The recommended humidity level for a house normally ranges from 35 to 45 percent. At this humidity level, it is neither too dry nor too moist, which allows the residents to live comfortably. It also provides the best condition to keep the rooms and furniture from damage.
When there is excessive moisture in the air during winter, a house may use a heating system such as a furnace. Sometimes, a dehumidifier is additionally used also to maintain proper humidity level. In contrast, the air sometimes becomes too dry as a result of using a heating system. In this case, using a portable or centralized humidifier may be necessary to restore indoor moisture to the correct level.