A heating unit, characterized in comprising: a heat conductor internally provided with at least one duct for accommodating a PTC heating element, at least one first liquid passage channel, and at least one second liquid passage channel; a first end cover fixedly coupled to one end of the heat conductor, the first end cover being internally provided with a first compartment, a second compartment, an end cover water inlet, and an end cover water outlet, the end cover water inlet being in fluid communication with the first compartment and the first liquid passage channel, and the end cover water outlet being in fluid communication with the second compartment and the second liquid passage channel; a second end cover fixedly coupled to an opposite end of the heat conductor, the first liquid passage channel and the second liquid passage channel being in fluid communication with each other via an internal space within the second end cover so as to form a closed liquid circulation channel; and at least one PTC heating element positioned within the duct of the heat conductor, the PTC heating element having a length longer than that of said heat conductor, characterized by having one end extending out of an end of the duct and a portion of the other end extending out of the other end of the duct; wherein the first end cover includes at least one groove capable of accommodating the portion of the PTC heating element extending out of the duct, the groove extending through an interior of the first end cover and being in communication with an external space; and the second end cover is also provided with at least one opening capable of accommodating the end of the PTC heating element extending out of the duct. a heat conductor internally provided with at least one duct for accommodating a PTC heating element, at least one first liquid passage channel, and at least one second liquid passage channel; a first end cover fixedly coupled to one end of the heat conductor, the first end cover being internally provided with a first compartment, a second compartment, an end cover water inlet, and an end cover water outlet, the end cover water inlet being in fluid communication with the first compartment and the first liquid passage channel, and the end cover water outlet being in fluid communication with the second compartment and the second liquid passage channel; a second end cover fixedly coupled to an opposite end of the heat conductor, the first liquid passage channel and the second liquid passage channel being in fluid communication with each other via an internal space within the second end cover so as to form a closed liquid circulation channel; and at least one PTC heating element positioned within the duct of the heat conductor, the PTC heating element having a length longer than that of said heat conductor, characterized by having one end extending out of an end of the duct and a portion of the other end extending out of the other end of the duct; wherein the first end cover includes at least one groove capable of accommodating the portion of the PTC heating element extending out of the duct, the groove extending through an interior of the first end cover and being in communication with an external space; and the second end cover is also provided with at least one opening capable of accommodating the end of the PTC heating element extending out of the duct.