Abstract: A heat exchanger device, comprising a first heat exchanger for evaporation of liquid natural gas (LNG), and a second heat exchanger for superheating of gaseous natural gas (NG). The heat exchangers (1) are arranged for heating these fluids by means of a heating medium and have an outlet which is connected to a mixing device (20) for mixing the heated fluids with the corresponding unheated fluids. According to the invention the heat exchangers (1) comprise a common housing (2), in which there are provided separate passages (7, 8) for the fluids. The mixing device (2) constitutes a unit together with the housing (2) and has a single mixing chamber (23) with one single fluid outlet (30). In separate passages (7, 8) there are provided valves (10, 26) and (13, 28) respectively for the supply of LNG or NG in the housing (1) and the mixing chamber (23).