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A carbon negative heater - how a rmh is carbon negative

 
author and steward
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Location: missoula, montana (zone 4)
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Alan Booker started this with

I have been calling it the "carbon negative mass heater system" in my
write-up so far. I call it a "system" because I am specifying everything
starting with the fuel sourcing so that the sum output of the chain is
carbon negative. This requires thinking about how the trees pull carbon
from the air and feed the soil to build soil organic matter. If you
coppice trees for the purpose of growing fuel wood and harvest it
according to a specific protocol designed to maximize carbon
sequestration in the soil, then use a high-efficiency burn chamber
followed by a thermal mass to capture heat before exhaust, the whole
system is highly carbon negative.



I think that there are some really important bits to add here:

  • wood is part of the natural carbon cycle - nothing is pumped up from the ground


  • wood could come from an area that is prone to wildfires - so it was going to burn anyway


  • the need for fuel is so small, a person could just use yard waste and paper/cardboard that would otherwise be hauled away.


  • when your heat comes from wood, you are enticed to plant trees that will provide future heat (preferably coppicing species)


  • Without planting the trees, you are carbon neutral.  

    With planting trees, you are carbon negative.


     
    gardener
    Posts: 5292
    Location: Southern Illinois
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    A thought, or thoughts,

    If your wood comes from a managed woodlot that is either coppiced or pollarded, the root mass stays intact.  This is carbon that was once part of the air but is now a part of a long-lived plant that merely gets a drastic trimming from time to time.  In fact the root mass keeps on growing.  Moreover, carbon is emitted into the soil in the form of exudates to feed soil microbes, thus storing more carbon.  And that long-lived root makes the tree really rebound quickly.

    I can think of any number of ways in which a managed wood lot, and therefore an RMH by extension, are carbon negative in addition to all the ways already mentioned.

    And I can think of more ways further that an RMH is better at CO2 (or equivalent) emissions than any other form of heat, perhaps excluding passive solar (maybe).

    To summarize, I totally believe a properly functioning, well-managed RMH is carbon negative.

    Eric
     
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    Met earthmover his dad and son on the 36 acres to go over placement of roads, 90’ walipini and excess dirt. Heavily wooded with old growth Pinion Pine and Juniper trees the dad asked if we were going to heat with wood, this lead to a lively conversation about rocket mass heaters that they were familiar with. Told them we were leaving the old growth as is, no cutting or clearly of trees opting for growing trees for fuel with litter for composting. The Pinion wouldn’t be good for a rocket mass heater giving its sap content that would be like pouring turpentine in the feed tube leading to incomplete combustion. The Juniper being twisted would be too much work getting it to feed tube size.

    Excellent subject, agree that a RMH is best looked at as a system from fuel sourcing to exhaust that can be very carbon negative.  
     
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    Location: Massachusetts
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    I have a lot of trees -- about 200 of all ages on my 1.4 acre plot.

    If I'm just letting most of the new trees that plant themselves stay and grow, does that count as planting trees?

    If I thin out my excess baby white pines and put them in a compost heap, what does that do, carbon footprint wise?

    If I put in a small RMH and pick up fallen hard wood to burn, where am I in terms of carbon footprint?  I'm not sure how to calculate how much fallen wood I would need to keep my 960 sq foot house that I only heat about 400 sq ft of anyways, at about 45 to 55 degrees through my Western Mass winter, which for me starts in November and ends in March.

     
    Eric Hanson
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    Judy, you ask a complex question so I will try to give you a simplified, though abbreviated answer.

    To start with, I think that fallen branches are perfectly fine to use for heating and to still stay carbon negative.  Those branches would break down anyway just laying on the surface and would emit CO2 as well as the much more powerful methane as they decayed.  The trees they grew from are hopefully still living in which the root mass is still growing and better yet, the trunk and rest of the tree is still healthy.  So simply put, I think fallen wood is fine.

    If the tree itself actually falls over, you may as well utilize it for something before it decays and heat is a perfectly good use.

    Now about deliberately cutting down mature trees to allow younger ones to thrive brings us into more dicey territory and I am not an expert so there may be differing opinions.  My personal thought is that it is OK to cut mature wood IF you are engaging in the process of either coppicing or pollarding.  A coppiced tree is one that will grow up from the root mass after being cut down. As long as the tree is given good time to regrow and the root mass continues to grow, we are still in carbon negative territory.

    A tree that is pollarded is grown, but has a major limb cut periodically after which it is given time to grow another limb back.  The same principle applies as with a coppiced plant.  

    Not all trees respond well to coppicing and pollarding so I would need to know more before passing judgment on your proposed cutting system.

    I am also a little fuzzy about cutting mature trees with many decades of carbon sequestered being cut down so another tree(s) can do the same over decades.

    Further, 1.4 acres sounds like a fairly small amount of land to support sustainable wood burning for heat.  It is good to know that you only have a few hundred square feet to heat, but I don’t know your climate, heating demands or tree species.

    Good to know though that you are considering an RMH.  If you decide to go down this path I would make certain that your house is well insulated and then install the RMH so as to capture as much heat as possible from the fire.  From what I have seen, you may be able to harvest small branches and twigs to use as fuel in which case your 1.4 acres might well produce quite a lot of useable fuel if used carefully and efficiently.

    So there you have one of my long winded answers.  I hope this helps.

    Eric
     
    Eric Hanson
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    I wanted to add this as an addition to my last comment.  I just watched a video that in part covered managed vs unmanaged woodlots.  It was clear from the video, in which two woodlots side by side were compared, that the managed and occasionally cut woodlot had FAR more actual wood than the unmanaged woodlot.

    To be clear, there is quite a bit of skill and knowledge involved in selecting which trees to cut, when to cut them and which trees to let grow.

    I suppose that done properly, a managed woodlot would be a carbon negative land plot, though I would want to know more about how to manage the lot before cutting.  Also, once more, I don’t know how much wood the 1.4 acres of woodlot gives you for your RMH and small house.

    Now if you had a 1.4 acre square with a double row living fence made of Osage Orange, I am sure that you would have plenty of wood to use on a continual basis, but much of what you ask depends on the species and age of your existing woodlot.

    But again, to reiterate, with proper skill, a well managed woodlot is certainly carbon negative.

    Eric
     
    steward
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    What I'd love to see is some long term, deep analysis of the carbon activity in an entire home ecosphere.  Somewhat like Marty Bender's analysis of the carbon action at the Land Institute's Sunshine Farm project:

    https://landinstitute.org/scientific-pub/energy-agriculture-society-insights-sunshine-farm/

    tables:
    https://landinstitute.org/wp-content/uploads/2016/09/EnergySSF_tables1.pdf
     
    gardener
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    Location: yakima valley, central washington, pacific northwest zone 6b
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    One day, not that long ago, Paul sat down with Alan Booker to discuss carbon footprint.  Part 2 of the podcast was just released today!  

    https://permies.com/wiki/225164/Podcast-Carbon-Footprint-Part
     
    "Don't believe every tiny ad you see on the internet. But this one is rock solid." - George Washington
    Rocket Mass Heater Jamboree And Updates
    https://permies.com/t/170234/Rocket-Mass-Heater-Jamboree-Updates
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