Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Hot water bottle
Passive
One of 5 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
What your site needs
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.
2-5 years for a rubber bottle, which perishes and should be replaced on a schedule rather than when it fails; indefinitely for a stoneware or metal one
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Hot water bottle (This page) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: None · Upkeep: Light · Change to daily life: Daily · Works without the grid: Yes Choose it if you want the cheapest warmth there is, for one person, indoors or out.
Electrically heated table (kotatsu) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Daily · Works without the grid: No Choose it if you want to keep everyone warm around one table while the room stays cool.
Solar-powered foot stove (heat cube) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Daily · Works without the grid: Yes Choose it if you want evening warmth from the day’s sun, with no fire.
Box-bed with thermal curtain Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: None · Change to daily life: Way of living · Works without the grid: Yes Choose it if you want to sleep warm, in the dark and quiet, in an unheated bedroom.
Insulating furniture (hooded chair, folding screen) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: None · Change to daily life: Occasional · Works without the grid: Yes Choose it if you want to stay warm where you sit, sheltered from cold walls and draughts.
We don’t list sizing or quantities, as the yield of each technique depends on the quality of its build. The catalogue compares options but doesn’t dimension them. Regulatory notes are indicative, with a French example, and need to be confirmed locally.