 In systems using refrigerant, this working fluid can also be used to transfer heat a considerable distance, though this can become impractical because of increased risk of expensive refrigerant leakage.When large amounts of heat are to be transferred, water is typically used, often supplemented with antifreeze, corrosion inhibitors, and other additives.A common source or sink for heat in smaller installations is the outside air, as used by an air-source heat pump.