How to build a compost-powered outdoor, hot water shower system

The pile of compost is almost ready for making hot water. Picture: Hannah Moloney
The pile of compost is almost ready for making hot water. Picture: Hannah Moloney

To say I'm pumped for this method of heating water is an understatement - for years the compost-powered shower system had been on my list of awesome things to build.

Originally developed by French man, Jean Pain, the system has been replicated and adapted all over the world, including in our own region.

Basically, a coil of pipe sits inside a compost pile that feeds hot water to a shower. The water inside the pipe is heated by the natural warmth inside the compost. We got our shower water up to around 60 degrees Celsius.

We made our first compost-powered shower system for a two-week permaculture design course that we hosted at our community garden a few years ago.

While we live in a fairly moderate to cool temperate climate, others with heavy snow also do this to heat water over freezing winters. So you can drop any thoughts you might 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.

A brief introduction to 'hot compost'

Hot compost is where you arrange layers of carbon and nitrogen-rich 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.

Establish the footprint of the compost pile. Picture: Hannah Moloney.

Establish the footprint of the compost pile. Picture: Hannah Moloney.

Building your compost pile

Just like making any other hot compost system, layer your carbon and nitrogen materials to establish the footprint of the pile (about three metres in diametre) and set up the internal pipe system.

Ours consisted of four star pickets as the framework and 25mm of poly pipe tied onto it. It's recommended to use 100m of 50mm rural polypipe, but we decided to use 25mm 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 as it drastically increases the volume of water that can be heated up at any one time in the pile.

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.

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 prevent it from heating up evenly.

Placing wire around the edge of your compost helps 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.

To speed up the heating process you can cover the pile with tarpaulin or any insulating layer, like straw bales.

To measure the heat at the centre of your pile, make sure to get a long thermometer stick to avoid having to dig hole in the side and compromising its heat retention capacity.

INGENIOUS: A coil of pipe inside a pile of compost creates a clever hot-water system for an outdoor shower. Pictures: Hannah Moloney.

INGENIOUS: A coil of pipe inside a pile of compost creates a clever hot-water system for an outdoor shower. Pictures: Hannah Moloney.

Shower stalls

We built the shower block from timber pallets salvaged and shower bases. For privacy we covered them in sheets as it was summer time. But, 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.

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.

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.

The outdoor hot water compost shower in action. Picture: Hannah Moloney.

The outdoor hot water compost shower in action. Picture: Hannah Moloney.

So ... did this hot water system work?

The short answer is yes, we successfully 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 five minutes at the most - which is more then enough. The recharge wait between showers was somewhere between five to 15 minutes depending on how many people wanted to have showers.

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!

  • Hannah Moloney and Anton Vikstrom are the founders of Good Life Permaculture, a landscape design and education enterprise regenerating land and lifestyles.