Posted by: energymd | December 5, 2008

Heat free (nearly) with a compost furnace

The following is a post created as an adjunct to an educational science unit on alternative energy.   If you desire other specific information please leave a comment.  Thanks,  Marc.


Winters are exceptionally cold here in Wisconsin.  I got tired of trying to feed the insatiable appetite of the three oil burning furnaces that heat my home.  When oil prices started rising several years back, the cost of fuel became prohibitively expensive.  After surveying the available alternatives I decided to capture the excess bacterial heat from a compost pile to heat my home. 

First – the basics:  Mix a big pile of carbon and nitrogen organic materials (shredded brush or brown leaves and green grass for example) in the proper proportion (about 30:1), add water until it has the consistency of a damp sponge (about 45~55% moisture content), keep it aerated so the bacteria can breathe, put some garden hose into the pile and run it into the house where it will connect to a radiator (like the one in your car) then back to the pile.  A pump circulates water through the hose and radiator, and as the pile heats up the water, the water heats up the radiator and a fan moves air through the radiator to transfer the heat into the room!  Voila – nearly free heat!!!!! 

Some logistics:  I live and work on several acres of wooded land, so getting plant material isn’t a big deal.   I use heavy equipment to move the material around, so that helps a lot!  For those of you living on residential lots, using a scaled down version of this technology to preheat hot water is a very practical way to lower your monthly energy bill.          

Some specific data and rationale:  Why compost?  Because as best as I’m aware, it’s among the most practical and efficient processes (some say >97% eff – although I think that’s optimistic) for capturing, storing and recovering solar energy that is immediately available at a reasonable cost.  Published values vary, but typical are compost energetic values of 18-19 MJ/kg or 17,040-18,012 Btu/kg  on dry matter basis, 8~10,000 BTU/LB is frequently cited.  The compost I’m using weighs about 40lbs/ft2, and my design specification requires 750 BTU/ft2.  For the technically curious, compost heats to about 120~130 deg F through the action of mesophillic bacteria initially, at which point thermophillic bacteria take over and heat the pile to about 150~160 deg F for a while at which point the temps drop back to the 120~130 deg F range where the mesophillic bacteria take over again to finish the job of decomposition.  It can be a very complete combustion process, and an examination of my pile reveals white ash remaining as residual matter.  Once the thermophillic bacteria have taken over, you can’t keep your hand under the stream of water circulating through the pile or you will be burned – pretty cool huh?

Here are some pix to click – enjoy! 


  1. Do you have a step by step plan with pictures and descriptions?
    I read a similar story about some old German guy that did the same thing.
    We have 3 huge trees that drop a ton of leaves and would like to do something with them.

    • Hi Terry,

      I don’t have any more detailed information than I’ve provided here as of yet. The system is still in its infancy but if and when I get the process refined to the point where it becomes practical for people to deal with, I’ll likely publish more detailed specification either in this blog or in an E-book as some have requested.

      Thanks, Marc

  2. On a larger scale, Villages could recover compost heat, use it to assist bio-gassing of sewage, yielding fuel gas, fertilizing sludge, and sell the sludge, and compost to farmers to replace the corporately burned out top-soil that threatens American food supplies as we enter the “scarcity age” . the end of the “cheap Oil Age”. The excess heat can be transported to homes, greenhouses, for the people, no corporate profits extracted, no corporate ROI equations applied! A “Communal” effort as in the old “Barn Raising” days of America, neighborly like! A recently lost but precious and very “American” thing!

    • Hi Uncle B,

      I worked on just such a system some years ago. Solids from municipal wastewater were broken down in anaerobic digesters where the methane gas produced was used as fuel to run generators which provided power to run the facility. The excess electricity was sold back to the power company. The resultant digester effluent was sold as fertilizer under the trade name “Milorganite”.


  3. I am in the process of building a large solar greenhouse and wish to use some older design considerations. Mainly Recycled Styrofoams breeds for insulation. I found your site to be very informative and I was wondering if you knew of anyone who has developed the use of Styrofoams breeds used much like the bubble systems that are currently being discussed?
    Looking forward to your reply.

    • Hi Ed,

      I’m not sure what you’re referring to when you reference styrofoam “breeds”, so I can’t answer your question directly. Are you referring to anaerobic digester technology that yeilds greater surface area for bacterial growth through the use of beaded substrate or ???

  4. Prob means beads – I’ve read about a system that uses styro beads blown into windows at night for insulation, vacuumed during day for solar gain.

    “German guy” is likely Jean Pain, a french forester who claimed to heat his house using brush compost (and methane for his truck).

    Would love to know more about this systrm – how far away, temps at pile vs radiator, etc.!


    • Shawn, I’m wondering then if the “bubble systems” that Ed refers to are those which use bubble wrap as an insulating curtain over the glazing similar to the benefit from blowing in the styrofoam beads.

      Jean Pains’ book and videos are now available FREE in the public domain. Links can be found on the builditsolar website. It’s great reading to get up to speed on the basics of composting with wood chips. Thanks Shawn!

  5. Hi : Just wondering what a aeration squirrrelcage blower is, You show a picture of it but I dont think you mentioned it in your description .


    • Hi Tom, Good question! The aeration blower is just another name for a fan that blows air through the compost pile. The air is circulated through the pile by the large blue perforated pvc pipes in such a manner that a little air escapes through each of hundreds of small holes. The holes are sized and distributed in such a way as to meter the correct amount of air through the pile. Marc

  6. what was the air quality like inside the compost area?

