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 boiler (condensing)
Needs the grid
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
A gas supply or room for a tank, and a compliant flue route
A boiler that burns gas to heat water for radiators or underfloor heating, and recovers some of the heat that would otherwise go up the flue. It is the usual way French homes are heated, and gives steady heat on demand, but it burns fossil fuel and depends on the gas supply.
Build it
This solution is not buildable as a DIY project.
Cost
Medium
Upkeep
Occasional
Skill to build
Specialist
Lifespan
Long, given the annual service it is legally required to have
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 boiler (condensing) (This page) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · 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 steady heat on demand from a system every installer knows.
Wood stove / mass heater Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Basic · Upkeep: Heavy · Change to daily life: Daily · Works without the grid: Yes Choose it if you want a familiar wood fire that heats the house without electricity, from local wood.
Heat pump (air- or ground-source) 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 have reliable electricity and want efficient heat with no fuel to handle.
Rocket mass heater Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Low · Skill to build: Intermediate · Upkeep: Heavy · Change to daily life: Daily · Works without the grid: Yes Choose it if you want the most heat from the least wood, stored in a bench for hours.
Gravity-fed pellet stove (no electricity) Can I use it? Works in a flat · No rebuilding needed What does it cost me? Upfront cost: Medium · Skill to build: Intermediate · Upkeep: Heavy · Change to daily life: Daily · Works without the grid: Yes Choose it if you want steady pellet heat that keeps going in a power cut.
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.