Heat pumps are a well-established technology for
space heating. The same principle of transferring
heat is at work in heat pump water heaters (HPWHs)
except that the heat they extract from air (indoor,
exhaust or outdoor air) is delivered to water. Some
models come as a complete package including tank
and back-up resistance heating elements while others
work as an adjunct to a conventional water heater.
A HPWH uses about half as much electricity as a
conventional electric resistance water heater.
www.energy.wsu.edu