    I get 30-40 yards a week of tree service chips delivered to my farm every week — I’ve been considering building a barn with a concrete floor and a tall roof, and putting in 3-5′ of chips as both animal bedding and the primary source of heat for the building.

    I raise pastured pigs, so most of the year the pigs are out on the pasture, but during the winter I’d like to give them more shelter and warmth, and I’m wondering if this isn’t the ticket. Pigs will root around in the compost and turn it, and the heat will be generated right were it’s used — a radiant floor.

    • Hi Bruce,

      The air quality was quite good after the first couple weeks. Initially, it had a bit of an amonia smell from the excess nitrogen in the pile. The pig manure would likely be an excellent source of nitrogen for your pile. There are a number of compost heating systems recently employed to the purpose you intend. One of the most recent systems used a concrete floor with ducts poured in place so that the warm air could be sucked down through the pile and used to transfer the heat to heat pipes which were in contact with a large thermal mass by way of tanks of water. The water was then circulated through heat exchangers to provide heat to the areas required.

      • Hello there.
        you said “There are a number of compost heating systems “. can u paste me a link for their technical description? i have read your article and i have a few other questions about your method, such as size of pile, size of the heated building, etc. i dont know if u can see my e-mail, if u cant, please let me know and i can write it here 🙂 thank you a lot 🙂

      • Hi jakub,
        I appreciate your interest in my composting system, but I regret that there is no substitute for due dilligence. Providing you with more specific information about my design parameters won’t help you design your system. These systems are site specific and require that you do your own math to satisfy the requirements of your intended use. As for your request to send you links, please use the links posted on this web page, the information you seek is likely posted therein. Take care, Marc

  7. Ive been reading up hot compost,and i’d like same feed back.Im thinking about using horse manure as a base & wood chips then lay the hose over that then some damp green grass & brown leafs.Cover it with and old swimming pool.I’ll have it about 10 feet from the house.Im not sure what size of pump to put on it[thought about the swimming pool pump] I could use some advice on this.Thanks

    • Hi Rick,

      The design of these systems is site and situation specific. As I frequently advise people who ask similar questions, as an automation engineer, I am available for hire as either a consultant or to design your system outright. Generally speaking, just make sure that whatever you do, that you allow air to circulate through your pile (ie don’t cover the pile with a close fitting tarp or swimming pool cover). If you do, the pile will generate methane gas, not much heat, and become an explosion hazard since the gas will be contained. Thanks for the question! Marc

  8. Hi, I’d be interested in knowing the amount of energy expended in the collection of materials, shredding, moving into a pile, forced aeration, pumping the water around, blowing the heat around and dis-assembling the heap when ‘done’, compared to the energy you recieve into the house. Although I love the sound of your process, it sounds quite energy intensive with all the machinery used. It may not be as ‘nearly free’ as you think.

    I’ve described a simple and small scale system that ‘ordinary householders’ could try, to make hot hand-wash water, in paragraph six of

    Also, In your description of the process, you say that you are left with a ‘white ash’ after the almost complete combustion in the compost pile. I would question whether you are experiencing ‘combustion’ and I don’t think this is ash. I’ve had similar layers of material in some of my shredded wood-heavy compost piles, and it’s (I think!) the mycelium of a fungus. I think it merits more investigation.

    I’m looking forward to reading more of this website, thanks to Rex my facebook friend for the link!
    John Cossham, York, UK

    • Hi John,

      Interesting “fodder” for thought yours 🙂 The process


      in fact as nearly free as I think. Consider that less than ten gallons of diesel fuel was consumed by the combined utilization of my mini-excavator and bobcat for material handling. Double the figure if you like, to allow for moving the material off site to be used as fertilizer once decomposition is complete. The aeration blower consumption is negligable since it only runs four times a day for 15 minutes at each interval. Finally, the pumping costs are also miniscule amounting to no more than ten dollars a month to run. Considering that my initial pile provided a +40 degree temperature differential to ambient on a sustained basis in my house; for months, it’s intuitively obvious to the casual observer that the system is operating profitably in this application. You raise a good point however, in so far as assembling and maintaining the pile is somewhat labor intensive, but then I don’t charge myself for my time :)~ To be candid, it probably takes me the better part of a week to dismantle and reassemble the pile, but I’m working on bringing that number way down through current redesigns of my heat exchange approach.

      As for your supposition that what I am observing is in fact mycelium, while an interesting speculation on your part, it is I’m afraid inaccurate. I’m familiar with mycelium and that to which I refer is most definately not of that origin. I believe that the pockets of ash occur where the nitrogen concentration and aeration circulation is the highest and where the greatest surface area is available for decomposition of the wood chips (ie somewhat like course sawdust in its initial state). Jean pain refined his approach to include the processing of his wood chips to this – finer state of matter prior to being inserted into his pile. My experimental results are consistent with his findings. The white ash is available in pockets of such quantity that you can scoop up handfuls of it and for all outward appearances is indistinguishable to that which you’d find at the bottom of a fire pit. Numerous university and independent studies have been conducted on hot composting, yielding complete decomposition/combustion in as little as two weeks with 70% reductions in matter. Thanks for your excellent comments and questions! Marc

