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simple question - composting woodchips for heat  RSS feed

 
Tys Sniffen
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Location: Northern California
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I'm going to attempt a little Jean Paine water heater thing, and I have an easy compost question for someone who's paid more attention than I have. (I do a lot of composting already, but not for this, like this)

my neighbor had a BUNCH of brush chipped up, and has no use for the chips. thing is, it's already been 6 months since it was chipped. is it worth it for me to go get a truckload of that, or has the best heat already happened with those piles in the woods?

or, another way to ask the same question: when during a composting process do wood chips give off the most heat?

Tys
 
John Polk
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The heat in a compost pile is relative to the mixture of carbon and nitrogen.
Ideally, a C:N ratio should be around 30:1
If it is too high in N, it will essentially rot.
Too high in C, and it will just sit there with very little action.

Without a source of N, the wood chips (mostly C) will slowly (over a number of years) break down without generating any measurable heat. They are nearly inert without a source of N to feed the critters who begin the composting process.

 
R Scott
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The process does not happen in a set amount of time. It really depends on if all the pieces needed were there. If it was dry or not enough nitrogen or a hundred other things, they probably haven't heated at all yet. If there was plenty of nitrogen and water (like living green trees when chipped) and they had enough air in the pile, then they may be past prime.

Mostly carbon wood chips (large branches or dead wood) take a long time to break down.
 
Tys Sniffen
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yes, I should have qualified - mostly Green trees and bushes, sitting there all summer, in the extremely dry northern California summer.

My intent is to add manure and 'starter' - goop from my waste veggie oil filters.
 
Roberto pokachinni
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One of the differences between Jean Pain's system and what I think you are describing is the shape of the chip itself.

Pain designed his chipper to create a different unit of debris than the standard chipper shredder. The resulting unit of debris is more like a bent up matchstick than the chunk of wood.

From a Mother Earth News article Mar April 1980: "Jean prefers a cutter that produces slivers rather than chips . . . since water penetrates the surface of a long thin fragment more easily than it does blocky chunks. Though the shavings may be as much as an inch long, the ideal thickness is about 1/16 of an inch."

I believe Pain ran his debris through his special shredder twice to achieve this particular size and shape. The reason that he strove to create a debris like this is that the thin shard of wood has a greater external surface area ratio to it's internal surface area. When moisture was added to the piles as they were built, there is that much more biological potential acting on any given micro unit of surface area on a shred, and therefore composting action en masse can take place.

Pain also took special interest in ensuring that smaller wetter herbaceous shrubs and other material with a great deal of green leaves on them were shredded along with his dry dead materials, enough to provide the needed nitrogen, as John P said:

the wood chips
are nearly inert without a source of N to feed the critters who begin the composting process.


The problem is not just nitrogen, but the potential (as described above), for the right amount of nitrogen and water to interact with the carbon source via the right shredded size. Mother Earth News did an article on creating a Jean Pain system but it's first system failed to last very long into the winter after generating an initial burst of heat. The reason was concluded to be the large chips they were using. They experimented further with smaller debris sizes with demonstrable differences in temperature and in the amount of time that the heat was generated.

All these articles are easily searched online. Here's one:
http://www.motherearthnews.com/diy/compost-heater-zmaz80sozraw.aspx
 
Roberto pokachinni
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Mother Earth News was convinced in their experiments that the piles did not have to be as massive as Jean Pain's to do the trick.

Other's have created smaller scale systems from compost:


but this last example on youtube is not wood chips.
 
Roberto pokachinni
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If you have access to a chipper and can run those chips through to shred them a second time, while moistening it, you will probably have greater gains, than if you just try to use those chips straight off. You are going to add nitrogen so this is great, as most of the nitrogen reserves were probably used up trying in vain to compost the chips that are too thick to fully break down. Since you have composting experience, use your intuition about how you would best compost this type of debris.

The piles were likely not that damp and so did not compost too much yet (though they may have been rained on, there is likely a lot of drier material in a pile than you think). I don't know what the size of those piles are and that might make a difference on how much composting has taken place. I don't know what your rainfall or humidity situation is like, so it's not possible to determine what type of breakdown has taken place. Go have a look. Dig a hole in it. Stick your hand deep in the hole. You will still feel some heat if there was some being produced.

Definitely have a hose available to sprinkle the chips as you layer them in your pile. Moisten as you would a compost, and try to consider the amount of moisture and nitrogen that will be needed to combine with the carbon that you have to make real compost.
 
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