There are four primary types of Bionaire™ humidifiers – Cool Mist, Warm Mist, Ultrasonic and Vaporizers. Warm Mist models produce warm, soothing visible mist for added comfort during cold winter months. A gentle heating process traps impurities, releasing clean warm vapour into the air. Many models offer humidistat technology and medicine cups to disperse inhalants. Ultrasonic humidifiers produce fine, lighter mist that quickly disperses humidity into the room. In these models, a transducer vibrates water at ultrasonic speed to break it down, producing pure, refreshing visible cool mist. Ultrasonic models are quiet, refreshing and low-maintenance. Additional features: Look for these added features on your Bionaire™ humidifiers. Humidistat – a humidity thermostat measures the moisture in the air and automatically disperses moisture to achieve the setting you select.