  9. Just found this is, I think, your first post. Good luck with this blog. John

    • Thanks so much! Marc

  10. I’m always looking for new informations in the world wide web about this matter. Thanks!

    • If you find anything of particular interest, I encourage you to either repost here or provide a link – thanks! Marc

  11. Hi Marc:

    Just found your blog. We have been trying to do something similar for a couple of years at our farm in NY. I have just started communicatin with Rob at

    It seems all of us are trying to accomplish the same thing and running into the same problems. You look like you are further along with your stuff, though I have done alot of experimentation to date.
    Perhaps there is some way that we can work together here. Each doing some seperate research. I have just made the suggestion to Rob.
    We have blogged for a long time at New Farm, and just started our own blog

    My e-mail is

    Best hopes,


    Live Simply So Others Can Simply Live

    • Thanks for the note Ed! I had initially hoped that this blog might be a forum for such collaboration. Regardless, I do hope that those who are interested and have something to contribute will contact you for possible collaboration. To that end I’ve retained your email in this comment. All the best, Marc

  12. Just curious about how much bio-mass you think you used, as in what were the approximate dimensions? Also, how big of an area were you able to heat? You talked about getting the carbon/nitrogen proportions correct, do you think that just happens naturally? I’ve read a little of the Jean Pain stuff and he didn’t seem to over worry about the mix, just used shredded scrub. Anyway thanks for posting this work! We are indebted to you. -Jeff

    • Hi Jeff – great questions!

      My compost pile was about 32’L x 12’W x 6’H give or take (I’m going from memory here but it’s close). I was heating an area of about 800 ft2. I definately do NOT think that the Carbon to Nitrogen ratio happens naturally. I calculated the amount of Nitrogen required based upon the mass of the Carbon material. Getting an even distribution of the Nitrogen throughout the pile is one of the areas that requires greater attention. Conventionally, the materials are mixed when the pile is created and nature is left to take its course with some mechanical assistance by way of turning the pile and aeration. As best I am aware, Pain built up his piles in layers alternating Carbon and Nitrogen materials interleaved. Thanks again for the excellent questions! Marc

  13. […] Imagen: Energymd – Practical Alternative Energy […]

    This link was left here in the comments section, and I’m leaving it situ. I used the google translation function and found some really good information there… take a look! Marc

  14. Can you take some of your “white ash” and put into some water and check the pH. If it’s really an ash it will be basic. Great project!!

  15. Hey Marc,
    Awesome project !!
    I a going to build a system this summer/ late summer. I am wanting to heat my greenhouse with it. Was originally planning on using the hot water in a radiant heat floor system in the greenhouse. The picture of your air handler/heat exchanger, is the air that is blown out warm enough to heat a room ?
    Also, was wondering how the size of your compost pile/ temp of water and how often you need to rebuild the pile ?? Any info on these questions would be great !
    Jeff Newton, Iowa

    • Hi Jeff,

      The air is hot enough to heat a room! Please read the various Q&A in this comments section as well as the full body of text, and I think you’ll find your questions will be answered. Best of luck with your greenhouse project. It’s a very popular use of the technology. For more information to your specific application, check out the new alchemy workshop. Thanks for your question!

  16. Marc,
    How many gallons per hour were you circulating through your system?


    • Hi Bob,

      Since it’s a “demand” system there’s no simple answer to that question other than to say that it has a max sustained flow rate of 180 GPH. The pile would be stone cold if I tried to run the pump at a 100% duty cycle to maintain that. I think what you’d like to know is that the system was designed to cycle on/0ff every 15 minutes to meet the heating demand during a median demand day. At the end of the day, it doesn’t really matter what flow rates I’m using, because there are too many other variables involved for you or anyone to use my operational parameters as a baseline. For example, the size of my heat exchangers both in the pile and the water to air unit that scrubs off the heat into the house, the temp differential between the pile and ambient, the temp differential between my heated space and ambient, the length of run to the house and extent of insulation for that run as well as how well my heated space is insulated. These are just a few of the factors that must be considered when engineering these systems. If you’re seriously considering construction of such a system, you can’t just clone what someone else has done, you have to do your homework or you’ll be greatly disappointed in the result. It isn’t just a matter of proportion either. You can’t for example say that since I’m heating Xft3 that you can just double the size of your system to accomodate 2Xft3 – it’s just not that simple. I spent several years researching and designing my process so as to do all I could to ensure an acceptable result. My advice to anyone wanting to pursue this is to either do the math or hire someone who will – I’m sorry to say that there are no shortcuts.
      Best regards,


      • Thanks, Marc. I’m trying to get a handle on how much flow could be accomplished before endangering the pile from cooling down too far. It’s an issue I’ve never seen addressed anywhere. Obviously, as you mentioned, the flow rate is but one of many factors to consider.
        Like Jeff, I’m looking at biomass for greenhouse heat.

      • Bob, One way to approach the problem would be to place one or more temperature sensors inside your pile in conjunction with a temperautre controller or thermostat and use the relay output from either of those as an interlock with your pump call to run signal. The logic of the system being that at some preset low level temperaure, the pump is disabled until the pile temperature rises above a safe level. Such sensors and controllers are so inexpensive in this day and age, it would be fairly trivial to implement. The temperature levels you’re looking to exceed would be those necessary for the survival of the type of organisms you’re trying to culture (obviously). You would also want to consider the depth of your sensors in the pile and their proximity to your heat exchanger structure (if any) in the pile. For your application, you may find that you wouldn’t need a pump at all if you integrated the pile into your greenhouse floor for example. Possibly you could blow air through pipes in the pile to not only aerate the pile but to circulate the excess heat through the greenhouse as well. A nice feature of that approach would be the circulation of CO2 throughout the building. Good Luck!


