Compost Heating System




Posted in WorkshopEnergy

Introduction: Compost Heating System

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.

Step 3: Lay the Hydronic Loop

Coil 1/2" plastic pipe at the bottom of the mound and hold it down temporarily with cinder blocks. Run the end of the pipe outside of the ring of hay bales, to be connected to your water source.

Step 4: Chips and Sawdust!

Chip wood into the pile, intermittently stopping to throw shovelfuls of sawdust in. The high carbon content of both materials create a lot of heat when decomposing.

Step 5: Continue Laying Water Pipe + Building Up the Mound

Once you get started, this project should take 1-2 days of labor. Keep looping in water pipe and building up the hay perimeter as you add woodchips and sawdust. Throw in some manure - any animal will work - if you have any.

Step 6: Fill Line With Water

The Pain Mound can be used to heat hot tubs, greenhouses or hydronic heating systems. Plan out your location carefully ahead of time so that you are close to the thing you will be heating. In the diagram shown here, we hooked up a pain mound to a greenhouse. We buried the water lines so that we would not lose additional heat to the outdoor air.

For more information, has an excellent detailed installation guide, which can be found here:

Step 7: Track the Heat Output

If possible, consider including a series of temperature sensors with your water pipes, so that you can track the BTU output along the way. Our mound produced more than 6 million BTUs over a period of 12 months, including a freezing New England winter.

Collaborators: Garth Schwellenbach and Jesse Selman



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2 Questions

If I am right in my thinking is there a possibility to use other materials, such as autumn leaves, although they do not produce enough heat for as long as the wooden material, right?

Thanks for a very good web page! I am seriously considering building this for heating my home. I wonder about options for the hydronic loop, using heat cable instead. What would you think would be the best fitted kind of cable to use? Best regards from Sweden.


Can anyone tell me why plastic piping is always used as the coil?

1 reply

I am making one this year's and plastic is cheapest. I tried shop for copper or other tubing but the cost is prohibiting. like thousands of dollars as compared to plastic tubing being 230$

And....two more questions:

The wood chips shoud they be made from fresh trees or "dead" threes or maybe it doesnt matter?

How much and water did you add and did you do it all the time or just "like" each 10' or so....

Loooove you great instructions!!!

Still...whats the ideal size of the woodchips?

Hi, I am impressed! Will make it asap here in RO.

Just wanted to know how long did your pile last i am in Romania and fixing to build almost the same one you got there in the pics

1 reply

And please translate what means BTUs. I'd like to transfer to kWh. :) we mesure heat in different ways :) thnx for help ;)

1 reply

I'm sure you can do that, here's a tip: 1 BTU = 0,000293071 kWh

Nevermind. I just saw the graph. ... Another question. What was the overall cost of the set-up?

Piles of compost can catch fire spontaneously! Watch out when storing compost too close to your house.

5 replies

You are right! Some towns have a minimum height of 8' for compost/mulch piles, for that reason.

So, a small pile will catch fire easier than a large pile?

Oops, my apologies! That should be "maximum"...

That makes a little more sense. I just didn't know if there was some weird trick with heat dissipation in large piles or something. Contemplating making a fairly small one and putting it inside of a make shift greenhouse. Basically just plastic over a dome... Curious if it could keep it warm enough to start seedlings in the garden in late winter/early spring on Michigan. I don't have the space/money to make a big pile and get the pumps and pipe run.

The heat output should be sufficient but you must be mindful of the gaseous anaerobic decomposition byproducts. Concentrations can become too high and kill plant life.

This is some cool stuff

Hello, I have a quoestion here. What about rebuilding this system after these 18 months? Do you remove everything, like: hay bales, pipes? How do you do it?