The present invention relates to a humidifier (10) for a system for providing a flow of breathable gas to an airway of a patient, wherein the humidifier (10) comprises: a casing (12) configured to contain a liquid reservoir (20); an air inlet (14) which is arranged at the casing (12); an air outlet (16) which is arranged at the casing (12); and a flow passage (18) connecting the air inlet (14) with the air outlet (16), wherein the flow passage (18) is in fluidic communication with the liquid reservoir (20), and wherein the humidifier (10) comprises a heat pipe (24) having a hot end (26) and a cold end (28), wherein the hot end (26) of the heat pipe (24) is arranged outside the casing (12) and the cold end (28) of the heat pipe (24) is arranged in the liquid reservoir (20).