  17. Hi Mark,

    Your compost heating project is facinatng. I am wanting to heat our pool and saw somewhere that one can do this by obtaining heat from compost? Could you advise please? We are in the north east cost of South Africa and just wnat the chill off the water in winter.

    Many thanks


    • Hi Janet, What you propose is certainly do-able and might be worthwhile if you have an ample natural source of carbon and nitrogen material close by. My immediate reaction is that you would likely be better served by investigating a passive solar solution. Good luck! Marc

  18. All I can say is “Damn custom.”

  19. Hi,
    Your forum is very interesting. I have read and watched on youtube lots of stuff about compost heat. One idea is to use alcohol instead of water or antifreeze in the heat exchange. Its organic. It has a lower freezing point, and it boils just above the temp of your heating tubes, so you could use it for condensing and releasing heat. And hey, if the compost ever dies, you could break open a pipe and get warm that way.

  20. Something else comes to mind about his heat exchange idea. Why don’t you build yourself a huge concrete platform on a small hill. Then under that platform, a “cave” where you could insert things up into the compost pile from below. So for instance you construct the insulated heat carrying pipes under the ground, to your “cave”, and there attached to a big needle made from PVC or something strong. Then on top of the platform build your large compost pile. When the pile heats up you insert the needle by cranking it up. Inside the needle you have a closed heat exchange loop, aeriation holes with pumped air, and some kind of temperture probe for feedback. After the pipe cools off, you retract the needle, and then your can just backup a pickup truck up to the edge of the hill (where the cave door is) and go up above and push the dead compost heap into the bed of the truck for transport. This leaves you with an empty platform for the next heap.
    Anyways, the needle could have all sorts of efficent designs to interact with the pile from the inside, but its handier that you can retract it back into the platform so that you can bulldoze the top in between batches.
    Just a suggestion. 🙂

    • Hi Thomas,

      Thanks for your comments! The system you describe re: tunnel et al is very similar to that of systems currently in use for cattle manure composting/remediation. They use heat pipes to extract and transfer heat from water vapor passing up through the compost pile where the heat is conducted into a water tank for use as facility heat or hot water supplement etc. Your point of view regarding easier mechanical handling of the composted material with such a system is imho exactly on point to the focus of where I believe these systems all need to be improved. The U.S. Navy also conducted a study of the use of heat pipes inserted into compost piles from various angles and configurations with interesting results. I’ve been working on a method of direct heat transfer from the compost to process fluid which is still under investigation and so I’m unable to comment further about it at this time.

  21. Wonderfull method for heating & use of materials. Our system, based on Jean Pains book, will resemble yours in many ways except it will be used in the very remote forested acreage where we live (soon) & not require any transport of materials other than from inside of our acreage, to our home, on-site.
    You should produce an E-book better describing the building process & ‘how’ it functions. I bet it would proof a worthy venture!

    • Hi Russell,

      Thanks for your kind support. As Thomas in his comments alludes, the Pain heat exchange method is quite labor intensive, as is mine. If I had sufficient space and funds, I would definately construct a well insulated shed to house the pile, likely with large doors at either end to allow a bobcat or loader etc to handle the material and take the heat from the ambient environment in the shed. If the shed were attached to your home, you could circulate the filtered air directly into your house through vents in the wall or some such similar arrangement.

      • I liked your project a lot. I remember reading TMEN articles about Pain and his setup. I lived in the U.P. of MI and have forty acres of maple trees and wonder if I can come up with a vacuum system to suck up the leaves into a wagon/trailer box and take to a small building as you just described. My land is forested rolling hills. In regards to the nitrogen. I understand that green material and/or manure is good for that. Could one use a macerating pump to grind up the green material and mix with water then inject into the pile as needed (based on ?, pile temp maybe).

      • Hi Bill, macerating the organic matter and handling it as a slurry is a great idea! This sort of material handling lends itself well to use in a plug digester or similar. If you proceed with construction of such a system, please drop us a note to fill us in on your system configuration and results. In the mean time, thanks for the note, Marc

  22. Good post, adding it to my blog now, thanks. 🙂

  23. Wow, truly great info. How can I find your subscription?

    Kate Trider

  24. please tell me how long does the organic matter last? I want to do this to heat the pool so I need to obtain more information.
    Thank you

    • Hi Analugoetschel,
      Pool heating is an excellent use for this process (imho – lol). How long the pile generates useful heat is dependent upon the materials used, the Carbon to Nitrogen proportion , the availability of nutrients, moisture and ambient temperature. So what I’m saying is, that your mileage WILL vary. My pile “lasted” about 1 year inclusive of a dormant period lasting several months while I didn’t turn the pile over. Like you, I was interested to find out how long it would produce useful heat without any mechanical intervention. Good luck with your project and feel free to post your results here so that others might benefit from what you learn! Thanks, Marc

      • Hi marc,
        I have reviewed your wordpress site with great interest and would like to ask for some costs for design services. I am located in spain, so site visits not likely but can you please contact me via email or skype terrafirmaproyectos so we chat further,

        Kind Regards


      • Hi Frank,

        Thanks for your inquiry. Commercial engineering services are currently offered at $100/hr. A significant discount is offered for consulting and engineering services to individuals involved in modest residential type composting activities in an effort to promote interest and acceptance of this eco-friendly form of energy production.


