A heating unit, comprising: a heat conductor (a1), internally provided with at least one duct (a11) for accommodating a PTC heating element (a2), and at least one liquid passage channel (a12); a first end cover (a3) fixedly coupled to one end of the heat conductor (a1), the first end cover (a3) being provided with an end cover water inlet (a31) in fluid communication with one end of the liquid passage channel (a12); a second end cover (a4) fixedly coupled to an opposite end of the heat conductor (a1), the second end cover (a4) being provided with an end cover water outlet (a41) in fluid communication with the other end of the liquid passage channel (a12); and at least one PTC heating element (a2) positioned within the duct (a11) of the heat conductor (a1), the PTC heating element (a2) having a length longer than that of the heat conductor (a1) and having at least one end extending out of the duct (a11) characterized in that : the first end cover (a3) is provided with at least one first groove (a32) capable of accommodating the portion of the PTC heating element (a2) extending out of the duct (a11), the first groove (a32) being in communication with an external space; and/or the second end cover (a4) comprises at least one second groove (a42) capable of accommodating the portion of the PTC heating element (a2) extending out of the duct (a11), the second groove (a42) being also in communication with the external space. a heat conductor (a1), internally provided with at least one duct (a11) for accommodating a PTC heating element (a2), and at least one liquid passage channel (a12); a first end cover (a3) fixedly coupled to one end of the heat conductor (a1), the first end cover (a3) being provided with an end cover water inlet (a31) in fluid communication with one end of the liquid passage channel (a12); a second end cover (a4) fixedly coupled to an opposite end of the heat conductor (a1), the second end cover (a4) being provided with an end cover water outlet (a41) in fluid communication with the other end of the liquid passage channel (a12); and at least one PTC heating element (a2) positioned within the duct (a11) of the heat conductor (a1), the PTC heating element (a2) having a length longer than that of the heat conductor (a1) and having at least one end extending out of the duct (a11) characterized in that : the first end cover (a3) is provided with at least one first groove (a32) capable of accommodating the portion of the PTC heating element (a2) extending out of the duct (a11), the first groove (a32) being in communication with an external space; and/or the second end cover (a4) comprises at least one second groove (a42) capable of accommodating the portion of the PTC heating element (a2) extending out of the duct (a11), the second groove (a42) being also in communication with the external space. the first end cover (a3) is provided with at least one first groove (a32) capable of accommodating the portion of the PTC heating element (a2) extending out of the duct (a11), the first groove (a32) being in communication with an external space; and/or the second end cover (a4) comprises at least one second groove (a42) capable of accommodating the portion of the PTC heating element (a2) extending out of the duct (a11), the second groove (a42) being also in communication with the external space. <EOS>