Rocket Oven

For over a decade I have studied, doodled and dreamed of making a rocket-stove oven.  For the last few months I have been researching and planning to actually build one – at the Oxford City Farm.

It will be next to an outdoor kitchen and may be used less than once a week, but occasionally will feed over a hundred visitors over several hours, so it has a large oven.  It includes a ‘batch-box‘ allowing a large amount of wood to be burned, and a heated bench to warm up those waiting for their pizza.

Here are our latest drawings and plans:

 

View from inside the kitchen:

The bulk of the structure is made from red bricks.  The hot-plate (under the kettle) will be a sheet of stainless steel, probably 5-6mm thick, hopefully from our local salvage yard.  The oven itself is made from half an oil drum, also from salvage – 60cm in diameter and 45cm deep – enough for 4 or 5 shelves inside for baking batches of large pizza. This is a ‘white oven’ which means the contents never gets direct contact with the smoke and hot gasses. Most pizza ovens are ‘black ovens’ where the smoke comes into and around the food adding a ‘woodsmoke’ flavour but also risking possible contamination from additives in ‘found wood’. We have some heavy duty slabs of kiln shelving from an old kiln which might be very useful to make the roof of the firebox (under the oven) and maybe the serving surface.

The fire-box (where the wood is burned) under the oven will be made of fire-bricks.  So will the riser (where the burning wood gases roar upwards in an inner chimney creating the ‘rocket’ sound), under the kettle.  See plan diagram below for more on this.

 

View from outside the kitchen

The seat of the heated bench will probably be made from paving slabs, with cushions and blankets brought out when people are around.  So while you wait for your pizza, you can warm yourself bottom-up!  We might cover some of the brick-work with cob, which would add more insulation and look prettier, and be made weather-proof with linseed oil.

 

Plan view

This drawing shows the clever bit – the ‘choke‘.  When the fire is first started we will want the chimney to ‘draw‘ the heat and smoke through the stove’s bell structure.  By pulling the choke out, the hot air is allowed the ‘short route‘ of going straight up the chimney, bypassing the heated bench.  But once the fire is raging and we want to divert the heat to the bench we push the choke back in which opens up the ‘long route‘ for the hot air to instead move in and through the heated bench passing its heat to those bricks and warming our guests from below.  At the same time the paddle has closed off the ‘short route’ preventing the hot air from going straight to the chimney.  There may also be times when we want to cook without heating the bench.

 

Inside the rocket stove pizza-oven

This tentative plan shows two side views and a plan view at the height of the oven.  Wood is placed in the fire-box and lit.  Primary burn happens there, heating the air in the insulated riser – the inner chimney.  The doorway from the fire-box to the riser is partly restricted which encourages turbulence for a hotter and cleaner burn.  The hot gasses in the riser are now engaged in a secondary burn.  They race up the riser into the bell sending a lot of heat up into the hot-plate under the kettle. Also much of these hot gases are now swirling around the bell encircling the drum of the oven, heating up the air inside, cooking our pizzas!  Depending on the position of the choke, the cooler air in the bell will be pulled out, either into the heated bench and then up the main chimney, or directly up the chimney.  Most of the particulates in the wood smoke will be burned up completely in the bell, so any smoke coming out of the chimney will be quite clean.  Most of the heat from the burn will be passed on to the hot-plate, the oven and the heated-bench.

 

Covering the hot plate

The hot-plate will be about 130cm above the ground.  So small children who somehow get into the kitchen will not be able to reach it.  We will also have three optional insulating covers for the hot-plate to make it even safer.  And if we want to cook without also heating a kettle (unlikely in the UK) these covers will keep more heat inside the bell.  These covers will be made from the kiln shelves.  On top of these we will have a wooden serving board that turns the oven top into a work surface, adding even more insulation.

 

If you are an experienced rocket-stove builder we would be very grateful for your opinion.  If you have any questions, corrections or suggestions about this project,
please contact me using the form on the ABOUT page.  Thanks.

 

We are very grateful to the pioneering work of many people who developed the rocket-stove over the last 50 years.  They include Ianto Evans, Donkey’s forums on rocket stoves, Peter van den Burg, Paul Wheaton and the folks at Permies – forums on rocket stoves and Matt Walker.