Build A Compost Water Heater For Hot Water Abundance

Categories: DIY

It’s a water heater and it’s also a compost pile. That’s correct, compost: that same pile of decomposing organic material you’re naturally accumulating from your own backyard homesteading operation.

While you’re probably well aware that keeping the sweet-spot ratio of 1-to-1 on the mound’s carbon/nitrogen levels makes for ideal fertilizer in the spring, have you ever noticed that gargantuan hunk of bio-stuff steaming like a sauna in the middle of February? Believe it or not, that’s basically your homestead’s leftover organic material, releasing its energy in the form of heat. And that’s energy we can actually use to heat our homestead’s water supply.

The Pain Mound is a large pile of woody biomass, aka mulch. Invented by French farmer Jean Pain in the 1970s, it is made of woodchips and sawdust, surrounded by a ring of hay bales for structure and insulation. As the Pain Mound decomposes, heat is produced and harnessed using a hydronic loop. The Pain Mound will produce heat for up to 18 months, after which time the remains (nutrient rich, earthy humus) can be used to build soil.

Step 1: Lay Out the Mound


Stake out a circle approximately 12 feet in diameter. Purchase hay bales from a local farm, collect fallen trees and branches, and rent a chipper. A load of sawdust can usually be procured from a local sawmill: they will often deliver for a nominal fee.

Step 2: Create a Hay Bale Backstop + Add Aeration 

Lay about 15′ of perforated 4″ tubing at the bottom of the mound, with each end protruding out of the perimeter. Create a “backstop” of haybales to catch the woodchips as they are thrown from the chipper into the mound. Chip a layer of woodchips approximately 1′ high into the mound on top of the aeration pipe.

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