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. MOTHER EARTH NEWS STAFF

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). PHOTO: MOTHER EARTH NEWS STAFF

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.)

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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.