Moisture from the dryer that is not vented can cause walls to become wet. Moisture behind walls or in any area of the house can cause mold to develop, making the home unsafe to live.
Lint will blow throughout the house if the dryer is not vented outdoors. Even if the dryer is kept in a basement, lint can make its way throughout the house through the air ducts and walls. Respiratory problems and allergies can be caused by lint dust.
Dryers that are vented with an indoor dryer vent assembly that allows heat from the dryer into the room can cause moisture to escape into the home. These types of assemblies are not safe for dryer venting and should not be considered for this use.