The present invention is related to a dishwashing machine (100) comprising a washing unit (1), a rinsing unit (2) and a heat pump circuit (3) for heating water to be used in said washing unit (1) and/or in said rinsing unit (2), wherein a washing chamber (10) and a rinsing chamber (20) are defined in said washing unit (1) and in said rinsing unit (2), respectively; it further comprises a suction device (4) mixing an air flow (A) drawn from an environment in which said dishwashing machine (100) is installed and a vapour flow (V) exiting from said rinsing unit (2) and/or from said washing unit (1), said suction device (4) being connected to a heat pump heat exchange unit (30) of said heat pump circuit (3) for heating a working fluid flowing in said heat pump circuit (3) by a mixed flow (M) of said air flow (A) and said vapour flow (V). The invention also relates to a method for operating a dishwashing machine (100) including a washing unit (1), a rinsing unit (2) and a heat pump circuit (3) for heating water to be used in said washing unit (1) and/or in said rinsing unit (2), wherein a washing chamber (10) and a rinsing chamber (20) are defined in said washing unit (1) and in said rinsing unit (2), respectively, said method comprising: mixing an air flow (A) from an environment in which the dishwashing machine (100) is installed with a vapour flow (V) exiting from said washing unit (1) and/or said rinsing unit (2); heating a flow of working fluid in said heat pump circuit (3) by a mixed flow (M) formed by said mixing said air flow (A) and said vapour flow (V).