Second Generation Compost Heater

Test results from the second generation compost heater MOTHER EARTH NEWS' researchers designed significantly improved on those for the first.

| September/October 1980

  • 065 compost heater - wrapped core
    The internal core was then wrapped in a series of coils of 1"-diameter black semiflexible plastic tubing, which—in the completed pile—carries the to-be-heated water
  • 065 compost heater - core
    Mother's second experimental compost heater began with a "core" of material to be composted (consisting of three parts wood chips for every one part manure) that was held in place by a pole-supported chicken-wire cage. (This inner heap measures a full six feet wide by eight feet tall). 
  • 065 compost heater - water tank
    In an experimental attempt to increase the heap's ability to maintain and store a supply of hot liquid, a 30-gallon water heater tank was ""plumbed in" to the line, and then buried in an outer three-foot layer of chicken-wire-supported compost.
  • 065 compost heater - wrapped pile
    The entire structure was then covered with a wrapper of heat-gathering black plastic.
  • 065 compost heater - diagram3
    As the chart shows, our second generation compost heater was putting on a pretty impressive performance this summer!

  • 065 compost heater - wrapped core
  • 065 compost heater - core
  • 065 compost heater - water tank
  • 065 compost heater - wrapped pile
  • 065 compost heater - diagram3

As many of you undoubtedly know, MOTHER EARTH NEWS has for some time now been researching the use of large mounds of (primarily) vegetable matter to produce heat. We first introduced our readers to the concept in the story "The Genius of Jean Pain," which described the pioneering work done in France by M. Pain ... a noted energy experimenter and one of Europe's foremost organic gardeners.

Inspired by what we'd seen and heard while visiting Jean, we soon decided to begin doing a little compost-heat experimentation on our own. It wasn't long before MOTHER EARTH NEWS' researchers had a prototype heap "up and running." That initial pile was completed on December 14, 1979 and by the 24th of that same month had reached a core temperature of 120°F.

Our experimenters were somewhat disappointed to note, however, that the heap never got any hotter than 120°F (although Jean Pain's mounds were reportedly able to achieve temperatures of 140°F). Furthermore, MOTHER EARTH NEWS' "decomposition oven" held its peak heat for only 5 1/2 weeks before a long cold snap caused the internal temperature to drop slowly. The French researcher's compost piles, on the other hand, are said to be able to maintain their higher temperatures for as long as nine months!

The discrepancies between M. Pain's results and ours, we decided, could be attributed to several factors. For one thing, the Gallic gardener uses massive 50- to 100-ton heaps, while our initial experimental pile probably weighed no more than five tons. In addition to that, we were sure that the exceptionally cold—for North Carolina—winter temperatures (below freezing, night and day, for over a week) played a part ... as, perhaps, did our compost "recipe." (It seems that Jean Pain uses very thin wood chips, and allows the brush's own foliage to provide the compost's "starter." We, on the other hand, worked with larger chunks of wood ... combined in a four-to-one ratio with manure.)

Try, Try Again

 Spurred on by what was certainly a successful—if not overwhelmingly so—initial test, MOTHER EARTH NEWS' researchers soon set to work putting together a second experimental pile which would, we hoped, produce results more nearly equal to those that M. Pain has been able to achieve. Our first thought was to obtain a shredder which could reduce raw underbrush to the 1/16" slivers that the Frenchman uses for his compost. Unfortunately, reasonably priced chippers capable of such fine work aren't available in this country (at least we couldn't find any), and the cost of importing a machine as massive as those of M. Pain's design was prohibitive.

So, being unable to duplicate Jean's heating structures, we decided to modify our own previous design. To do so, MOTHER EARTH NEWS' researchers first built an inner enclosure of chicken wire that was six feet wide by eight feet tall. The cage was then filled with a 3-to-1 wood-chip/manure mixture (as opposed to the 4-to-1 mix that made up our first heap) and wrapped with coils of 1" black semi-flexible plastic pipe.

Michael Lyman
11/15/2012 7:07:39 PM

a.I disagree that the end product is the same. When you burn something, most of the carbons are released into the air as various carbon componds, thus they are lost and are contributing to air pollution. This does not occur in composting. b. I haven't removed the compost yet as this is the first heater I've built, but I am anticipating it to be a fair amount of work, done by hand, back, shovel and the back of my truck. I built the fencing in pieces to make it easier to remove with the material still in it and am hoping this makes it easier to get the layers off. c. I did the majority of the work constructing the pile by myself, I had help from one person for the first third of the construction. In my view, the use of the tractor consumes far less in regards to resources as gathering firewood does, when taking into consideration the fuel spent getting a permit and making multiple trips up the hill to find and buck the logs. It took 3 loads in my dads dumping trailer totaling about 40 miles round trip. This is an experiment through and through. I will still be burning wood, just not as often I hope.

t brandt
11/15/2012 10:50:09 AM

a) Oxidation is oxidation. Long chain carbon molecules are turned to co2. Fire is rapid; bacterial metaboism is slow, but the end product is the same. The heat is stored as energy in the chemical bonds of the fuel. It's only the rate of release that differs. (b) Perhaps I should have phrased the question like this: The spent compost looks like it would be very difficult to evacuate thru all the fencing and coiled tubes. How do you do it? (c) The article clearly states that the system was built by a team of workers using a tractor.

Michael Lyman
11/15/2012 3:39:10 AM

Well, first of all, they aren't really the same process. Burning is a chemical reaction and composting is a biological process. Also, I have used firewood as my only source of heat for the last ten years and I can honestly say building this pile was much easier, and didn't require a "team of workers". As for the 5 tons of "spent nuclear fuel", we do lots of gardening here and I plan on using it for compost. I also live in an area where compost is a viable commodity and I can always sell it for more than it cost me, which would be all profit since I acquired the material for free. The what do you do with question seems especially odd to me, with a little imagination I'd think most people could come up with something.

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