Rocket Stoves

1. Rocket Stoves

Rocket stoves are a set of principles designed for improving combustion efficiency and heat transfer efficiency: Since hotter fires burn more efficiently, the combustion chambers in rocket stoves are insulated and no mass is used around the pot in order to transfer the heat into the pot and not into the stove itself. For a fire to burn hot, it also needs good air draft, what you improve by a small opening in the feed tube, a shelf in the opening and a grate under the fire. For optimal heat transfer into the pot, you will need a “skirt” around to pot to force the hot gases to scrape the pot. Correct proportions are recommendable to maintain the cross sectional area throughout the stove for best efficiency. Following these principles you create extremely hot fires that roar and give them the “rocket” in their name.

Since you follow a set of principles, you can build a stove depending on your personal and community needs. There are simple stoves for one family sized pot, there are institutional Rocket Stoves for commercial or community kitchens, there are stoves for multiple pots with different temperatures along the gas tunnel, there are griddle stoves for frying and baking corn tortillas. We build Rocket Stoves for one-three pots and stoves with a griddle, the so-called Justastove, which as become very popular in Central America.

Example of Material List for Multi-Pot Rocket Stove:

  • Foundation: stones, gravel and maybe pvc or similar for moister barrier
  • Bricks, adobes or cob for stove base
  • Combustion chamber: around 12 cm pipe. It is possible to construct this out of other things as well: bricks, clay, tiles etc.
  • Chimney: tin cans/ metal pipe
  • A metal plate for stove top. The best is a thicker piece of metal. With metal, we will need an angle grinder unless there are already pot holes in it.
  • This stove can also be entirely made of an insulated earth material, sawdust/clay for example
  • The pots used for cooking will need to be there to design the stove dimensions

Example of Material List for Rocket Stove with a griddle:

  • Cooking griddle (rolled steel): 4-8mm thick, 40x80cm with 2,5cm “lip” and ideally handles
  • Combustion chamber: bricks or thick metal
  • Three buckets (20l) of insulative material: wood ash, pumice rock, vermiculite to fill front half of the stove body 13” by 12” by 14” (in metric: 33 by 30,5 by 35,60cm).
  • 2 wheel barrows full of clay/sand mortar for constructing the stove body (3 clay:1sand)
  • 3 buckets (20 liters) of dry sand or earth to fill the rear half of stove body
  • clay/sand for finish plaster or aliz clay paint.
  • 2” or 10cm tin can with plastic or metal lid
  • Tools: shovel, wheelbarrow, 1-meter carpenter’s level, aviation snips, hacksaw, square, hammer, trowel.

2. Rocket Mass Heaters

”It is extremely efficient, reaching 90 percent combustion, and almost all the heat is then stored in the cob mass bench, to be slowly released over days”!

—Ianto Evans, inventor of the Rocket Mass Heater

A rocket mass heater is a space heating system developed from the rocket stove principles and the masonry heater. Wood is gravity fed into a “J-shaped” combustion chamber, from where the hot gases enter a heavily insulated metal or fire-brick vertical secondary combustion chamber, the exhaust from which then passes along horizontal metal ducting embedded within a massive cob thermal storage, what can take shape of a bench or a bed.

The thermal store is large enough to retain heat for many hours and typically forms part of the structure of the building. Rocket Mass Heaters are usually self-built and be aware that they are not yet recognized by all building codes, which regulate the design and construction of heating systems within buildings!

Example of Material List for Rocket Mass Heater:

  • Bricks (Depending on if the heat riser is made out brick or steel):
  • 65 if making heat riser with brick, 45 with steel heat riser
  • Barrel (200 liter barrels are the most common ones and easiest to find)
  • Insulation container: Sheet metal or skinnier barrel
  • Insulation for stove parts: Pumice, wood ash, perlite, vermiculite, leka or clay-sawdust mix.
  • For manifold (connection between stove and ducts in bed): some metal mesh, bricks also work
  • Pipes/smoke ducts: metal pipes, 15-20 cm diameter.
  • Enough clay and sand (+straw) for the construction
  • Rocks work as a great infill and shorten the construction time
  • Large Bucket or small barrel for feedtube
  • Chimney materials: pipe and cap
  • Building tools: buckets, shovels, trowel, chisel for bricks, wheelbarrow and an angle grinder with disk for metal.
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