Cool mist humidifiers are the most common humidifiers on the market. There are two types of cool mist humidifiers: ultrasonic models (best for single rooms and apartments) and evaporative models (best for multiple rooms and whole house humidification). Ultrasonic cool mist humidifiers use vibration to break water into ultra-fine droplets, which produces a visible mist. Cool mist evaporative models use a wick to evaporate water and humidify without a visible mist.