  25. […] Heat free (nearly) with a compost furnace… […]

  26. I also think that burning wood and making coal actually makes fume inside the house. And we all inhale this thing every day in winter time. I certainly would go for another solution, great article on how to do it.

  27. Greetings Marc!

    Finding sites like yours really encourages & tickles me. Perhaps you would share a bit of advice, now that you have about 3 years experience with this. Thanks for writing of your on-going research, experimentation, and implementation in this important area. Sadly, folks normally think the basic physics of simple applied technologies like this as complicated, expensive gadgets that only might work for those with much “luck”. They believed the lies they were told. Luck doesn’t exist. I’m currently building a similar system for space heat for my house this winter. So far, the mound of “brown” is about 13′ x 15′ x 7′, with enough on-hand to make it about 8′ or 9′ tall.
    I need to know, sir:
    – Did garden hose work well as your heat exchanger, or do you suggest something else?
    – Did you run multiple circuits? Or only one with 3 parallel legs?
    – Did the hose & washers stand the heat & pressure without leaks?
    – What would/will/have you do differently to improve performance?
    Thanks for sharing,
    Cmdr. Ron

    • Hi Ron,

      No, there’s no “luck” involved, nor is composting a “black art”. That said, there is a certain amount of engineering effort required to correctly size the materials and components necessary to effect the desired outcome. If you just want to produce dirt, anyone can do it without too much thought, but if you intend to extract heat from the pile, a balance needs to be maintained such that you don’t extract so much heat as to kill off the bacterial culture that you’re trying to support while still providing sufficient excess heat to drive your process requirements. You also need to calculate things like heat losses, surface area, flow rates and size the pile and heat exchangers accordingly or you won’t get the desired result.

      To address your questions, the cheapo garden hose I used worked very well but won’t hold up long term. If you want a longer term solution you might try high temp pex tubing (the red stuff). As to the number of circuits of hose that I ran to extract heat from the pile, I used 3, but it’s really rather meaningless, as those requirements are totally determined by the geometry of your pile, the temperature of operation, the pumping flow rates and ultimately, the number of BTU’s you intend to extract in a given amount of time from a given area of composting material. Heat will travel though the pile albeit slowly (temperature is a relatively slow process), so if your demand isn’t too great you can get by with fewer heating loops and longer recovery times. I experienced no leaks with my hose, but the hose tends to harden (as expected) from the heating cycles. I purchased 600 feet of garden hose from a HOBO (discount) store here “dirt” cheap. I would recommend someone do the same while experimenting until they arrive at a permanent configuration.

      As to what I might do differently, my short answer is that I wouldn’t bother with the aeration system. Contrary to some of the information being published on the web, my experience is that there is no substitute for mechanical agitation. Given that requirement, I would choose to turn over the pile at shorter intervals instead. The core issue is that the already digested material (newly created soil) clings to the feedstock in such a manner that it’s not available as a food source for the bacteria.

      I hope this was useful to you and others reading this blog. For what it’s worth, my initial impression of what you’re proposing is that unless you intend to heat a very small area (say 1400 cubic feet?) your pile is most likely grossly undersized for your stated purpose.

      Thanks again for your interest, Marc

  28. Wondering about the brand and supplier of the recirculating pump. Can you tell me where you purchased it and whether it is a “hot water” recirculating pump.

    • Hi Steven, My recirc pump is nothing special. It was just a chemical feed pump that happened to have the flow capacity that I needed. I have since acquired a number of NOS recirc pumps which are well suited to the task. If you’re interested in purchasing one (or several), let me know and I’ll send you the particulars of what I have in stock and you can decide if they’ll meet your requirements. Or in the alternative, send me your flow and pressure requirements as well as your system voltage and I’ll let you know what I have that will meet your needs. Thanks, Marc

      • I’ve built a compost heating system and need info on sizing the correct hot water pump for it. My system has about 650 feet of 3/4 inch black poly pipe and about 50 feet of 1/2 inch braided clear flex plastic pipe. About 20 gallons of water and about 6 feet head in my closed system.

      • Hi Bill,

        The short answer is that I can sell you a commercial grade pump of excess capacity that would most likely do the job for you.

        The longer answer is that to determine your pump size with any real degree of precision, would require significant engineering effort. The operating parmeters of your system need to be clearly defined beyond just the elevation change of your plumbing. You (or someone) would need to calculate the expected btu’s that you anticipate will be extracted from your system to correctly size the heat exchanger(s) and flow rates required. Also, you have to figure out what the head losses are due to friction for pumping a given quantity of liquid through a hose at your specified length and i.d, at a given flow rate and factor that in. What I’m trying to say is that the amount of heat you’ll extract from your system will in part be a function of how much water you pump through it in a given amount of time. If your pump is too small and your pile is too large, the water will be hotter than you might want (unlikely). If the flow rate is too high for the size of your pile, the water will be too cold to be useful for space heating. You can (and should) use a valve to regulate the flow rate through the pump if necessary. All the information you need to figure your btu capacity and flow rates and pressures are easily found on the web, as there are calculators available online to help you figure out what you need. If you want to just buy a pump and try it, I’ll be happy to sell you something to get you started.

