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?
Outdoor air brought into the house to replace stale air. Ventilation of every kind starts here, and in winter a heat exchanger can warm it with the air going out.
It arrives on the site on its own. Nothing in the catalogue makes it. In the builder you add it as “Fresh air”.