BuildingEnergy SystemsWaste Systems & RecyclingWaste WaterWater Conservation

The Rocket Powered Shower

rocket-powered shower diagram

Plan for our Rocket-Powered hot water system for the Basecamp shower + bath block

Spending all your day gathering sticks for a hot shower is just no fun. No fun at all. Mind you, anything that results in a hot shower (or even better, a hot bath) has to be considered a priority at Milkwood. So when Nick finished converting the old ‘Sunbeam Sheep Shower’ structure (basically a new-fangled sheepdip) to a shower block with a little wood-fired, home-made firebox thingamy to heat the water for the shower and the bath, that’s what we did. Lots of stick-gathering.

The romance of wood-fired hot water quickly wears thin, however, if your water-heating system is not terribly efficient. Because this means the system requires a fair deal of wood to heat the water, which therefore releases a corresponding amount of CO2. And also results in lots of stick gathering. So Nick went searching for the most super-efficient, super-simple and super-funky heating system idea he could find, which could then be converted to a water heating system. And thus we discovered the glory that is the Rocket Mass Heater.


Nick Ritar + Si Horsely cobb around the burn chamber and firebricks to protect them

The basic premise of a Rocket Mass Heater is that the heat energy of a small, very hot-burning fire is used in a optimal way to get the utmost out of that heat energy. Hyper efficiency with minimal fuel input. Ianto Evans + Leslie Jackson, a couple of Permies who are prettymuch gurus on this subject, put together a great little book called Rocket Mass Heaters and this was our inspiration and guidebook for our project. The heat of the small fire is drawn up through a vertical heat riser of some kind, which creates an updraft and therefore causes the fire to burn extremely hot. A hotter burn means less smoke. And less smoke means more hot water per handful of sticks.

Then the hot gases in the riser is put to work – pushed (or pulled) under hot plates, past water boilers, underneath cobb benches, through thermal mass walls – wherever you need to heat. By the time the hot gases make their way out to the outside world, they are spent, and much cooler – the heat energy has been transferred along the way to whatever needed to be heated. Hurrah!


The completed system – two days work, all told

Rocket Stoves are quickly catching on in various places around the globe – because they’re so fuel efficient, for example, they’re being used in development aid projects where fuel is scarce. And because they’re super simple, they can be made by prettymuch anyone with a need, a plan and some simple tools. There’s a stash of great Rocket Stove projects that have been done around the world at

But back to us at Milkwood. The making of our Rocket-Powered water heater took two days for two blokes. The above diagram explains it all pretty well. Firebricks in a pattern with a burn chamber in front, topped by an insulated heat riser, topped by a small heat exchanger, topped by a chimney. The water came in one end of the system from the bottom of the water tank, then passively circulated between the heat exchanger and the hot water tank (just a normal hot water tank like you would have on your normal western hot water system) once the fire was going via simple pipes and the power of convection. A handful of sticks in the burn chamber set the fire going. Then we waited and finally turned on the shower tap and… voila. Steaming hot water for one shower. Hoo-bloody-ray.

Post-wash, the water flows into a greywater trench which waters a planting of She-Oaks (Casuarinas) downhill from the showerblock. These will, in time, yeild excellent stickwood for the fire, as Casuarina wood is some of the hottest burning wood in the world. Which is the closest we’ll come to closing the loop (in terms of energy, carbon and responsibility) on our daily shower anytime soon… which makes for a very happy shower.

sticks ablaze

A handful of sticks is all you need…

Here’s a Flickr set of the construction process – it should give you a good idea, it’s fairly thorough. Feel free to ask questions if you like, I’m sure Nick would love to wax lyrical about his beloved Rocket construction.

So viva la Rocket Stove. These things are hyper-efficient. They should take over the world, I reckon – what is a better beacon for sustainable, responsible living than a guilt-free hot bath?

nick in the shower

 Happy Nick bathing in the glory of his Rocket-Powered Shower

**Notes on this system for safety: you want a pressure relase valve on the hot water tank (most have them on already) so the water tank doesn’t explode, and also a tempering valve on the hot water outlet (so no water hotter than 60º comes out), so that no one burns themselves during their lovely wood-fired shower.


