The Potential for a Compost Water Heater


Yesterday I walked up to the big galvanized compost pile I created and was amazed by how much heat was radiating from it.

That’s the pile I built in this video:

It got me thinking again for the umpteenth time about the potential for heating water with a compost pile.

At our house there is a sweet solar water heater on the roof which provides abundant hot water… except on rainy days. The compost pile made me wonder: what if the water from that heater were backed up by a compost pile water heater like this article describes:

“…the basic idea behind a compost water heater is that tubing is coiled throughout the compost pile and then filled with water, which in turn is heated by the compost pile.

As the below image illustrates, cold water goes into the coiled tube and hot water comes out. Not only that but it’s also possible to extract methane gas from the compost pile, which can then be used for cooking or heating.

Thermal compost pile

Looking back at the work of Jean Pain, his compost piles built with wood chips were massive. In some cases, he was employing 60 tons of compost in a single pile to provide his energy needs. More recently, however, experiments have used piles that are as small as 6’ x 6’ to create a similar effect. Some of these modern piles are producing temperatures of 150°F or more.

The trick to improving the original design is the use of more polyethylene tubing. In the typical 6’ x 6’ compost pile mentioned above, you might expect to use at least 300 feet of 1 inch diameter polyethylene tubing. This tubing is carefully coiled and layered in between the layers of compost to repeatedly heat the water as it moves through the various layers of the coil system.

As a general rule, the pile will start with a compressed layer of compost followed by a layer of coiled tubing followed by a layer of compressed compost until you reach the desired height.

Since a compost water heater does not have a hot water tank, the tubing becomes the “tank” in this example. This means that the more tubing you use, the more hot water you will have available at a given time. Think long, relaxing shower versus being the last one in the house to get a shower before work.”


Just thoughts for now.

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