Author: Dan Palmer

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Joel Meadows talks through his charcoal retort oven

Alt-tech workshops team member Joel Meadows has just completed this amazing piece of alt-tech wizardry – allowing him to simultaneously create top-notch charcoal for his forge and cook dinner at the same time! Then, after dinner, he can go make another knife or something in his charcoal-powered forge (which in turn he can use to slice tomorrow’s pizza).

A Rocket Oven to Call my Own

Ever since our first rocket stove workshop with Tim Barker in Victoria I’ve been secretly coveting a rocket oven to call my own.

So you simply cannot imagine my excitement when in a NZ tipshop (the famous seagull centre in Thames) I came across an old, rusty, yet solidly constructed rocket oven core that had been build almost exactly (yet seemingly independently) to the specs of Tim’s design. Right down to the two sets of baffles to force the exhaust gases to conduct an S path up each side of the oven core, slowing the transit time and allowing more heat transfer (though Tim tells me he’s gone off baffles these days, a story for another time…).

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This oven core would have taken me at least three days of material sourcing and fabricating. So to pick it up, along with some bits of flue, for $10, I was rather stoked. The only obvious issue was the abrupt reduction in the cross-sectional surface area of where the flue exited the top of the oven – an easy fix. The cavity gap or the distance between the two skins through which the flue gasses would travel was also quite small – about 25-30mm, so I wasn’t sure how well the gasses would actually flow, but it certainly seemed like there was scope for a scone or two. I loved that it looked like a bit of rusty junk but that thanks to Tim I had the eyes to see it for the precious jewel that it was.

The thing kept rusting for the next 10 months or so until we found ourselves relatively settled in our new housebus park up. Relatively settled yet ovenless. The time had come to pull it out and get it working.

After another visit to the tip shop I returned with a stand made for working on outboard motors. My mate Pete and I soon grinded (me & Pete’s son Toby) and arc welded (him) this into a perfect little stand for the core. A quick visit to my dad’s shed yielded a length of stainless steel flue pipe long enough to make up the heat riser and the flue out the top of the oven. I even got his permission before nicking off with it.

Within a day we had ourselves a stand and I had riveted on the flue top and bottom. About ten minutes later I’d put it outside and fitted into into a perfectly sized bit of concrete block (which I’ve found falls to bits after a few months – fire bricks or old red bricks much better).


First pass (before insulation). Note the awesome home-made charcoal kiln in background (for my mate Pete’s home-made forge).

I lit it expecting it to fail dismally, or to barely work, and for us to start a long process of tweaking it to get it operational. Imagine my surprise when it started drawing straight away, and within ten minutes was hot enough to bake a tray of scones in no time at all!

The next day we took it to our house bus site and set it up again. I fitted a thermometer (again from the trusty tip shop – from an old bbq lid) in order test it out without any insulation and then to keep testing it as we gradually insulated different bits.


The fist thing I insulated was the oven core by wrangling & riveting an old hot water cylinder shroud. Two finger cuts later we filled it up with pumice and fired it up again (thanks Ciela & Nikka!).

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Next we insulated the riser with a pumice-filled larger flue section which we squished into an oval profile for easier dismantling when we come to move the unit (thanks Brad!).

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Then the burn tunnel and base of the riser which was shedding much heat (Thanks Manda!).

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Meantime whilst I was collecting data it was obvious that what the thermometer on the door said was very different to the actual temperature inside, which was obviously a lot hotter. I estimated by about 50 degreed celsius. So in the name of science I ordered a couple more thermometers, one magnetic one for the outside and one that sits inside the oven exactly where the actual food goes, and both measuring up to a very uncool 400 degrees celsius. The pizzas kept coming and often we’d do several loaves of bread, enough pizzas for ten people, and some sort of desert in one go.


The most impressive timed session I got out of it so far was getting to 180 degrees celsius in 6 minutes, 225 degrees C in 7 minutes, then maxing out at 365 degrees C after 13 minutes. By this point the base of the oven inside was glowing red hot. We were cooking pizzas start to finish in 3 minutes 50 seconds and the only smoke was when we left them in too long. All on a handful of twigs I tell you, a handful of twigs! The thing I really love is that is faster to heat up than a conventional electric or gas oven. So in that sense, twigs aside, it is actually more convenient than its conventional, expense, non-renewable energy gobbling alternative.

Shortly thereafter Tim visited. Things were going quite well till the moment of truth and it came time to light the oven and I got a bit nervous and overloaded it and there was smoke everywhere and flames going the wrong way, and, oh gosh it was not ideal. The student humiliating himself in front of the sensei. Only for a few minutes though – luckily the rocket then started rocketing, the awkward silence broke, and on a few willow twigs we took it up to 355 degrees c at which point the thermometer appeared to jam up. As for the pizzas – oh gosh – delicious.


The apprentice and the sensei enjoying rocket pizza.

And that’s it. I’m done here. What, you want some kind of wrap up? Fine – here you are: Then, dear readers, me, my family, and our brand new rocket oven lived happily ever after. If you would like a similarly happy ending and a much better built oven get yourself along to our next rocket stove/efficient combustion workshop. The end.

Tim Barker explains what rocket combustion is

A short edited clip from our last rocket stove / efficient combustion workshop run by Tim (at Joel’s place).


Rocket Stoves Workshop Report – Part Three – Megan’s mini Rocket Cooker

So this article builds on Parts One and Two and focuses on workshop participant Megan’s construction of a little rocket-stove-powered-cooker she built during our recent The Power of Rocket Stoves workshop with Tim Barker.

