially burned load). Waiting for the perfect time to reload may be a luxury the self-employed and retirees can afford, but not in this house! It may be 4 hours into a 6 hour burn on a medium load when I realize I need to run out for several hours.
  14. begreen

    begreen Mooderator Staff Member

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    ?? I split mine big, 6-9" splits are fine for the T6. The smaller stuff is for fire starting. Bigger splits burn slower and provide a steadier heat.

    PS: Last I checked, you are the OP. :)
  15. dafattkidd

    dafattkidd Minister of Fire

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    That is one advantage of having a fan on my insert. If I foolishly let the unit get too hot (two or three times last year), I just open the draft and crank the fan on high. Usually within a few minutes the stove top drops significantly and the fire is soon once again controllable.

    6-9" splits? wow. How long do you let those splits stay in the stacks before burning them? I can only imagine it must be two full years for most woods.
  16. blwncrewchief

    blwncrewchief Burning Hunk

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    I think most of the above is pretty much the case. Once you get to know your stove it is pretty easy to know what to do and not to do. Hotter stove and more coals = bigger splits and also what kind of wood. For example load a full load of 4-5" black locust splits with the stove at 400 or so with 2-3" of coals would be ok in my stove. Might go to 600-650 max. But a a full load of 4-5" soft maple or pine at 400+ would be very bad. You also learn some tricks for your setup and needs. Like when it is very cold and I get up in the morning, the house is getting cold, and need to get the stove back up to temp quick, I will throw a small load of small splits (1.5-2.5") of soft maple or pine in and open the air up. They will take off quickly and get the stove temp up quick. I know about exactly what is a safe amount to put in to get the stove up to 500-550. In 20-30 minuets the stove temp is up and the small splits are burning down and starting to coal by the time I sit down with my coffee. I then can load my daytime load and have it cruising in another 15-20 minuets. This is the worst case scenario only when it is very cold but is a way I can get the stove up and running full tilt with a full load in a hour or less in the morning predictably. It is also a good reason I like to keep a variety of wood and split sizes. I think most of us have all made the right of passage with the pucker factor and the windows open when it is snowing or freezing our rear off, cussing at the stove with the door open trying to get it going faster.;sick
  17. Highbeam

    Highbeam Minister of Fire

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    Softwood will be seasoned in one year so long as it is split and stored properly. Size of splits is not a significant factor. I'm going bigger now too for several reasons. Thing is, this means that lots of rounds will go unsplit. Trying to shoot for a 6"+ split can mean a large part of the tree will be too small already. I suppose that is a good thing so long as it can dry out.

    OP can be original poster but in the context I see he meant Original Post.
  18. begreen

    begreen Mooderator Staff Member

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    Yup. It depends on the wood. Doug fir dries pretty quickly and has a high oil content so 1 yr works for it. I split maple more toward the 5-7" size, but that is soft maple. Locust I have found to be a very dry wood and given 2 years it's fine. Madrona seems to be ok after the second year too, but typically I am splitting smaller trees of that species so the madrona splits are more like 4-6".

    Good point about the fan. It'll take the stove top down about 100 degrees in pretty short order.
  19. Backwoods Savage

    Backwoods Savage Minister of Fire

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    I do not see that as a problem at all. If that is all you can get is a 6 hour burn, then fill it up if you have to run out. Just don't fill it with kindling sized pieces. This is also a good time to put a round or two in the stove.
  20. lopiliberty

    lopiliberty Minister of Fire

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    On a full load my liberty tops out at around 750 for and hour or maybe a little longer depending on coal bed split size ect. When it gets close to the 800 degree over fire temp i just turn the fan on close the air all the way if its not already and ride it out. Only reached 900 or above because thats all the higher the thermometer goes one time in 2 years and that was a little scary, I just shut her down and turned the fan on high and it came down to 600 in about 10 minutes. I've come to realize as a woodburner, some times your stove is going to go nuclear, and the best thing is to know what to do and not to panic!
  21. WellSeasoned

    WellSeasoned Guest

    This is all a really good conversation. I am still a newbie as well, with only 1 year of burning under my belt. By the end of last years burning season, I felt pretty comfortable with everything, but I still wonder about what BeGreen explained in an earlier post about back puffing. I experienced this last year when I put splits on a coal bed, waited for them to ignite, they took a bit and finally did when I opened the door and WOOSH!! a fireball nearly burnt my face off. It was the extra air needed when I opened the door with all those gases present in the stove, scared the h-e -double- hockeysticks outta me. What did I do wrong, and how should I go about this next time? Its it ok to put splits on a small coal bed with the air mostly closed on a non cat stove, if say I got a call, had to leave, for maybe 6 hours...or is this bad??
  22. Backwoods Savage

    Backwoods Savage Minister of Fire

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    WellSeasoned, whenever we put wood in the stove, the draft goes full open. This should be done no matter what kind of stove you have. If you follow this you should have no problem with the back puffing. As you now know, it was the lack of air that caused the log to not ignite until you gave it air by opening the firebox door.

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