Passive heat exchanger around a shower/sink drain preheats incoming cold water using outgoing warm greywater, no pump, feeds directly into domestic water heating.
Note: Cost, carbon and footprint are rated against the other options for this same need, not in absolute terms.
A vertical drain run accessible for the exchanger to wrap or replace a section of pipe
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.