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Is burning wood for heat carbon neutral?

Post in 'The Green Room' started by Dune, May 31, 2011.

  1. Dune

    Dune Minister of Fire

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    If one were to burn wood instead of fossil fuels for heat, is this carbon neutral?

    The general gist of the carbon neutral theory is that when fossil fuels are burned, carbon which would have been and remained sequestered is released into the atmosphere, thereby releasing ADDITIONAL carbon. When wood is burned, it only releases the amount of carbon collected during it's lifespan, thereby not increasing the net carbon in the atmosphere.

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  2. Delta-T

    Delta-T Minister of Fire

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    its time scale related...if you cut a mature tree, to reach neutrality, you must grow a mature tree. ~50 years ( i know some tree shorter time,different by region too). This is why there is such a push for grasses and agricultural waste in the pelletized biomass universe...shorter time scale= more carbon neutral and since the root systems in grasses stay alive, they are a sink for carbon,nitrogen and stuff.
  3. semipro

    semipro Minister of Fire

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    I think the answer might be more complex than it seems but I definitely think that burning wood is a better option if you're only considering the carbon cycle. Other considerations are the other pollutants created and impact that occurs when fuel is produced, transported, or used. Both wood and fossil fuels require energy for production and transport and create adverse impacts in many ways. If you're cutting from your own managed land then it seems to me that you're way ahead.

    In general, I think you hit the main point though: its best to leave what's already sequestered alone and then burn wood in a sustainable cycle of sequestration and liberation... or better yet, harvest solar radiation through other means, PV, wind, etc. although these methods are themselves impactive.
  4. dougstove

    dougstove Member

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    This is a complicated question.
    No use of carbon-based energy is ever truly neutral because there are always losses and inefficiencies. The biosphere does have some capacity to buffer our releases, although we are currently outrunning the biosphere uptake capacities.

    More specifically:
    i) How much fossil fuel is spent harvesting and transporting the wood?
    Wood has a low energy density/kg compared to coal or oil, so the energy cost for transport is high. To truck a ton of wood 100km takes the same energy as trucking a ton of coal 100 km. But the coal contains twice as much energy per kg, so the delivered energy is twice as much for the same transport energy.
    At some distance between source and usage, wood is no longer worth transporting. The beauty of Texas or Saudi oil was that the energy cost to harvest and distribute it was very low; Energy Return on Investment was high. Now the good stuff is mostly gone and the problem with Alberta tar sands or deep offshore drilling is a low EROI.

    ii) Is the wood harvested sustainably, so that the land can recapture the CO2 release by regrowing new vegetation? In some areas of maritime Canada the soils are so poor that we are likely on our last stand of trees - if they are cut and removed, trees will not grow back. But we are still generating woodchips like mad and we are not systematically returning the ash nutrients to the source soils.
  5. btuser

    btuser Minister of Fire

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    I'd have to say no. A lot of wood is just going to rot in place, therefor release the carbon anyway so look at it that way. Wood fermenting in a forest stew will produce methane which is a lot worse than CO2.
  6. dougstove

    dougstove Member

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    Production of methane from rotting wood in the forest will vary widely depending upon conditions of temperature and oxygen levels.
    Most decay paths produce predominantly CO2, under most soil conditions.

    But in the short term, methane CH4 is about 23X more potent as a greenhouse gas than is CO2, so carbon for carbon it has a bigger impact.
    Roughly, if the decomposition releases more than about 5% of the carbon in the form of CH4, then a clean burn releasing straight CO2 would have a lower shortterm greenhouse effect.

    But there are active methanotrophs (bacteria that consume methane and release CO2) in most habitats that produce methane, so actual methane releases to the atmosphere are often scrubbed down lower than the initial production rates.
    And most wood burning is not particularly clean, and does not completely convert the wood carbon to CO2.

