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Inefficiency of burning wet wood

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by M1sterM, Aug 29, 2008.

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  1. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Yuppers- it's interesting that in the kiln you can directly see the effect of burning wet wood. At certain points I put it in there on purpose because the water creates a reducing atmosphere which is good for certain glazes. The kiln is very responsive, and in less than a minute the temp change is visible on a pyrometer I stuck through the roof. The kiln will be in a steadyish climb- throw in fresh wood- it may stop or fall a bit.

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  2. pybyr

    pybyr Minister of Fire

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    when I bought my old house, and before I built my new chimney, the inside of the old chimney was FULL of that glaze creosote based on a prior owner's installation and burning habits.

    from what a knowledgeable person told me, apparently that glaze creosote does not light back on fire easily- but if and when it does, it's like having your chimney turn into a rocket aimed into the ground- and the temperatures it will generate can wreck flue tiles and make the rest of the masonry so hot that any nearby combustibles WILL combust

    I did find ONE chimney sweep who had some sort of powered rooter-brush, and he was able to run that up and down the flue- and removed about a 40 gallon trash-barrel's worth of glaze creosote- then in the form of powdery flakes- from a 25 foot tall chimney.

    when I saw the volume of that glaze creosote that came out, I was very glad it had been removed by mechanical means, not combustion. it was a sight to behold- and it made me a believer in NEVER trying to run a slow smoldery fire, no matter how well-seasoned the wood.
  3. Jay777

    Jay777 New Member

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    I asked this question before, but I'll revisit it here..

    I have ~3 cords of "seasoned" wood, which means that if I use a moisture meter on an exposed surface, it reads 8% on my meter, and if I split it, it pegs the meter at 35% in the middle. I've had the wood myself for 2-3 months, and it was "seasoned" at that point...

    So I think my choices are, burn this wood and screw up my chimney (paying extra to have it cleaned at least once during burning season, since there's no way I'm climbing onto my roof in the middle of winter), or buy some biobricks and save this wood for next year (I can also burn the "junk" kindling-size pieces, I assume, which is a sizeable amount of my total)

    Does that sounds about right?
  4. fossil

    fossil Accidental Moderator Staff Member

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    A meter reading on the outside surface that's been exposed for however long doesn't really tell you beans. You need to split it and measure the moisture content on the newly exposed face of a split, about half way across the split face, right in the "heart" of the wood split. Seems like you just learned that. It's getting late in the season, but you could consider splitting all the wood smaller, piling/stacking it loosely in a location with max exposure to sun/wind, and keeping it dry when weather threatens...dunno what else you could do for it. Rick
  5. Apprentice_GM

    Apprentice_GM Member

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    Yeah AP, as per the others, plenty of pics, especially the exciting ones! I'd like to see the inside of your kiln in various stages of burn. That sidestock.com site for potters and kilns in Oz you posted in one of my earlier threads lead me to research anagama kilns and I found this pic:

    [​IMG]

    Which blows my mind - 1300 degrees celsius! Can you get a pic of your chimney with a massive flame coming out as well? Do you take shifts with people to continue the firing, or lose heaps of sleep? Have fun!
  6. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    jay777:

    I consider a mid-season look down the chimney a must myself. I don't care if you are burning kiln dried wood. In your case the cost of a sweep mid-season has to be less than a season's BioBricks. And you aren't going to be burning the back of the stack from day one. Every day that wood sits with the top covered and sufficient air space between the rows more moisture is wicking out of it. Rain, sleet, snow, summer, winter, hell or high water. Well maybe not if the water is high enough.

    Burn your driest stuff first and put a piece or two of the other stuff in with it after the chimney is heated up and the stove is rolling. The single biggest wood burning sin is putting wet wood in that stove before it is up to temp and the pipe is hot.

    Worst case, start the season with BioWhatevers and keep an eye on your wood. It is getting there.

    And call a sweep and ask if you get a price deal for twice a year service. They are going to be busy this year but not in the dead of winter. And their kids have to eat then just like any other time.
  7. Rockey

    Rockey Minister of Fire

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    Nice pic, although this very well could be where my Mother In Law hails from.