        All the best,


  29. Hi Mark and a healthy, happy new year to ya!
    Thanks for providing this great site. It very generous of you.
    We are located in southwestern Vermont and into the third year of our initiative of providing “Energy From Farming”. This is the first year that we’ve worked composting into our energy production menu. We’re following the Jean Pain formula in so much as we are using just wood shavings of a certain dimension for our composting feedstock.
    I was surprised to read in one of your comments that you felt Jean Pain used a mix of materials when constructing his piles. I’m curious why you believe that, as I’ve never read any reference indicating he used anything other than
    shredded wood. Our own experiments indicate that, when the pile is properly aerated, the bacteria have all of the nitrogen and oxygen they need. On piles the size we are working with, mechanical agitation on a regular basis would be impractical.
    We are adding water to our air flow in an attempt to maintain the moisture level in our pile. You show a photo of hydration hoses, so I assume you are trying to do the same. Are you using a slow continuous drip approach or are you periodically just adding water at a know rate? Are you making any attempt to recover water that may drain through the pile?
    You’re offering sound advice to others when you say that each project must be done on a custom basis predicated on the needs and characteristics of each end use. Keep up the good work and again, thanks for sharing.

    Be well.

    Larry Johnson

    • HI Larry,

      In answer to your question about where I got the information that Pain was using nitrogen as a feedstock other than that in the air, truthfully I no longer recall. It was several years ago now that I did all that research and it would take way too much time for me to try to dig that up – sorry.

      As regards my drip irrigation system, I tried both methods both slow continuous and periodic on various duty cycles. The hoses you see are the type that spray a mist of water from many small orifices along the length of the hose. Since most of the hoses were buried in the pile it amounted to drip irrigation anyway. The upshot is that opening the valves to hoses at 12hr intervals twice a day for 15 minutes at each interval worked out the best. There was no need to catch the runoff although I had provided for it with a huge tarp underneath the pile raised up to form a catch pan. Slowing the rate of hydration as I did allowed the chips to absorb the moisture. The flow of water would allow the nitrogen pellets to disolve releasing the nitrogen into and throughout the pile.

      Whether Pain used supplemental nitrogen or not, I determined (empirically) that once the nitrogen was used up from the fertilizer, thermophillic activity ceased. Agitating the pile didn’t help. Adding additional fertilzer did. The response was nearly immediate (about 3 to 4 days as I recall). My pile was fairly large as you can see and compaction became a real issue as the composted material made the pile increasingly dense toward the botttom. Since my aeration tubes were located under the pile this had obvious undesired consequences. Regardless, very early on I found that my aeration system was wholly inadequate for the intended purpose and ceased to bother with it after several months. It made no discernable diffence in output whether I ran it or not. It would have required considerable flow and pressure to provide an effect of pnuematically agitating the pile which is what I ultimately determined was the biggest problem with this configuration. The need for mechanical agitation is so great because it is necessary to slough off the digested material from the wood chips so as to expose fresh carbon feedstock to the nitrogen rich environment. It’s fairly clear that the reason Pain uses the profile he does is to circumvent that problem. I’m intrigued by the fact that you are able to sustain mesophillic and thermophillic activity without the use of a nitrogen feedstock other than atmospheric air, despite the fact that it’s 78% nitrogen rich. I suppose if you can aerate the pile sufficiently well, it makes sense that you could.

      For what it’s worth, I realized that unless you have an ongoing agricultural concern or other continuous need to handle the feedstock anyway, it’s too labor intensive a method to be practical on a scale necessary to heat ones home. Even with my bobcat, it takes quite a while to move all that material around (twice) and considerable diesel fuel burned only to heat a couple rooms in my house for several months. If I had a farm – especially a dairy farm, I’d sustain the operation without question. Part of the appeal was that I could get the wood chips delivered to my house for free from the local electric company subcontractors. I had purchased a large vermeer chipper to rechip them to more nearly mimic Pains dimensions, but there is just too much dirt in the feedstock and too much labor involved in rechipping to have made that practical. So, in the end I decided that burning them in a furnace with secondary combustion was the way to go and I was quite happy and warm with the results this winter. 🙂

      Thank-you for your comments,


  30. quisiera saber como puedo utilizar el compostaje para producir electricidad o mejor para almacenarla en una pila de bateria de carro gracias

    • I don’t know how to turn compost into electricity, but you “could” convert the heat by pumping the heated water into a vacuum chamber where it would turn to steam, and use the steam to drive a turbine which in turn would spin a generator to provide electricity. You could use a turbocharger off a car to do this but I have no idea how long that would last nor am I recommending that you do so.

  31. I’m not convinced the steam created by warm water being fed into a low pressure chamber would be any good for driving a turbine. Turbines are, in my experience, always powered by something under pressure… steam, water, even a strong breeze!

    One way of converting the warmth from working compost into a bit of electricity might be a peltier device, where a temperature difference between each side of the chip causes electrons to flow. I have a peltier device on my woodstove, a fan called an ‘ecofan’ which uses the heat from the top of the stove to warm the base of the chip, the flow of air caused by the spinning fan to pull cool air through the top of the device to cool the top of the chip. The temperature difference is probably in excess of 100 Celsius, but other types of peltier chips might work with the lower temperatures in a compost-based system.

  32. Marc, for turning over the compost and aeration, what do you think about a large scale drum tumbler composter with a few hundred feet of pipe circulating inside? By large scale, I mean the size of a milk tanker. Here’s a mock up. As you can probably tell, I’m not a scientist but this idea of heat capture from compost fascinates me.

