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?
Heat pump (air- or ground-source), reversible mode
Needs the grid
One of 6 ways to meet this need. Cost, carbon, footprint and rankings are relative to other solutions for the same need, not absolute.
A heat pump that can run in reverse, pumping heat out of the house in summer as well as in during winter. One machine heats and cools, so there is no need for a separate air conditioner. It cools no more efficiently than an air conditioner would; the saving is in not buying a second machine.
Build it
This solution is not buildable as a DIY project.
Cost
High
Upkeep
Seasonal
Skill to build
Specialist
Lifespan
Same physical unit as the heat pump: 10-15 years typical, up to 20 for well-maintained units
Levels are relative to the other options for this need, not absolute. Fewer dots is lighter.
Heat pump (air- or ground-source), reversible mode (This page) 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 already need a heat pump for winter and want the same machine to cool.
Night-flush cooling 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: Yes Choose it if your nights are cool and you want to cool the house for free.
Evaporative cooling 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 your summers are dry and you want cheap cooling.
Night-sky radiative cooling 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: None · Works without the grid: No Choose it if your summer nights are usually clear and you want to cool with the night sky.
Ceiling fan 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: None · Works without the grid: No Choose it if you want to feel cooler where you sit, for a fraction of a cooling machine’s power.
Whole-house fan 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: Occasional · Works without the grid: No Choose it if you want night cooling that works even on still nights.
Sources
Heat pump lifespan industry sources (permies.com heater-lifespan wiki; general HVAC industry consensus)
Limitations of this page
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.