An improved, pumpless respirator (ventilator) humidifier is provided with a water refilling device (1, 2) and with an electrically heated evaporator (5). The evaporator (5) has a tubular housing, which is filled with a porous sintered material. A front side of the housing is in liquid connection with the automatic water refilling device (1, 2) and the other front side is in connection with an evaporator chamber (4), through which breathing gas flows. The evaporator (5) is provided with a porous sintered glass or ceramic with a pore size of 10 .mu.m to 40 .mu.m in a first, lower, unheated area (14), and the evaporator (5) is provided with a porous sintered metal with a mean pore size of 50 .mu.m to 200 .mu.m in a second, upper area (15) heated by means of a heater (6).