As a highly energy-efficient alternative to the traditional electric or gas water heater, our unique system saves money, reduces greenhouse gas emissions and eliminates the production of carbon monoxide. The SANCO₂ heat pump water heater system consists of two parts. The Heat Pump Unit, where the hot water is produced, using the CO2 refrigerant to extract heat from the ambient air, and the insulated Storage Tank, available in 43, 83, 119, 200, 285, 360, 455 and 505 Gallon Sizes, where the hot water is stored. Installation of the unit is simple, with two water pipes connecting the tank to the outdoor heat pump. SANCO₂. Hot Water, Naturally.