  1. Hi Nick,
    you certainly look as though you are enjoying that shower. We are just about to design something similar, depending on what plumbing parts we can come up with.
    Would like to clarify something.
    My understanding is that from the fire onwards (until the main combustion has happened) needs to be insulated, your design shows firebricks around the intial stage, which would absorb heat for a while ??? any comments ?? The first Rocket stove we built we used a mix of clay, and paper mache which shapes really well, and will not burn (flame) as long as the paper content is less than 80%. In fact much of the paper does burn out but this only increases the insulation effect. We put a thin plaster layer with high clay/sand inside the chamber just to protect the paper/clay mix Pumice and clay is good too if you have a handy source of pumice. Thanks for sharing your good work


  2. Hi Bob,

    The firebricks were very low thermal mass insulating brick (factory seconds that were purchased for 50c each) so they don’t absorb much heat at all, keeping the fire very hot.

    We painted the exposed surfaces near the feed chamber with a thin coat of fire cement to stop the brics chipping, they are quite fragile.

    The heat riser is insulated with vermiculite which we picked up at a garage sale.

    Your clay/papier mache sounds just the ticket :)

  3. Looks cool. I’d love to see a version that runs the smaller arm of the stove pipe (before the crook) under the shower floor. That way, the shower floor would be slightly heated, like a Kang Bed. You could shower in the late fall with no discomfort.. hot water and warm feet :) Maybe build the shower wall out of dark stone and facing the noon sun, get that nice heat radiating back to you for your evening shower (open shower door in the winter to collect heat, closed in the summer)

    So now you have to get started on the second part — water chilled by cool air coming from tubes buried in the earth.

    love outdoor showers.

  4. I am building a green house and would like to have some water heated growing beds and maybe benches.could the rocket stove be useful for this could it be designed for use with long sticks? I have a portable saw mill and often have lots of saw mill stickers slabs etc.

  5. Gerald —

    I’m just a curious onlooker, w/ no heated growing beds or greenhouse experience.

    I know you could try to use a Kang Bed type system to create a large heated surface area that has slow/long heat release. It’s basically a stove, and the pipe snakes through a ceramic slab (or bricks — similar to the top of this system.) A little bit of heat warms the stone and creates a really great heat release all night long. They’re a centuries old tradition native to central/northern Asia. I slept on one, in a small courtyard house room w/ torn paper windows, in the dead of a Beijing winter (in the mountains no less), and was hot enough to only use half a blanket. You can find diagrams on google.

    Or maybe you could build something where compost could heat from below the beds.

  6. Hi Nick, great to see you built the rocket. I was just wondering, the cold water outlet from the cylinder is much lower than the point it goes into the heat exchanger. Does the passive circulation from the heater drive the water up that rise? Or is it pressure? I always imagined that the cold outlet had to be higher than the point it goes into the heat exchanger, to ensure the hole tank load get heated…

  7. We are in the process of purchasing 300 acres off grid in South Burnett, Qld. Mountains of old felled timber, which we would like to put to good use. I grew up with having to “light the Donkey”, with endless hot water for minimal fire and am stoked to see your version. Ours were much more glamorous – more like beautifully kept little crematoriums, rendered and painted. I am interested to know just how far we can wood-fire/solar/gas power a weekender cabin, and still be able to run my internet based business from ‘home’. Any pointers?

  8. As much heat as these units are capable of putting out it would seem somewhere off of this type system a low intensity small steam engine could run a car alternator or two to help keep a battery bank charged. If the lighting in the cabin were LED,( think 12v dc.), water heating was by this furnace, as well as heat, then a bank of batteries and a protected inverter should seem all you need to run your computer and a Hughes Net satellite internet interface. If you go all the way following the full path from feed to exhaust for maximum efficiency one could rig a condenser style unit into the end of the chimney to condense the exhaust moisture to water plants or survive. If your unit is really efficient and all you are getting out the chimney is co2 and water then during the winter you could pump part of it directly into the greenhouse. How about a small one to turn waste water to steam so it can be reclaimed for irrigation? If one set down and really engineered this thing to the maximum it might be all you need period. You get heat, hot water, electricity, and irrigation water from a mass furnace. Think like NASA going to Mars. Use or reuse everything like there isn’t going to be anymore of it.

Leave a Reply

Your email address will not be published. Required fields are marked *

Related Articles

Back to top button