    • Hi Michael,

      There are similar systems (albeit smaller) published on the web for review. I’ve spent a bit of time exploring similar configurations. FWIW, my incarnations were essentially configured as plug digesters incorporating insulated water jackets or internal spray recovery and heat exchange systems. The down side of such methods would be the energy required to rotate the tumbler since we’re talking about moving a mass of compost likely weighing many thousands of pounds. Still, if I had time and funding to pursue such an approach, it would be interesting to run the numbers and determine the probable efficiency of such a system. Please report back with your progress. Thanks, Marc

  33. You could definitely see your enthusiasm within the work you write. The world hopes for more passionate writers like you who aren’t afraid to mention how they believe. Always follow your heart.

  34. I have been doing some research on utilizing an insulated chimney to create adequate draw of fresh air through a large pile. A well insulated chimney on top of the pile allows me to cover 70% to 80% of the upper portion of the pile, leaving only the widest bottom portion uncovered to allow for air to travel into the pile. The hot air going up the chimney draws fresh air into the pile from the uncovered base. Covering the upper 3/4ths of the pile traps a significant portion of the moisture in the pile, helping to prevent it from drying out too quickly.
    Many of the principles are the same for when burning wood. A chimney is necessary to create draft to provide a steady supply of oxygen to the burning fuel. An insulated chimney significantly increases the amount of draft by creating a greater differential in temperatures between the air outside the chimney, and that within. In other words, the hotter the air, and the longer it stays hot, the more draft that will be created. In the long term it is far less expensive to build a chimney than to power a fan. Also, solar heating can be incorporated to further increase the amount of draft created during certain hours.
    I would love to hear your comments/thoughts.

    • Hi Ken,

      Thanks for your comments. Your idea is most clever! From a practical standpoint, there are numerous logistical problems with your method, but for the sake of brevity I’ll address only one – mass density. You’re dealing with a damp fairly dense mass that tends to mat together and clog air passages. This makes it difficult to aerate the pile without sufficient pressure differential which I’m doubtful that a chimney of any practical height would provide. In my experiments, my aeration system proved insufficient for the task due to lack of head pressure. I was moving a sufficient quantity of air but at insufficient pressure such that the air would take the path of least resistance through the pile which was usually near the edges. My conclusion was therefore that either compressed air or a MUCH larger fan would be required if one were to follow my approach to mechanical agitation of the pile by way of aeration. I hope you’ll continue your research and keep “plugging” away at it! Keep up the good work.


  35. Hello Marc.
    Nie znam angielskiego dlatego użyję tłumacza google. Mieszkam tutaj .E 15.54684st/N 54,00874st. Zbudowałem układ =rury PE 32 ,100m. ,pompa cyrkulacyjna,grzejniki 2000W. Ogrzewam 100m. sześciennych.
    Stos kompostowy z wymiennym rdzeniem 1 m sześcienny .Wymiana rdzenia raz na 14 dni ….obornik koński.
    Nie zrozumiałem dobrze, kilku rzeczy .
    Czy użyłeś jako dodatkowego azotu -nawozu sztucznego ?
    Nie / Tak … a jeśli tak to ile ?
    Google- insulation blanket …tłumaczy jako koc , pled ,kapa -jaki to materiał ?
    i….może trochę więcej o venttillatio manifold = czy te rury są perforowane ? i mają wymuszony wentylatorem ruch powietrza ?
    I najważniejsze !!!
    Dlaczego używasz powietrza do ogrzewania , zamiast grzejników płytowych ,grzejników ?
    Proszę w odpowiedzi – jeśli użyjesz terminu technicznego ,użyj drugiego terminu równoznacznego .
    Nie odrobiłem lekcji z angielskiego.

    Hello Marc.
    I do not know English so I use google translator. I live here. 15.54684st E / 54.00874 ° N I built a system = PE 32, 100. , the circulation pump, radiator 2000W. Heating 100m. cubic.
    Pile of compost with replaceable core 1 meter cubic. Replacing core once every 14 days …. horse manure.
    I did not understand well, a few things.
    Did you use as an additional nitrogen-fertilizer?
    No / Yes … and if so how much?
    Google-insulation blanket … translates as a blanket, blanket, cover-what is the material?
    and … maybe a little bit more about venttillatio manifold = if these pipes are perforated? and have forced air circulation fan?
    And the most important!
      Why do you use to heat the air, instead of radiators, heaters?
    Please to answer – if you use a technical term, use the second term synonymous.
    No homework in English.

    • Hi,

      1) Yes, I used nitrogen fertilizer due to the unavailability of manure. Since you’re using horse manure, you likely won’t need it.

      2) The blanket is comprised of fiberglass insulation covered with rigid foam insulation.

      3) Yes, the pipes are perforated for use with a forced draft fan. Your application won’t likely benefit much from it since you’re turning your pile over every 14 days anyway.

      4) I think you may misunderstand my system somewhat. My pile does in fact heat water that circulates through a radiator. A fan helps to exchange the heat from the radiator into the air in my home to make the heat transfer more efficient – much like your car heater.

      I hope this helps,


    • Although having rigid foam on top of the fiber glass will protect it from rain, it will likely still get saturated from moisture trying to evaporate from the pile. I would place a thin layer of plastic under the fiberglass, or it will serve no purpose. Of course you have to allow your pile to breath too. Air forced in needs an exit point.