    Also, wood does not decompose completely and some of the recalcitrant carbon enters long term (thousands of years) storage in the soil.
  7. BrotherBart

    BrotherBart Hearth.com LLC Mid-Atlantic Division Staff Member

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    When the average oak tree is gonna give me three quarters of a cord of firewood, and left laying that tree would take many years to release carbon et. al. into the atmosphere but in a cold month my stove is gonna send the stuff to the sky in four weeks, I don't kid myself that my wood burning is "carbon neutral".
  8. RIDGERUNNER30

    RIDGERUNNER30 Member

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    Like i say by the time these tree hugging hippies and epa gets threw regulating everything, they will tell us that we cannot burn wood no more and they will base there theory on some educated jackass, look this world the good lord created will only last so long, I don't believe we should abuse it, but we should use our natural resources and come up with ways to burn them more cleaner. we for sure don't need to send our money across seas.
  9. woodchip

    woodchip Minister of Fire

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    The main problem I see with wood is not the emissions from the burning, which may well be the same as if the tree had died and then rotted, but the fact that once the tree is down, it is often hauled longish distances and then burned.

    That is where I reckon the carbon emissions kick in ;-)
  10. Adios Pantalones

    Adios Pantalones Minister of Fire

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    The best things we could do for carbon neutrality would be to move to cities in warmer climates. Big compromise, IMO.
  11. Dune

    Dune Minister of Fire

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    A lot of times it's not though. I just had a cord of oak dropped off that was cut less than a mile from my house. This years pine, is from the house across the street, last years was from the house next door to it, and next years is from the house on the other side. All of this wood was headed to the dump if I didn't take it. They are all trees which were cut down anyway, not cut for firewood. The only still standing trees I cut are already dead.
  12. woodchip

    woodchip Minister of Fire

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    Most of my wood is the same, either destined for landfill or just left to rot behind our house in community woodland.

    It's crazy here at times, a tree surgeon down the road who often drops a few bits off often has to pay for suitable disposal of wood, taxed of course.........

    The cynic in me says some types would rather see it go to waste so they can get tax, than see it burned. Madness really ;-)
  13. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Burying wood deep would act as carbon sequestration. Of course, then you may be stuck with a less carbon-neutral heat source anyway.
  14. Dune

    Dune Minister of Fire

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    This is part of my point. Up 45% of the mass of a tree is the root system. Even if it is not entirely sequestered, much of it is, so asuming other trees replace the removed one to continue acting as sinks, some sequestration has ocurred. Soil is composed almost entirely of carbon, not counting the sand or clay base.
  15. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Most soil, including agricultural, is but a few percent carbon total. I'm not sure how you can discount soil and clay (that's like saying- 'chili is made mostly of salt, if you don't count meat, tomatoes, beans, water, and other spices') , but even very loamy soils are not mostly carbon, except in the very top of the layer in the woods.

    Cut down a tree and leave the roots- most of the roots will be lost/converted to a gas as well. Decomposition into humus is not better than 50% efficient.
  16. Dune

    Dune Minister of Fire

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    I say it because compost is almost entirely carbon, and around here, soil is sand or clay mixed with composted vegatation.
  17. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Compost is. Soil is not mostly compost- even when well amended. My garden is mostly compost, but I manage it much more intensely than agricultural land, which accounts for most of the land used for growing (Lawns are not amended so much either).

    The percentage of vegetation that turns into humus during composting is still low. Not all of that matter is carbon, either.
  18. DaveH9

    DaveH9 Member

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    if one can grow as much wood as one uses in a year, then the heat is carbon neutral. Insulation and stove efficiency can help make this happen. By using solar to supplement the wood heat, or wood to supplement solar heat. These new passive solar haus would be easy to heat with less than acre of wood lot, one 8 inch tree a year would do it. If you grew fast growing hybrid popular it would be interesting to see how much land would be needed compared to btus.
  19. GaryGary

    GaryGary Feeling the Heat

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    Well said.

