A steam humidifier provided by the present invention has a tank having a reservoir section and a cover removably and sealingly secured thereto. The tank contains water during a humidifying operation in which the humidifier humidifies an indoor environment. The cover has a heating element mounted thereon and extending therefrom into the reservoir section and a steam outlet assembly mounted thereon and extending therethrough into the tank. The heating element evaporates at least a portion of the water during the humidifying operation into steam output through the steam outlet assembly to humidify the indoor environment.