Most ventless dryers either use condensation or a heat pump to remove moisture from the dryer. Ventless dryers do not require exhaust hoses but do need to drain water.
Airflow is important in traditional dryers both to apply heat to the clothing and to remove moisture from the air. As clothes dry, the liquid water converts to water vapor; if this water vapor is not removed, it condenses on the clothing again. Traditional dryers simply blow this water vapor out of the system, while ventless systems use other techniques to remove it. Since ventless dryers do not release heat outside, the heat generated warms the home, leading to reduced heating costs in cold areas but higher air conditioning costs is warm areas.
In condensation units, the air in the dryer is moved into a region where it is cooled. As the air cools, its water vapor is converted into liquid form, where it is then drained from the system. Once water vapor has been removed from the air, it is heated again. Heat pump dryers pull ambient air from the room and create a cold zone within the dryer capable of creating condensation within the unit, which is then drained. Heat pumps use electricity but operate more efficiently than both traditional and condensation units.