A south-facing wall-mounted box (tested at 2m2) with a black-slate absorber behind glazing; convective baffles route room air drawn in low, heated by the sun, and returned high by thermosiphon, no fan, no electricity. Source-tested performance: a 5-7C room-temperature rise for a 10-15m2 room in French winter conditions. A wax-thermostat-driven damper opens the circulation automatically only once the collector exceeds 25C and closes it below that, entirely passively. A summer vent ('trappe ete') repurposes the same unit as passive stack ventilation, exhausting warm room air outward instead of returning it. Complements rather than duplicates the window-based passive solar gain entries: those capture gain through glazing directly into the room, this is a dedicated, adjustable-output collector that can be sized and placed independent of window layout.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
South-facing wall area with two through-wall penetrations (low intake, high return) into the conditioned space
No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.