    And, an interesting question -- Just as a rough guess on the question:

    The ref listed below says 5 tons of poplar per acre in the Ukraine (I'm sure we can do better :)

    Taking a 2000 sqft house in a 6000 heating degree day climate (cold), and with R60 ceilings and floors, R30 walls, R4 windows, and 0.3 ACH infiltration, the yearly heat demand is about 39 million BTU, and of this about 17 million is met by internal heat gains (lights, bodies, dogs, ...) leaving 22 million BTU to be met with heating fuel. It could be less than this if some passive solar was used in the house design, but say no solar. Not sure that this home would meet Passive House Institute standards, but its a good efficient home.
    http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

    Could not find a value for heating value of poplar, but aspen is listed as 27 lbs/cf, 2290 lbs per cord, 14.7 million BTU/cord.
    So, with an 80% efficient wood burner, it would take (22/14.7)/0.8 = 1.87 cords, or (1.87)(2290) = 4280 lbs of poplar(aspen) to heat the house.

    With the 5 tons of poplar per acre, this would be less than half an acre -- as a very rough estimate.

    Seems like a good strategy for a pretty close to zero net carbon home.

    Gary


    From: http://www.hemphasis.net/Paper/paper_files/hempvtree.htm
    "In Ukraine, poplar wood grown for pulp produces 5.1 tons/acre/yr, and dry stems of hemp produce 3.24-4.05 tons/acre/yr. This is 4-5 times more than indigenous forests in Ukraine, and approaches the increment of the most productive plantations of fast growing poplars. The Ukrainian Institute of Bast Crops expects hemp to yield an average of 5 ton/acre of dry stems. The cost of transporting hemp pulp, dispersed over larger territories than wood, removal of the ash content, and the lower pulp yield compared to wood pulp make non-wood pulp more expensive. However, the Ukrainian Institute compared the labor costs of growing and harvesting hemp and poplars in 1992 and found the costs were comparable. "

    Heating value for woods: http://www.builditsolar.com/References/woodhvrs.htm
  20. turbocruiser

    turbocruiser Feeling the Heat

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    That was fascinating for me to read through and I think that I understand almost all of it except the 6000 degree day climate. Can you elaborate and explain the math to that figure and also "convert" that to what temperature this 2000 sqft house would be at during the day? Thanks.
  21. jharkin

    jharkin Minister of Fire

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    Is wood carbon neutral? Unless you are cutting with an Axe, bucking with a 2 handed crosscut saw, splitting with a maul, and hauling with a horse team- NO.

    Its is much LOWER carbon than FF however. Assuming you plant a new tree to replace the harvested tree, eventually all that carbon in the wood will be recaptured. Same thing if the tree fell and rotted, it feeds new trees. The carbon running the chainsaw, splitter and trucks is all coming from the Jurassic however :(
  22. Adios Pantalones

    Adios Pantalones Minister of Fire

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    the steel in the axe, saw, and maul were all smelted with non-carbon neutral methods. The handles were turned with power. The horse is eating feed that was fertilized, planted, harvested with fuel.

    It's everywhere!
  23. Hunderliggur

    Hunderliggur Minister of Fire

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    I guess I am OK on the carbon neutral front ;-) I have 44 acres, I can harvest 10 to 20 cords/year according to my forest management plan (long term sustainable), and if I run short, I'll ask the golf course if I can manage the north part of their forest too!. I do use a tractor to harvest the wood and a gas splitter and chain saw, but our house is 100% wind power through the utility (Clean Currents). Maybe I do need that draft horse. [My property is inside the green lines]

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  24. jharkin

    jharkin Minister of Fire

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    Yup.

    And your own sweat equity swinging that axe is powered by the food you eat that is grown from FF based fertilizers and harvested with FF machinery.

    S*(*&^ no matter what we do.
  25. sesmith

    sesmith Member

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    Here's a link to an article in Northern Woodlands Magazine that explains it better than I can. It was in response to a study that made the news by stating that wood burning was not carbon neutral. It comes down to how you measure things, but if the wood is sustainably harvested, the bottom line is yes.

    http://northernwoodlands.org/articles/article/another-view17/

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