CompostEnergy SystemsGeneralHow to

How to Make a Compost Water Heater

Everyone loves hot water in the home, but the ecological cost of long, hot showers powered by fossil-fueled water heaters adds some guilt to those long hours in the bathroom. What if you could have a huge supply of hot water heated by the compost pile in your garden. Instead of greenhouses gasses, the byproduct of your hot water would be more fertile soil.

The Ecological Cost of Heating Water with Fossil Fuels

It is undeniable that a home without hot water in the United States and most of the other industrial world is considered to be a poverty-stricken household. Hot water is an indispensable feature of our homes that we have come to depend upon.

What few people realize, however, is that the process of heating water in homes is extremely energy intensive. Hot water heaters are the second biggest users of hot water in the home. Furthermore, most modern built homes have massive, tank-style water heaters installed so that you can enjoy unlimited access to hot water at any time of the day.

Since energy use is doubling every 20 years or so in the United States, and since we still depend on nonrenewable fossil fuels for most of our energy consumption needs, the ecological cost of water heating is enormous. The warm showers that you so enjoy are most likely at the same time contributing to massive greenhouse gas emissions leading to global warming.

An Outline of the Jean Paine Method of Heating Water

Luckily, there are other ways to heat the water that you use. If you heat your home with a wood stove (one of the most ecological and sustainable ways to heat a home), you can easily adapt your wood stove to also heat the water you use. If you live in areas that receive ample sunlight, a solar powered water heater is another option that can get you the hot water you need without dependence on fossil fuels.

Whereas some people might live in areas without access to abundant sunlight or timber for wood fuel, you can make up a compost pile pretty much anywhere. Compost is nothing more than the art of putting together certain organic materials in such a way to help speed up the process of decomposition to get quality top soil.

Most all gardeners and many environmentally conscious people have some sort of compost pile brewing somewhere around their house. There simply is no better soil for plants than a well-made compost. However, very few of us have ever considered other uses we can get from that slow decomposition process of our compost piles.

If you have ever turned over a compost pile, you know that inadvertently sticking your hand into the middle of the pile can cause minor burns. Thermophilic microorganisms, or tiny heat-loving “bugs” take over a well-made compost pile and help to break down the organic matter into a rich, nutrient dense hummus.

Thermophilic microorganisms are critical to quality compost because they help to kill off any potential pathogens that could exist. Since thermophilic organisms will work inside a compost pile for several weeks or months (depending on the size of the pile) during the slow process of decomposition, right outside your home is a sustainable source of heat that is naturally occurring, renewable, and about as “green” as can be.

Jean Pain was a French inventor who developed a compost-based energy system. Pain saw that the excess heat produced by compost piles as a potential energy source for our homes. His water heating method, known as the Jean Pain Method, basically runs water piping through the inside of a thermophilic compost pile before directing it inside towards a shower head or water faucet.

If you have ever turned on a water hose that has been left sitting in the hot sun for several hours, the first bit of water that comes out is usually pleasantly warm to the touch before the cold water comes bursting through. The Jean Pain water heating method works on this principle and in its simplest form, can be nothing more than a long, plastic water hose coiled through a compost pile and leading to an outdoor shower.

How to Set Up Your Compost Powered Hot Water Heater

For people who are looking for a more advanced system than simply showering underneath a hose, the Jean Pain method can be adapted to any home. If your home already has a plumbing system installed, the most important step would be to reconsider whether you need hot water available to all the different faucets and other areas of water use.

Washing dishes with cool water is a whole lot more bearable than taking a cold shower on a cold winter morning. Instead of redoing your entire plumbing system to allow for compost powered hot water, you could simply redirect the pipes heading to your bathroom to allow for hot water into your shower. Another option would be to simply run water from an outdoor spigot through your compost pile and into your bathroom where it can be connected to the shower piping.

To increase the efficiency of the water that moves through your compost, it is preferable to invest in copper piping. A copper pipe that is coiled throughout a compost pile will heat up faster and hold heater longer as it travels to your showerhead. Furthermore, the longer the water is in the compost pile, the hotter it will become. Building a bigger compost pile and coiling your piping as much as you can helps to increase the amount of hot water available.

