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?
Gas water heater
Needs the grid
One of 7 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
A gas supply or room for a tank, and a compliant flue route
Heats domestic hot water by burning gas, either on demand as the tap runs or into a stored cylinder. On-demand avoids keeping a tank hot for nothing; a cylinder copes better with several draws at once.
Build it
This solution is not buildable as a DIY project.
Cost
Low
Upkeep
Occasional
Skill to build
Specialist
Lifespan
Long; scale in hard water shortens it more than age does
Embodied carbon
Medium
Space / material use
Low
Output timing
On-demand/controllable
Skill to repair
Specialist
Regulation (FR example)
Gas appliances must be installed and commissioned by a qualified fitter, and a French installation is subject to periodic inspection.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Gas water heater (This page) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Specialist · Upkeep: Light · Change to daily life: None · Works without the grid: No Choose it if you are on the gas mains and want hot water on demand, without keeping a tank hot.
Thermosiphon solar water heater 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: Occasional · Works without the grid: Yes Choose it if you want solar hot water kept in its own insulated tank, with no pump.
Compost-coil water pre-heater Can I use it? Not in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Basic · Upkeep: Light · Change to daily life: Occasional · Works without the grid: Yes Choose it if you already keep a big compost heap and want it to pre-heat your water.
Electric resistive water heater (cumulus) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: Light · Change to daily life: None · Works without the grid: No Choose it if you want the cheapest heater to buy, with parts you can replace yourself.
Batch solar water heater (integrated collector-storage) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Daily · Works without the grid: Yes Choose it if you want the simplest solar hot water, panel and tank in one box.
Wood-stove flue water heater (thermosiphon coil) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: Light · Change to daily life: Daily · Works without the grid: Yes Choose it if you already run a wood stove and want hot water from it in winter at no extra fuel.
Heat-pump water heater (chauffe-eau thermodynamique) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: High · Skill to build: Specialist · Upkeep: Heavy · Change to daily life: None · Works without the grid: No Choose it if you want electric hot water for a third of the power, and have an unheated room for it.
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.