A wide variety of water heaters use primarily gas or electricity to heat water for cleaning, washing, bathing, and showers. Electric resistance water heaters use metal coils like an electric coffee pot or stove top which heat surrounding water. Newer electric water heaters use heat pumps which gather heat from a source like the surrounding air, compress it and concentrate the heat in a transfer medium (“refrigerant”) so that it will heat water passing through a heat exchanger. Since heat pump water heaters gather heat from the environment, they can produce multiple units of heat from a single unit of electricity. An electric resistance water heater can produce no more than one unit of heat from one unit of electricity.