Rocket stove prototype

Part of the preparation for the summer school programme is to develop prototypes that we’ll be able to share with our future students. Hopefully these will help improving living quality of the inhabitants whose house we will refurbish.

As you might remember, we started working on a Rocket Stove for our production centre Co-Lateral. This experience is part our global agenda: experimenting with sustainable, low-key, methods to heat and insulate houses in southern Europe, over-suffering the mild winters.

What is a Rocket Stove

You might remember our DIY Wood Stove article, published at the beginning of the winter. In this article, we briefly explained the concept of mass, and rocket stove:

“An efficient tweak to the shape of a metal stove results in a rocket stove; its main characteristic is a J-shaped tube. The lowest opening of this J-shape functions as a feeding hole […]. The 90 degree angle in the tube ensures that the heat from the wood in the feeding hole is drawn up into the combustion chamber. When the fire is burning, the combustion chamber sucks fresh air through the feeding hole, prohibiting possibilities of back draft.

Rocket stoves, like rocket mass heaters, are a simple concept heavily customisable. From the starting point design, one can quite easily generate vortex within the riser, to improve the combustion, or foster the creation of a double (or post) combustion, with a second air entrance.”

What we did

Trying to upcycle as most as possible, we wanted to build our prototype with recycled metalic structures, concretely Fire Extinguishers that we got offered by Interfire, and a 47kg propane gas bottle, bought 10€ to a scrap merchant.

Here’s the plan of what we wanted to build:

And see on the right what we did, and more or less how we did it. Cutting, welding, cutting again, welding… then filling space between the gas bottle and the riser with vermiculite.

Please appreciate Hannah Bosland‘s brand new welding skills.

Did it work?

Short answer is yes. We had the deadline of the Actors of Urban Change academy meeting to finish the prototype and see how much it works. Elisabeth Kremer from MitOst wisely suggested us to buy a carbon monoxyde detector, and so did we. We’re happy the alarm never started. We heated the room during the whole meeting, and used it repeatedly for our cinema surpresa and cold working days. There’s no question that the stove can heat around 70m2, using bad quality scrap wood efficiently.

There is though room for improvement:

1- The first issue is the dependency to the operator. This stove is not a low maintenance device. The operator should stick around while it’s burning, to be able to intervene in case of back draft. This happens when the logs don’t fall naturally in the combustion chambers, and the fires goes up in the feeder. One solution is to have a more vertical and maybe wider feeder.

2- A wider chimney, wider and taller, could also improve the draft. Right now the chimney is 12cm diametre, and the riser is around 14cm diametre. We learned in posterior readings that the chimney diametre should be wider than the riser diametre.

3- The fire extinguishers are difficult to work with, and notching cylinder of this diametre (14cm-16cm) with a grinder a serious challenge. We lost a lot of time there, compensating with the welding job. It would have been much easier to work with rectangular tubing, at least for the part of the riser.

4- The metal of the fire extinguisher is quite thin – 3mm -, and it won’t resist long to the heat of the stove, especially in the combustion chamber. A more sustainable solution would be to work out a combustion chamber with refractory materials.

5- If, for us it makes total sense to use scrap wood, material we have in abondance, other fuels can easily be produced recycling paper, used coffee grounds, etc. We’re going to start investigating this with fuel prototypes in the coming future.

More… soon…

Besides rocket stoves for heating purposes, we applied their main principles to other needs. Check out this video and find out about our charring station, a method to char wood effectively and save!

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