Your Holmes Ultrasonic Humidifier helps bring relief from sinus irritation and other effects of dry air. You will surely enjoy the filter-free operation, variable mist control, auto shut-off and anti-microbial protection. Anti-microbial protection is infused into the plastics to help prevent the growth of bacteria that can cause stains and odors or adversely affect performance. Filter-Free Operation, 1.3 Gallion tank capacity, Tank will operate throughout the night on one filling, Space-saving attractive tower design, 24-hour run time.