Here’s the style of stove Megan was after (from this page)



Ze raw ingredients



Marking out a hole in a 20-litre tin



Tim is the ultimate tinkerer (not to mention self-confessed pyromaniac) and knows all the tricks!



Fitting the lid and flue (insulated with a subsoil/vermiculite mix)…


the insulation

Which looks like this






Light it up and BOOM! Actually as good as this looks it is not how rocket stoves actually work (the combustion and flames are supposed to be down inside the insulated burn chamber). But the flue Megan used was from an old fish and chip shop so this is about 20 years of fat and grease going up!



Cooking up a storm a few days later at the Brunswick Tool Library



So there you have it, all and all a great workshop. Tim’ll be back for another one, don’t worry about that, where we’re keen to try a rocket stove mass heater – any volunteers? Find our next rocket stove workshop here.

Our First-Ever Rocket Stoves Workshop Report – Part Two – The Water heater

So this article builds on the last and shares some photos of our construction of the rocket-stove-powered-hot-water-heater we (mostly) built during our first ever Rocket Stoves workshop with Tim Barker. This unit went up at Yandoit Farm, Victoria, and continues to work beautiful several years later…


Breille & friend getting the base unit in place…









Michael and Tim looking pretty stoked…


See Part Three- Megan’s Mini Rocket Cooker here. Find our next rocket stove workshop here.

Our First-Ever Rocket Stove Workshop Report – Part One – The Oven

Back in May 2014  Tim led our first ever rocket stove workshop on how to build simple rocket stove combustion units for such uses as water heating, ovens, and mass heating. It was a fantastic workshop, hosted by the wonderful Michael and Lisa Jackson at Yandoit Farm, and we wanted to share a few photos and a bit of know-how, here on the oven, with further reports to come on the hot water unit and Megan’s mini-rocket cooker.

Now rocket stoves are super exciting for a few reasons. As noted by Tim:

  1. They offer complete combustion of the wood
  2. They can reach very high temperatures
  3. They can use wood typically considered too small to bother with
  4. They are easily built from common materials.

In other words you can knock these suckers up in a day or two, and they turn twigs into heat way more efficiently than most wood stoves and with way less cost to set up. If you are good at scavenging bits they can cost virtually nothing to build, and when you prune your fruit trees you can get the fuel you need to cook dinner, heat your home, and enjoy a nice hot shower.


Tim kicking off in the Yandoit Farm hayshed.

We started with a little bit of theory (the workshop was about 95% hands-on) with Tim, who got across the key points of difference between rocket combustion and normal combustion. This is all Dan’s possibly muddled recollection, but the main difference is that rocket combustion is complete. Because the compounds released from the wood heated when added to the rocket stove are sucked into the flames, unlike a normal fire, combustion is complete, meaning no smoke. That’s right – smoke mean incomplete combustion, or wasted energy. It was really weird looking down the flue of our first rocket unit at the workshop and feeling the hot air but seeing zero smoke. For we are culturally trained to associate smoke with fire, but with rocket stoves it is true that sometimes when there is no smoke, there is still fire! The second difference is that rocket stoves focus on ensuring complete combustion and only then use the resultant heat. Conventional wood stoves and often use the heat before combustion is complete. The combustion chamber of the rocket stove is heavily insulated to prevent premature heat loss.

Anyway, enough theory, let’s jump to practice, as we did on the Saturday morning.


Whilst Tim showed us how to make the base rocket stove unit from old bricks…


VEG’s Carey and friends (Chris, Brielle & Paul) constituted the poo collection crew. 20 minutes into the workshop and they were shovelling shit!


Which we mixed with subsoil to make a cob mix


With some relatively clean feet..


But not for long!


Work that cob!


Consider it worked.


Relatively unclean feet..


Beautiful cob blobs


And such fun to make!


Securing the base layer


Reshaping the base unit (feeder tube, burn tunnel, and riser)


Flue fitted


Praise to the rocket gods


Blob on the cob


Coming up beautifully!


Here’s one I prepared earlier 🙂


Frame was attached…


A quick chat about the immanent fate of these nice blue barrels…




Revving up the grinder (nice one Megan!)


Brielle aka The Permaculture Terminator


Sparks fly!


Fitting the outer to the inner skin.


Sitting on the frame.



“I am Geoffrey, the badger hunter. Let me tell you the story of my people” – a comment from sculptor Dean.


Pyromaniac Tim getting ready to fire the rocket!


The puff that turns it from a normal fire into a rocket


Ladies and gentlemen, we have lift off…


This is what complete combustion looks like – look mum – no smoke!


Go Team!!!


Tim going for the giant-bong look…


Yandoit farm resident and exceptionally wonderful human being Chris who finished off the stove all by herself in the two weeks after the workshop…


And who would have thought something so rough and ready and functional could be so beauuutiful!


Recycled old supermarket shelves


Finishing off dinner in the oven which we can say lives up to its rep and cooked about seven pizzas and finished off these pies effortlessly and quickly on bugger all wood.


Yeah baby!

See Part Two – the water heater here. Find our next rocket stove workshop here.

Tim’s Creation at 2015 Missoula Rocket Stove Workshop

Twice now‘s Tim Barker has been invited over to the Mecca of Rocket Stoves – Paul Wheaton’s Rocket Stove Lab over in Missoula, USA. Here during his most recent visit he talks us through what he’s been up to – a portable rocket combustion powered field kitchen with a rocket hotplate, oven and water heater all in the one unit.