Glossary · Hot water
Drain-water heat recovery (DWHR)
Also called: greywater heat recovery · shower heat recovery · drain heat recovery
A copper section of the main drain that uses warm shower water going down the drain to preheat the cold water coming in.
What it means
Cold water is routed through coils wrapped around a vertical drain stack, and heat passes through the copper while the two streams never mix. It has no moving parts and works best when warm water is going down the drain while fresh water is drawn at the same time, mostly during showers.
Why it matters in an audit
It's an easy add-on during plumbing renovations or new construction and trims water-heating energy for the life of the house.
In Canada
NRCan keeps a searchable list of tested drain-water heat recovery units.