Wood Chips Versus Other Compostable Materials

Another important consideration for your compost powered water heater system is what types of materials to use in your compost pile. The more traditional garden compost pile is mostly an assortment of materials that are easily decomposed such as animal manure, leaves, kitchen waste, etc. In the gardening world, the quicker the compost is ready, the better. Turning your compost several times a week is a strategy many people use to increase the rate and speed of decomposition.

If you are building a compost pile for hot water heating, however, you will want a slower decomposition process. Ramial chipped wood, more commonly known as wood chips or landscape mulch, is a great option for your compost water heater.

Wood chips decay much more slowly than other organic materials such as leaves, hay, straw, etc. The lignin in wood can only be broken down by fungi meaning that your wood chip compost pile will be a fungal dominated compost instead of the more common bacterially dominated compost preferred by gardeners.

A large pile of wood chips will take anywhere from 1-2 years to break down (depending on the size of the pile). Jean Pain preferred to use saplings, branches, and underbrush for his compost piles when he was developing his bioenergy heating system.

In our industrialized world, woodchips are abundantly available, especially from energy companies and local governments who are continually trimming trees to keep power lines clear. One call to your local energy company might get you a dump truck load of free wood chips which could heat your water for several years.

Greenhouse Gas Emissions or Fertile Top Soil?

The first step to a more sustainable livelihood is questioning whether the excesses of our industrial lifestyles are necessary. While hot water in our homes is a nice luxury, do we really need 30-minute showers or hot water laundry? If we are willing to embrace a lifestyle of necessary limitations, we will find that there are several ways to continue to enjoy the necessities and comforts of life in a more sustainable way.

The compost pile behind our home can easily be adapted to offer us all the hot water we need for our showers. Instead of greenhouse gas emissions, the by-product of our hot showers would be fertile top soil to spread on our gardens.

Tobias Roberts

After working in the development industry for over a decade, Tobias decided it was time to stop advising Central American farmers how to do things if he didn´t have a piece of land to live coherently with what he taught. Together with his family he runs a small agro-forestry farm, tourism cooperative, and natural building collective in the mountains of El Salvador.


  1. I looked at this years ago but was put off by one potentially life-threatening flaw: how to prevent the hot water becoming a breeding ground for legionnaires bacteria. I now have a hot water heat pump and that has to get up to 75c for 5 hours or so every week in order to kill the bacteria.

    Legionnaires bacteria loves hot stagnant water, and that’s exactly what you could get with a system heated by compost.

    1. Only an issue if the water sits around in a holding tank without being fully replaced frequently, or heated to a temperature high enough. The water in the pipe is replaced every time you use some water, not really stored for long enough to worry about Legionnaires.

      I do wonder at the target audience for this piece though.. most people reading this probably have hot water already – although I don’t! I’ll probably go a combination of solar evacuated tubes and wood heater “wetback”. The compost method could be an excellent cost effective solution in the meantime.
      Wouldn’t you want the compost heap to be as close to the shower as possible then?

    2. Could you run the water through a small UV filter before it came out of the tap? Tocombat the thrwat of Legionaires?

    3. Could you run the water through a small UV filter before it came out of the tap to remove any potential Legionaires bacteria?

  2. I agree with Anthony, although I consider an evacuated tube solar water heater with an electric back-up (preferably also solar) as a more ecological method than heat pumps.
    My shared solar heater also does the once a week higher heat.
    The heat generated by well made compost heaps is best contained for deactivating weed seeds and antibiotics.

  3. Solid fuel water heaters were once common in Mexico (Megamex) and seem to have become popular in India:
    Sort of a giant Kelly Kettle:
    (Note: Flames shooting out the top is a sign of incomplete combustion in the firebox and poor heat transfer to the water. Application of rocket stove principles would improve the situation for Kelly Kettles and probably wood fired water heaters.) While solar is nice, sometimes you can’t wait for a sunny day.

  4. I’d like information about using this method to heat h2o for a radiant floor heat system. Also considering using this to heat my driveway to eliminate shoveling and plowing. I live in PA.

    Have any of you done this or have read anything? Links appreciated. Thank you in advance.

  5. 140 degrees to kill all bacteria if solar or other means of heat seems like a lot till one considers he extra heat isn’t that much to add to already hot water.. umm a real ‘hot’ water heater instead of just water heater

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