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  8. Jay777

    Jay777 New Member

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    Yes, I know that.. :) The reading on the outside is to prove that the meter works.. It clearly reads very low for the outside of the wood, and if I do a very thin split off a piece it'll read 15-20% inside, and if I split it in half, it always reads 35+. i'm not really looking to split and restack three cords :)

    If I get biobricks it would be replacing a quantity of wood (next year) that I'd otherwise have to pay for, so it's not quite the same as spending $100 or whatever on an extra sweeping. I can get two pallets of bricks for about $660 delivered I think. Obviously I can also mix the two at that point.. use the bricks to bring the thing up to temperature, and then fill it with the wetter wood for an overnight burn. Or whatever.

    I've also got far too much "kindling", so hopefully I can get a number of burns just with that stuff. I don't think the rocks in the pile will burn, but I can try that too.

    Thanks.
  9. Apprentice_GM

    Apprentice_GM Member

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    Ken, yes good point on the differences in red oak, do you actually mean "same genus" or "same species". I thought the point of a species is to precisely identify a particular plant (or animal but lets stick to trees) whereas a genus is like a family or group of similar trees. So "Red Oak" is probably a genus not a species. I will try and find out the latin species name used in the BTU tables I find to ensure like for like. Unless the different Red Oaks you mention are sub-species, but share the same latin name? In which case even if I find BTU tables with the same latin name, it's moot, because of what you pointed out above. Vexing, vexing, I am vexed.

    Also, your point about southern vs northern exposure heat values - are you sure? Do you have some reference I can read? It might make a difference in density therefore mass given volume, but I doubt it would make a difference in heat value given mass, which is how the measurements should be taken (unless, oh no, please don't tell me these tests are done on cords of wood without referencing the density of the wood used please?). I know you said precise measurement doesn't work so I'll settle for imprecise measurements which still might yield some useful info and rule of thumbs.

    I'm getting so worked up by this appalling lack of accurate and scientific experimentation (if what you said and I've implied is the case) that I might have to bloody well go and do the experiments myself. After the Holz Hausen one.
  10. Max Headroom

    Max Headroom Member

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    I've been worrying a little myself, although I think I'm in pretty good shape. Maybe I'm reading too many posts! I've got two cords that seem to be well seasoned based on how it looks and how it sounds. Two more that were cut in the spring and been stacked in single rows all summer that seem to be coming along niceley. I'll probably be dipping into that sometime in February. Now shouldn't the behavior of my stove give me the best indication of how well the wood is seasoned? If it's igniting easily and getting a good secondary burn can I relax just a little? I sure will be glad to get my rookie season under my belt.
  11. Apprentice_GM

    Apprentice_GM Member

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    Haha! :)

    I reckon a pizza would cook quickly in there too if you got peckish during the stoke (or maybe it would explode upon insertion, could add a nice glaze effect)
  12. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    Yep.
  13. Ken45

    Ken45 Minister of Fire

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    I'm not a plant biologist so I guess you are right about genus and species. I used the term loosely.

    It's rare to see the latin names in the BTU tables. More likely to find "hard maple" and "soft maple", whichever those are... Typically wood burners are not precise scientists.

    Well typically wood with a northern exposure grows more slowly and is likely a little tighter and denser (assuming the same species). As for heat value per unit of mass, most tables are per cord. Want to debate what we mean by a cord? (NO, let's not get that one started again!, LOL)

    I just don't think wood is all that precise. A lot of times species hybridize. If you read some of the forestry publications, you'll find that a lot of times totally different species (or genus) marketed together as a common wood.

    Ken
  14. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    I get a kick out of the Forum members that want to get precise numbers for wood stove performance or wood types. Good grief. We set fire to very large weeds in metal boxes to stay warm. :lol:
  15. potter

    potter Feeling the Heat

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    Since the thread went to the pottery topic- here's my pile of bricks......
    if the attachment works.

