Kudos to Alex Wilson for his recent GreenSpec article on drain water heat recovery. This is one of those energy-saving ideas been around for a while, but is a bit of a sleeper — it hasn’t gotten as much attention as it deserves. I’m a fan and have been including this topic for the last couple of years in the Zero Net Energy Homes classes I teach for utility customers in California. Drain water heat recovery is appealing for its simplicity: as warm water goes down the drain (from showers, etc.), the heat is recaptured via a copper pipe spiral-wrapped around the drain line. The photo here shows an installation by Larry Weingarten, a water heating expert in California.