Water Heater. The Geyser heat-pump water heater connects to the tank of an existing water heater or any similar insulated storage tank but runs more economically than standard electric or gas-fired units, says the manufacturer. The heating element of the existing water heater can be either left on to supplement the heat pump in high-demand situations or turned completely off. The water-heating unit works like any other heat pump, concentrating available heat in the air through a reverse refrigeration process. As a side benefit, the discharge of cooler, drier air may eliminate the need for a dehumidifier in some applications. The unit qualifies for energy tax credits and is available from the manufacturer for $1,400. North Road Technologies, 888/316-2057, northrdt.com.