      • I experienced no problems with the insulation becoming saturated with water. Thank-you for the suggestion. Marc

  36. Very interesting, mostly because is makes sense. I live in rural Mid Western Ontario, with very cold winters. I have a heat pump, but only efficient to about -15C. I would like your opinion on surrounding the heat pump with compost barrels. When the fan comes on, would the pump gather passive heat from the compost?


    • HI David. I’m assuming you have an air to air heatpump similar to an air conditioning system operating in reverse (as opposed to a water to air system which uses either ground water or an in ground heat loop of pipe to circulate water as a heat source). That being the case, you “could” enclose your compost heap in an insulated envelope and draw the warm air into your heat pump in that manner. If you compost pile is large enough to meet your heating demands, it should work. I would like to advise you (and others contemplating such technology) that it is almost certainly more efficient to use water as a heat exchange medium rather than air. Good luck with your project!

  37. Very interesting blog and discussions indeed. One question that keeps coming when I read all the information and Pain’s model and experiment. This composting method would last about 25-45 days max until materials and decomposed. Should we change the materials? I did not see Jean Pain do this! If so, then it would be very cumbersome to change the materials while maintaining the heat exchanger from the pile, right?

    Thank you for the help

    • Hi Fadi, you’ve got to the “core of the matter” for sure. The pile needs to be mechanically turned periodically to expose undigested material to the wood munching bacteria and to mix the carbon and nitrogen bearing elements. I tried to circumvent the need for mechanical agitation by injecting forced air through the pile. My tests determined that a compressed air source would be required to do a proper job of it rather than just passing air through the pile, as forceful agitation of the feed stock IS required. As a practical matter, I would think that routing the compressed air through series of outlets beneath the pile – in a sequential manner would be the most practical approach so as to keep the CFM requirements to a manageable level. If you do a bit of research on the web, you’ll find commercial designs being employed which use retractable heat pipes that pierce the pile to allow for material handling. Similar methodology could be used with retractable compressed air pipes. Alternately, the pile could be arranged on a downhill grade in a manner similar to some plug digesters which self feed material through the system by gravity as it decomposes. Another option might be to use one or more augers to move the material through a digester. Thanks for your comments! Marc

      • Guys,
        Many of you have, somehow, missed a critical portion that I saw and tested. Even using rapidly deteriorating materials (like grass and food scraps), composting usually requires months. During power line right of way maintenance, tree trimmers dump truckloads of shredded wood at least once every day. They happily brought 3 (of the 14 requested) loads to me. Two loads were dumped where I could shift them into 1 huge mound, nearly as big as Pain’s. It was over 9′ tall and roughly 13’x15′ long, plus 2 pointed ends to use for composting daily scraps. I occasionally watered it, mostly during dry spells. The size was far more than is easily turned with only a pitchfork. Pain’s piles had water piping to transfer heat, which eliminated turning piles to aide aeration, yet they worked. Sadly, mine were not piped. After about a year, the pile had visibly shrunk (from compression). Investigation revealed the core was nearly dry and compost activity had slowed dramatically – probably lack of adequate turning. The severe material disturbance admitted much-needed air, and I changed the top to more saucer-shaped and re-wetted the pile while turning. This appeared to greatly accelerate pile activity. The top now captured rain (that previously over-flowed down the side) so it could soak through the pile. Using the shreds and compost late in the experiment, I saw the bottom 18″ to 24″ of the center was still nearly as fresh as when the pile was formed. Much smaller by the 3rd year, turning the mound was far easier. I used most of the pile in gardening, both marvellous compost and shreds for mulch. Much was learned in this very successful experience, but not why Pain’s piles worked so well producing heat without periodic turning.

      • Thank you very much for the reply and detailed information. I understand the need for moving the pile, but as Ronald’s important case and comments, I have the same question about Pain’s case. None of the literature that I read about Pain’s case mentions turning the compost pile. Were there any missing information about this case, or is it something that I do not see?! In the case of Pain’s pile, it is almost impossible to turn it without removing the pipes first.

        All the best

  38. One of the ideas I have is to use the aeration system that you described in your blog and add liquid forms of nitrogen (diluted urea or urine for example)

    What do you think?

  39. To get air to the pile , would putting drip irrigation tubing in the pile , (netafim with emmitters) then hooking to a small compressor with a 10 psi regulator ( netafim brand) a bonus would be that to increase the moisture content you could unhook the comperssor and hook it to water supply and let it run for a couple hours . I am a irrigation contractor . I was moving some mulch and woodchips mix and noticed how hot it was , I am going to play around and try to heat a 20 by 20 workshop I have . And use up some stuff i have laying around .

    • Interesting idea. Please keep us posted on the results

  40. Hi Marc
    We have this kind of system at our place built by the in-laws as we’re on a livery. Although during testing in the summer last year it worked really well, when winter arrived we froze & there was no heat coming through although there was plenty from outside. They are at a loss & we face a 2nd year without any heating. We have a boiler we can use as a back up, but that also isn’t doing the job. I’m desperate to find someone who could have a look for us as the in-laws have given up on it. Do you know of any companies that deal in these areas? My Google searches have come up a blank.

    • PM to follow.

  41. Does the pump constantly circulate the water?

    • No, the pump cycles on and off in the same way that a conventional furnace would in response to a thermostat in the room. It’s an “on demand” system where the thermostat provides a “call to run” signal which is nothing more than closing a switch at a given temperature.

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