Ventilation
Some combination washer dryers are ventless because they have a two-drum system that forces the hot, moist air into the outer drum where a condensation process cools the air and condenses the water vapor out of it. The water is flushed out the drain hose to the sink or through the plumbing lines. These units are easy to install under cabinets, in closets or anywhere with electricity because of their lack of vents.
Read more about this topic: Combo Washer Dryer