Passive
One of 3 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
None beyond a way of heating water
A sealable container of hot water in a textile cover, held against the body. It works indoors and out, needs nothing but water that has already been heated, and is the cheapest way there is to stay warm in a cool room. Widely dismissed as an invalid's item rather than a heating strategy, which is a cultural judgement rather than a technical one.
Compare building and maintaining complexity, as well as efficiency where possible.
| Solution | Build skill | Upkeep burden | Efficiency |
|---|---|---|---|
| Hot water bottle | None | 2 | N/A |
| Electrically heated table (kotatsu) | Basic | 4 | N/A |
| Solar-powered foot stove (heat cube) | Intermediate | 3 | N/A |
Build skill and upkeep burden are proxies (lower burden = simpler to maintain); the efficiency column is this sub-function’s ranking, 1 = best. “N/A” where an axis isn’t rated here.
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.