For a compact unit, the Air-O-Swiss 7133 humidifier can handle very large rooms, up to 600 square feet. It operates by sending water by an ultrasonic vibrator that turns the water to a fine mist. The mist is driven from the unit by a fan. The unusual thing about this unit is that you have the choice of cool or warm mist humidification. Cool mist reduces operating costs and is generally preferred when you don't want to warm the room on a hot day. Warm mist facilitates the release of medication with the vapor. Running in the warm mist mode allows longer intervals between cleaning as well.

Dual vapor output knobs allow you to adjust the amount of humidity in the room. One is for warm mist and the other for cool. As there is no humidity readout, you cannot dial up a specific humidity level. So getting the right level requires a bit of trial and error. Inexpensive, battery-operated thermometer/hygrometers are available should you want to maintain a finer control of room humidity.

Bacteria are eliminated from water before vaporization as it flows by an ionic silver stick, a proven method for sterilizing water. The ionic silver stick should be replaced every year, and the demineralization cartridge should be replaced every three months. Minerals are prevented from being vaporized by an effective demineralization cartridge, so white dust on furniture and mineral build-up in the tank are minimized.

Warranty
3 years