Composting Hot Water Heater

In my quest to learn how to be more self-sufficient without modern power I recently attended Imagine Rural Development Initiative’s workshop on how to create a hot water heater with yard waste.  Danny (our gardener) was keen to go with me so along with Nicky (a colleague of Thom’s) we took off one Saturday morning to Imagine’s new training center for self-sufficiency in the Waterfalls area of Lusaka (off of Great East Rd. beyond the airport roundabout).

Co-directors Steven Putter and Jacqui Wintle met us with a small pamphlet that described the steps to creating a hot water heater with compost.  Here Steven is explaining the process to Danny (in the red hat) and a gentleman from Bauleni who owned a nursery.


Steven prefers to create an aerobic compost heap that utilizes the thermophilic bacterial process to break down organic matter into nutrient-rich compost.  Thermophiles use high heat (100-200 degrees Fahrenheit, with the ideal range being  125-160 degrees) to quickly kill pathogens and seeds and create rich dark brown soil.  The advantage of using the aerobic composting method is that it doesn’t smell and it produces compost in as little as four weeks. You can tell if your bacteria is thermophilic by inspecting the center of your heap.  Thermophiles are white chalky critters, shown below.







This workshop was a hands-on one so after he explained what we were going to do, we went to work.  Before you start your pile you have to gather up cut brush, leaves, grass and manure.  You need to find both brown and green matter.


It’s the dry season here (see photo) so there was an abundance of “brown” or dried/dead matter.  “Green” matter, like fresh cut grass, is a little scarce now, so in lieu of that Steven used partially decomposed mulch from an old compost pile.


The first step to creating a good compost heap is to lay out branches or thickish stalks as the bottom layer.  This allows for drainage of water and promotes air flow throughout the pile.

The next step is to spread a layer of brown matter — things like straw, dry leaves, newspaper (except glossy sections), cardboard, sawdust, etc. — on top of the sticks.


Here, Steven showed us how to roll the dry straw (brown matter) up into a ridge in order to form a structure for the heap (about 8-10 inches high).  Then, we filled in the heap with dried straw so the layer was all about the same height.




Next, we added the layer of “green” matter.

As above, Steven first rolled a layer of “green” matter to create a ridge, and then we filled in that layer.  (Here you can see that the “green” layer is darkish brown, wet, partially composted mulch, as compared to the completely dry layer of straw below it.)




On top of this layer Steven added five small piles of chicken manure (see the four piles in the corners and one in the middle below), to heat up the compost pile in order to ensure the appearance of thermophilic bacteria.


As we built the heap Steven watered each layer, because aerobic composting needs moisture.




After about three layers (brown, green, manure) came the hot water heater portion of the lesson.

In a compost hot water heater, water from a spigot runs through a hose that is placed in the center of a thermophilic (hot) compost heap.  Here, Steven wound a heavy-duty 50-foot hose when the heap was about half-way as high as the finished product, making sure all parts of the hose were separated by at least 5-7 inches.  One end of the hose was attached to a water spigot, the other end was attached to a shower head.  When doing this he cautioned to leave a couple of feet of slack on the shower head side, because the compost heap will flatten as time goes on and you don’t want the hose to pull off of the shower head because you didn’t have enough slack.  (He apparently learned this from experience, the best teacher!)

Another four layers or so were added on top of the hose layer.  The heap needs to be at least a yard high.


See the hose snaking in and out of the heap?  Steven is connecting the hose to the shower head at the top left of the photo.




And there you have it, a nifty outdoor shower, though you can snake the hose in a window and attach it to a shower head indoors if you want.  After two days I can verify that the water was so hot that both Thom and I snatched our hands away upon being scalded by it! If the thermophilic bacteria are happy then the water is at least 125 degrees.  The water was definitely too hot for a shower and needed to be cut with cold water.





In areas with snowy winters you can store loose dry brush and/or leaves as your brown matter in a barn or shed and then use the partially broken down sections of your current compost pile as your green layer.  To do this Steven sifts the current compost pile through a grate, uses the fine matter below as finished compost and uses the larger pieces of matter left on top of the grate as the green layer for his next heap.


Aerobic composting is an on-going process.  The piles need to be turned every four weeks or so to ensure the oxygen flow needed for the decomposition process.

A couple of notes.

First, it’s important to have a heavy duty hose so that the compost doesn’t leach into the water, and you might want a thin layer of the brown matter on the top and bottom of the hose layer so that the chicken manure is not directly touching the hose.

Second, if you want to have a consistent hot water supply, then you need to create rotating compost piles as they’ll lose their heat after a few weeks.  You’ll need to experiment in your specific neck of the woods to see (a) how long it takes for the pile to heat the water (here it’s about 2 days), and, (b) how long it takes for the pile to cool (~3 weeks).  Then, you’ll need to time the creation of your next compost pile to coincide with the cooling of your current one.  By keeping four compost heaps going you can pretty much ensure a steady supply of hot water.  Here’s a sample schedule (using the two days to hot water that lasts three weeks schedule):

  • Pile 1 – Create on Jan 1, hot water Jan 3-24, turn over Jan 31 to start a new pile.
  • Pile 2 — Create on Jan 22, hot water Jan 24 – Feb 14, turn over on Feb 21 to start new pile.
  • Pile 3 — Create on Jan 31 (from pile 1), hot water Feb 3 – 24, turn over March 1 to start new pile.
  • Pile 4 — Create on Feb 21, hot water  Feb 23 – March 14, turn over on March 21.

Third, you need the heap to be large and tall.  This  heap was about 1.5 yards wide and about the same height.  And, you need to keep it moist, but not wet.  You can cover it with a tarp to retain moisture in dry seasons and prevent too much wetness in rainy seasons.

And there you have it! An all-natural hot water heater.



About Kimm X Jayne

Gravatar Photograph from the exceptionally talented Ben Heine.
This entry was posted in About Zambia, Permaculture and tagged , , . Bookmark the permalink.

7 Responses to Composting Hot Water Heater

  1. ang says:

    Pretty cool!

  2. Stuart says:

    Interesting idea. Hate to be such a stick in the mud, but doesn’t Zambia have lots of sun for warming water?

  3. Ah yes, the compost heap in my paddock is the favorite winter resting place for my flock of sheep. So warm that steam rises off of it. They would rather be outside on the warm compost with snow on their backs, than inside out of the wind and moisture.

  4. Leslie says:

    This is very interesting. So all of those compost piles would be built near each other around an outdoor spigot? And you coil the hose back and forth within the pile?

  5. medwoman says:

    Reblogged this on Send Seeds To Africa and commented:
    We should try this Fredrick!

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