We recently made our first compost powered shower system for our two week permaculture design course held at Okines Community House and Garden.  This is a method originally developed by French man, Jean Pain and has since been replicated and adapted all over the world. While we live in a fairly moderate/cool temperate climate, others with heavy snow also do this to heat water over freezing winters like Ben Falk in Vermont (skip to 2:20 in this video). So you can drop any thoughts you night have that this will only work in a warm climate. Hot compost is hot compost regardless of the climate.

This method is traditionally based on using mostly woodchips and water, we used aged woodchips and aged chook poo (layered fairly evenly) plus water as this is what we had available to us.

• Before we go any further, we must say a special thanks to our friends over at Very Edible Gardens (VEG) for showing this particular version and answering approximately 100 of our questions.

A brief introduction to hot compost

Hot compost is where you arrange layers of carbon and nitrogen materials like a lasagne with water in between. It needs to be at least one cubic metre for it to heat up, with the desired heat being around 60-65 degrees. This is hot enough to kill off bad pathogens, any hotter and the good biology can suffer. For this particular system we’re wanted it to get as hot as possible as heating water is our focus, not compost for the garden. However saying that, this compost will eventually be used in the local community garden where it was built which will still be beneficial to the soil once it’s had a rest. You can read about how to make hot compost for your garden here. 

First step

Just like making any other hot compost system, layer your carbon and nitrogen materials – wedid a couple of layers to establish the footprint of the pile (around 3m in diametre) and set up the internal pipe system. This consisted of four star pickets as the framework and 25mm of poly pipe tied onto it. Dan and Carey from VEG recommended using 100m of 50mm rural poly pipe, but we decided to use 25mm pipe as we could then use it easily on our property once the pile is dismantled. If we had our time again we would use the 50mm – more on that later. 

Second step

We filled in the polypipe’s centre with layers of woodchips, chook poo and water – basically a mini hot compost system to make sure it would heat up evenly like the rest of the pile. Note the mini bob-cat machine. We hired it for the day as we didn’t have 20 people on hand to shovel the 20m2 of organic materials – it made the job possible and made us laugh. Imagine three people over 6 foot taking it in turns to drive –  like giant clowns in a tiny box car…

Water is key to any hot compost working – we alternated between the sprinkler approach (having it running on top of the internal pile) to having two people stationed there with hoses, watering in each layer thoroughly. You really don’t want any dry patches in your pile as this will preventing it from heating up evenly.

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Step 3

Put wire around the edge of your compost as seen below. This helps you build a pile with as much volume as possible – maximising the space you have and ensuring there’s plenty of mass to heat up. Only once you reach the top of the wire will the pile start to taper off into a pointing tip.

Blake the legend watering in the pile from the top!

The shower stalls

We built the shower block from timber pallets salvaged from building sites and shower bases from the local steep shop, for privacy we covered them in sheets. The stalls were located as close to the compost pile as possible so the hot water leaving the pile didn’t have far to travel – meaning it wasn’t going to cool down before it got to the actual shower head. In the photo below left, you can also see we insulated the hot water pipes leading up to the shower head. 

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The greywater system

We needed to design and build a temporary greywater system to filter the water coming through the shower before it hit the neighbouring wetland. We made a simple, safe and effective bathtub system to do this job. We lined two baths with old doona covers, filled them with coarse woodchips and ran pipes from the showers to them, using gravity to move the water where it needed to go. The woodchips act as a filtering sponge, as water moved through them any grease and soaps were caught meaning the water leaving the system was filtered and safe to enter the beautiful wetlands which lead straight to ocean a few hundred metres away.

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So…. Did it work?

The short answer is yes, we successful showered 30 people over two weeks, averaging around 10-15 each day (spread over the morning and evenings). As expected, people only had short showers up to 5 minutes at the most – which is more then enough. The recharge wait between showers was somewhere between 5 – 15 minutes depending on how many people wanted to have showers.

Thermometre showing 60 degrees and Anton the babe enjoying his first hot compost shower. 

What would we do differently next time?

Quite a few things…

• Use bigger pipe (as we were told to do). We used 25mm instead of 50mm pipe as we could easily use that in our irrigation system afterwards. What we didn’t think through properly is that this drastically decreases the volume of water being heated up at any one time in the pile.
• Cover the pile with the tarpaulin (or any insulating layer, i.e. strawbales) the day we built the compost and not one week later. To be fair, there were *crazy* winds on the day we built the pile so it wasn’t going to work. But a week later, the pile had definitely heated up to 40-50 degrees but the showers were only luke warm at best. So we added the tarpaulin to it and the next morning – boom! The heat was up in the 60s and showers were hot. Our friend Nick from Milkwood tried to reassure us that it would have heated up anyway with a bit more time, as it’s just such a big compost pile. While he’s probably right, the tarp seemed to help bring it home *quickly* which we really needed for the course.
• Get a longer thermometer stick – the thermometer you can see above only had a stick 45cm long. As the pile was 3m in diametre that meant we couldn’t gauge the centre of the pile’s temperature without digging a little hole in the side and compromising its heat retention capacity. So we just left it to measure the outer edges of the pile – which was still reading around 60 degrees after three weeks.
• Make the shower stalls a but more weather proof. While it’s summer and mostly warm and lovely in Tassie, we still get days where the wind blows and you reach for your jumper. If we had more time and resources it would have been preferable to make the shower stalls a bit more solid with a roof and solid door. This design would be perfect for the warmer parts of the world!
• It wasn’t as affordable to build as we had hoped. In the end we had to pay for all organic inputs, hire someone for two days to help build it, buy random bits and pieces and hire the machine – coming in at just under $1500. In theory we were going to source woodchips for free from the Council, organise a community working bee to shovel everything and just pay for some nitrogen (chook poo). Next time, we might think a bit harder about how to bring this price done to make it more viable. Of course, if you live on a farm with lots of resources it’s likely you could do it for under $500.
• Talk to the school across the road 6 months ago…. We built this pile because we were told there were no showers within easy walking distance. The day before the course, when we were a bit worried about whether the pile would heat up enough (and we eventually added the tarpaulin) I went, stuff it – even though we’ve been told there’s no showers in the school I’ll just go check. Turns out there was a whole shower block 150m from us and they handed me the key in two minutes and happily let us use it as a back up for the two week course. To say we felt a but silly is a gigantic understatement – swear words were mentioned. On the major up side, we got to build a compost powered shower, how cool is that!!! I’ve wanted to do it for years and overall, learning new skills trumps feelings of silly-ness (eventually).

Would we do it again?

For shizzle! Despite the long list of “stuff ups” above, I’m so pumped for this method of heating water. For years it’s been on my list of awesome things I want to do – adding to my skill set and now it’s firmly lodged in my head, heart and hands. I look forward to making our next compost shower – it’s going to be a walk in the park after all the things we learned from this time round!