A humidifier is a household appliance used to increase indoor humidity which can help improve dry environments and provide a more comfortable living or working environment. Ultrasonic humidifiers increase moisture in the air by generating water mist through high-frequency vibration; steam humidifiers generate steam by heating water; and evaporative humidifiers increase humidity by evaporating water. Humidifiers have different tank capacities so you can choose the right capacity to meet the needs of different sized spaces.