I just built an off-grid cabin, and built heat reclamation into our plumbing in multiple locations, as it seemed silly not to. Currently we’re using butane for

I just built an off-grid cabin, and built heat reclamation into our plumbing in multiple locations, as it seemed silly not to. Currently we’re using butane for our hot water, although I’m switching to biogas in the spring - the first stage of reclamation is a simple loop of hot water line around an insulated hutch in which the gas bottle lives - keeps it warm, as butane is useless in cold weather. The second stage of reclamation is exactly what he proposes - our cold water line comes in, spirals around the waste water line for about 5/40 meters of respective length, in an insulated sleeve, before hitting the boiler. Our input water is often barely above freezing - it’s the difference between having a cold/lukewarm shower and a scaldingly hot one.