Top-lit updraft gasifier: pyrolyzes wood or pellets in a low-oxygen chamber to release combustible syngas, then burns that gas in a secondary combustion zone above, roughly 30-45% thermal efficiency well-built, against 10-15% for an open three-stone fire, per the source's own comparative figures (citing a specialist, Dr. Paul Anderson, and a third-party comparative cookstove report). Produces reusable char as a byproduct, a direct input to the biochar entry. Buildable from tin cans for near-zero cost, though a tin-can build has a short working life; a stainless-steel version lasts longer.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.