This is a rocket stove joined to a mass of earth, clay and stone that soaks up the heat. It burns small sticks hot and clean. The hot exhaust runs through a thick clay-and-stone bench before it leaves, and the bench gives off the heat for hours. Everything below can be gathered or made on site; no metal is needed.
This page is the design reference for the stove in the one-person shelter between three trees: how it works and every size. The step-by-step instructions are in Instructions, where each job lists the tools, materials and skills it needs and links to the jobs it relies on. The sizes there are filled in from the same design, so the two cannot disagree.
feed tube ──► burn tunnel ──► heat riser (insulated chimney) ──► dome (hot exhaust drops)
│
chimney ◄── channel through the bench (heat goes into the mass) ◄──┘
The riser is insulated, so it gets very hot and pulls hard, like a turbo. That strong pull drives the exhaust through the long bench channel.
The feed tube, burn tunnel, riser and all the channels have the same cross-section, 11 × 11 cm, all the way through. The other sizes below were chosen within the allowed ranges so the stove keeps the most heat and still starts well from cold and with damp wood.
| Part | Size | Allowed range |
|---|---|---|
| Feed tube (vertical, sticks drop in) | 11 × 11 cm, 30 cm tall | about 30 cm tall |
| Burn tunnel (horizontal) | 11 × 11 cm, 40 cm long | 30–40 cm long |
| Heat riser | 11 × 11 cm inside, 110 cm tall | 80–120 cm, and at least twice the tunnel length |
| Riser insulation | 8 cm of light clay around a 3 cm refractory wall | 8–10 cm |
| Gap from riser top to cooktop | 6 cm | 5–8 cm |
| Gap from riser to dome wall | 5 cm | about 5 cm |
| Bench channel | 11 × 11 cm, about 3.9 m, 2 bends | up to 3–4 m, as few bends as you can |
| Mass over the channel | 20 cm | 15–25 cm |
| Chimney | 11 × 11 cm, top 2.35 m above the floor, stone and cob all the way up | top at least 60 cm above the riser top and 60 cm above the roof beside it |
If you undersize any section, it will choke the whole system and smoke will come out of the feed tube.
They are all inside measurements: the open space the fire and gas move through. Wall thickness goes on the outside of these numbers, so the formers you pack clay around should be these sizes.
| Dimension | Measured |
|---|---|
| 11 × 11 cm cross-sections (feed tube, burn tunnel, riser, channel, chimney) | Inside wall to inside wall, the clear opening |
| Feed tube height (30 cm) | From the burn tunnel floor up to the top of the feed opening |
| Burn tunnel length (40 cm) | Along the inside floor, from the inside of the feed tube's back wall to the inside of the riser's far wall |
| Riser height (110 cm) | From the burn tunnel floor to the top lip of the riser |
| Riser-top-to-cooktop gap (6 cm) | Clear air gap from the riser's top lip to the underside of the cooktop stone |
| Riser-to-dome-wall gap (5 cm) | Clear air gap from the outside of the riser to the inside of the dome wall |
| Bench mass over channel (20 cm) | From the top of the channel's inside to the bench surface |
| Chimney top (2.35 m) | From the shelter floor, which is level with the burn tunnel floor |
Measuring the riser from the tunnel floor and the tunnel along its inside floor keeps the riser-to-tunnel ratio honest.
If a wall ends up bumpy, make sure the narrowest point is still at least 11 × 11 cm. One pinch point chokes the draft as badly as undersizing the whole run. Cob also shrinks a little as it dries, so it's fine to make the formers about 1 cm oversize.
Each link opens the instruction, with what it needs and the jobs it calls. They run in this order within the season plan; the season schedule shows when each one falls.
The mixes (cob, refractory mix, light clay, mortar, slip and plaster) are instructions of their own, called where they are needed. The fish weir is in Build the fish weir.