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?
Mechanical ventilation with heat recovery (MVHR)
Needs the grid
One of 2 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
An airtight envelope, MVHR loses most of its value without it
A fan unit that pulls stale air out of the house and brings fresh air in, passing both streams through a heat exchanger. The outgoing warm air heats the incoming cold air without mixing with it. The house gets fresh air all the time while keeping most of its heat. It can be a factory unit installed by a professional, or built at home: one whole-house home build, with a plastic-plate exchanger and small 12 V fans run by a microcontroller, kept 84% of the heat over four months for about €1,600 with its ducts. The home build is the version rated here; it takes about two weeks, some electronics and a little programming.
15-30 years for the core unit; filters need replacement every 3-6 months, fans/motors are the usual mid-life failure point
Embodied carbon
Medium
Space / material use
Low
Output timing
On-demand/controllable
Skill to repair
Intermediate
Regulation (FR example)
Dwellings must have general and permanent ventilation (arrete du 24 mars 1982, modifie). Mechanical ventilation is the usual way of meeting it in an airtight building.
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Mechanical ventilation with heat recovery (MVHR) (This page) 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: None · Works without the grid: No Choose it if you want the whole house ventilated by one central unit that keeps most of the heat.
Decentralised single-room heat-recovery ventilators 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: None · Works without the grid: No Choose it if you want heat-recovery ventilation room by room, without running ducts.
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.