Saturday 31 May 2014

Building a Rocket Stove

For a number of years I have spied the design of a number of different rocket stoves. For the confused amongst you, it is a simple, highly efficient (if done correctly) way of burning wood to cook food. These were mainly devised to be used in refuge situations where the supply of an energy source would be scarce. The principal is simple. An inlet chamber where your fuel goes, has a slot underneath it to allow the flow of air under the fuel and into the flue/chimney. This allows for a more intense burn, less unburnt products of combustion (smoke) and more efficient use of small amounts of fuel.

That's the theory. The engineers amongst us could do a fantastic job of ensuring all the hot gases were properly used, just for the record, we were not going for that level of efficiency. We wanted a decent height, fairly efficient stove that we could top with a griddle tray providing an out door cooking area. You see we cook indoors on a wood burning Esse, like an Arga, but the thing consumes copious amounts of wood to not only cook our food, but also heat the hot water tank and run the houses heating system. In the middle of summer, we wanted to cook a little more"Al Fresco".
Firstly we scrounged some free cinder blocks from a neighbour (like a proper gift economy, we let her use our field for her horses, she bungs us a few unused cinder blocks) and chose a spot to position them.  In this photo above Danny is using a tool that neither me nor my brother utilise in our other projects, but Danny being the perfectionist wanted a flat bottom.
Two layers up, and still insisting on using that level (?!), we fill the blocks with earth and earth up around the sides for additional support.  We will over the coming months properly encase all of this in a nice cob jacket, but that requires locating a good supply of clay, which we think we MAY have.
Pile up your blocks to check the height and we placed the griddle on top to see what clearance we had.  The hot gases will come up right under the griddle and flow out either way heating the entire surface.
This picture above shows the combustion chamber in the centre, the two outside chambers were filled with perlite.
Looking down at the top of the stove we filled all the cells around and on top of the combustion chamber and flue with perlite.  This material is a light weight, low heat transfer material that means that the heat is not stripped from the chamber aiding the efficient burning of all the materials.
A small cap of rough cob to protect the perlite from the weather and we are getting closer now to firing up the stove for the first time.
I used the metal door on an old rabbit hutch and bent it over a chair to provide our fuel platform, remember it's critical to have the air gap underneath!
Added some thin twigs to start it off and eventually after 15-20 minutes added some slightly large pieces of wood.
You have this lovely little combustion chamber heating the griddle on top.  Meaning you can cook a lot flippin quicker then you could indoors!
Danny adding some fuel on this one and you can see on top a small frying pan with mini hotdogs for Freya and a large pot of Chilli for the rest of us.
This is the location of the stove and you can see the different "grades" of wood ready to be used in it.  I love it.  It works exactly as you could hope it would.  It was built with materials found or borrowed with the exception of the perlite which you can buy very cheaply online (about £30 for 100 kg, which would have insulated two our-size rocket stoves.  I will post again once we have given the stove a nice cob jacket.