Some machines use a single boiler kept at steaming temperature, but water for brewing is passed through a heat exchanger, taking some heat from the steam without rising to the same temperature. This is found in many mid-range machines. There is some controversy as to the temperature stability of the brewing water, since it is indirectly converted from steaming temperature to brewing temperature, rather than kept at a brewing temperature.
DOUBLE CIRCULATION It adds to the version 1 a very practical solution for filling the water tank without moving the cups. It adds a touch of class with all-wood finishes. Insulated boiler and pump pressure regulation.