Water heat recycling (also known as drain water heat recovery, greywater heat recovery, or sometimes shower water heat recovery) is the use of a energy recovery heat exchanger technology to recover and reuse hot water heat from various activities such as dish-washing, clothes washing and especially showers. The technology is used to reduce primary energy consumption for domestic water heating. Standard units save up to 60% of the heat energy that is otherwise lost down the drain when using the shower.
The Drain Water Heat Recovery Industry and Manufacturers Association is the international watch dog for the drain water heat recovery industry and has set standards for the manufacturers, representatives and installers of this industry. Members of this association adhere to a strict set of guidelines. Drain Water Heat Recovery Association
The technology was fully recognized in Canada where the federal ecoENERGY retrofit for homes program offered grants for installations and the EnerGuide for New Houses program has energy savings and energy credit calculations that it uses for new home construction. This program has been discontinued and is now closed to new participants. (April 2010).
The retail price for a domestic drain water heat recovery unit ranges from around $500 to $1,000. For a regular household, water heating is the second highest source of energy demand. The savings in energy results in an average payback time for the initial investment of 2–10 years.