Water heat recycling (also known as drain water heat recovery, greywater heat recovery, or sometimes shower water heat recovery) is the use of a heat exchanger to recover energy and reuse heat from drain water from various activities such as dish-washing, clothes washing and especially showers. The technology is used to reduce primary energy consumption for water heating. Standard units save up to 60% of the heat energy that is otherwise lost down the drain when using the shower.
The technology is fully recognized in Canada and USA by LEED for homes, Energy Star for New Homes Canada.
Typical retail price for a domestic drain water heat recovery unit ranges from around $400 to $1,000. For a regular household, water heating is usually the second highest source of energy demand. The energy savings results in an average payback time for the initial investment of 2–10 years according to Natural Resources Canada, Canadian Center for Housing Technology and US DOE.