While a refrigerator takes away heat from inside a compartment and releases it into the surrounding area, a standalone air-source heat pump water heater draws heat from the surrounding air and discharges it – at a higher temperature – into a tank for water heating. You have the choice to purchase a standalone heat pump water heating system as an integrated unit that comes with a built-in water storage tank and backup resistance heating elements. Additionally, it is feasible to retrofit a heat pump to work in combination with an existing conventional storage water heater.