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?
Rocket mass heater
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.
A wood heater with an insulated burning chamber that makes a very hot, clean fire, and a long bench of earth or stone that the hot gases run through before leaving by the chimney. The bench soaks up the heat and gives it off for many hours. A short fire warms the house long after it is out, on little wood.
20-30+ years for the combustion core and thermal-mass bench if built to a proven design; firebrick/refractory components may need earlier replacement
Embodied carbon
Low
Space / material use
Medium
Output timing
On-demand/controllable
Skill to repair
Basic
Regulation (FR example)
Flue installation follows DTU 24.1. Chimney sweeping is compulsory (typically once or twice a year) under the departmental sanitary regulation, and insurers generally require proof. Some communes restrict wood burning under an air-quality plan.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Rocket mass 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: 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.
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.
Gas boiler (condensing) 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.
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.