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  16. Apprentice_GM

    Apprentice_GM Member

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    Well I don't want that, but I do want rough rules of thumb, which really can only be gained with semi-precise measurements. For example, what if measurements showed super-seasoning wood to <5% MC gave a 10-fold increase in heat? I doubt this is the case, but what if it were? It would be worth changing your seasoning habits wouldn't it? (If possible and practical) I mean I have read your threads where you recommend certain models and sizes of fireplaces because they will provide the amount of heat required, and you yourself determined that based on rules, or guidelines which came from measurements. I'm not at all saying that the sizes of fireboxes and sizes of houses have to be precise, or the amount of wood fed into them has to be precise, but again, you can determine guidelines eg 3 cords of pine = 2 cords of oak for heat output (or whatever the ratio) based on measurements, even imprecise measurements. It's only through measurement you can even achieve some types of progress and improvement eg emission reductions. I'm just not satisfied with the statement "get different wood and season longer, it'll burn better" even though I agree with it. What type of different wood? How much longer for seasoning? How much lower does MC need to be? How much better will it burn? I know I have a touch of OCD but I still think it benefits all of us to know some numbers . . . even imprecise ones . . .
  17. Rockey

    Rockey Minister of Fire

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    There is a famous quote in the engineering world "If it can be measured, it can be controlled." It really is just a matter of how motivated you are.
  18. Ken45

    Ken45 Minister of Fire

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    Black locust or hedge. Five years, well covered, off the ground, with high volume fans blowing on it.

    Worth it? Yes. Would or can people do it? I doubt it. There are some people on the forum who have their wood cut, split, stacked 5 years in advance. Then one starts worrying about bugs and deterioration. For most people, a full year's seasoning is more than they can get around to.

    Yes
  19. ScottF

    ScottF New Member

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    Back to the pottery topic again. I know absolutey nothing about it but it is very interesting and have a few laymans questions.

    Are all kilns fired by wood or is that just a historical way of doing it. I would assume most are gas today? I have no idea. I make period furniture with all the original hand tools and love the old way of doing things.

    Do you guys make those beautiful ovid style jugs with the blue writing on them. My wife loves and collects the antique ones but we also love reproduction stuff.

    We went to Williamsburg and saw their kiln for making bricks. It was really cool and interesting.
  20. smokinj

    smokinj Minister of Fire

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    Same here 5 years out, not yet but getting closer! And i have some of that hedge put back for those very cold windy nights
  21. potter

    potter Feeling the Heat

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    Wood firing is just one way people fire pottery.....gas, electric are the other common things. Pots look very different depending on fuel ( and whether it's fired cleanly [oxidation] or with excess fuel [reduction]). Wood fireing deposits ash on the pottery, this ash melts at 2000+ degrees into a glass, this is how the first glazed pots were made.
    The ovoid early american pots that have that pebbly "orange peel" surface were salt glazed- regular salt is tossed into the kiln- it volatizes and fluxes the surface of the clay pottery and makes it's own glaze.
    Don't know much about wood stoves yet- but can talk your ear off about this stuff. :cheese:
  22. Cluttermagnet

    Cluttermagnet Minister of Fire

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    Somewhere in this or a similar thread, we saw a link to an article and chart which answers this question. The chart plots recoverable BTU's vs. wood MC. As I recall, it is about a 2:1 difference (improvement) in recoverable BTU's for 20 percent MC vs. 40 percent. But that misses the obvious overriding factor- creosote formation. Not too bad at 20 percent MC, very bad indeed at 40.
  23. Apprentice_GM

    Apprentice_GM Member

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    Well that would be great. If it's in this thread, I missed it, my apologies. I just did a search and can't find it. Could you point out the link or thread? Cheers!
  24. Adios Pantalones

    Adios Pantalones Minister of Fire

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    I thought I had responded as well... Potter's spot on. Wood firing has enjoyed a small bump in popularity recently. Most potters doing it for a living use gas. Big pottery producers (automated etc.) use gas and oil. Small kilns are often electric, though some great work comes from electric!

    I make a lot of jugs. (Insert joke here) I like the old Americana pieces- I add a little twist in decoration or glaze. Many of those were salt glazed (as noted- gives an orange peel effect)- but that salt or soda also interacts with the bricks in the kiln, so eventually it will need to be repaired/replaced.

    We're getting the remnants of this hurricane right while I'll be firing this weekend. Yeehaw!
  25. Cluttermagnet

    Cluttermagnet Minister of Fire

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    Dang! I thought I'd bookmarked it, Can't find it now, but it was in a hearth.com thread within the past week or so. If I find it I'll post it. But the chart is pretty easy to read, and the part about 2:1 ratio, as opposed to any 10:1 ratio, you can take to the bank. If you get X BTU's at 20 percent MC, the chart sez you are going to get something on the order of 0.5X BTU's at 40 percent MC.
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