Some of this stuff is only not worth it because it's insanely overpriced. DWHR is a fine example of this: the device is just a couple feet of double walled co

Some of this stuff is only not worth it because it's insanely overpriced. DWHR is a fine example of this: the device is just a couple feet of double walled copper pipe. It should be dirt cheap, but instead they sell for $800. The real limit for DWHR is that you need a vertical drop to get sheet flow, a horizontal section would be much less effective. Also there is a moderate plumbing complication from the fact that your 'cold' water in the shower also needs to be sourced from the DWHR to not have a massive heat leak. With the high price of the DWHR and the plumbing complications it'll never pay for itself except with the highest shower usage in the coldest climates. That said, cost shouldn't be the only consideration. Even disregarding environmental concerns a building that is more passively efficient will work better during outages/energy shortages.