These humidifiers are preferred for large homes and for low heat sources such as hydronic fan coils and heat pumps. A steam humidifier senses the humidity in the home using a humidistat. Water in a reservoir is converted to steam. The humidifier works in tandem with your central air system. The blower will turn when the humidistat requests additional moisture to be introduced. Steam humidifiers do not require heat from any additional source to evaporate the water into the air. They can produce enough moisture for very large homes. The humidistat will maintain very accurate moisture levels for the entire home.