A condenser is a unit that collects the steam that normally is vented from the dishwasher and condensates it. Cold water is circulated through a radiator type device and hot vapours are drawn though by a fan. In many cases the water from the condenser is used for the final rinse process as it is slightly pre-heated. A heat recovery unit is similar to a condenser but with a larger heat exchanger and the heat that is transferred to the water is used to pre-heat final rinse water. A heat pump is a heat recovery unit that uses a refrigerant to remove all excessive heat from the machine and re-use for the final rinse. In most cases a heat recovery unit eliminates the need for direct connection to external ducting. However, the requirement for adequate room ventilation according to building codes still applies.