ALL exhausts must go outside for ANY type of combustion stoves. (coal, pellet, etc..)
A direct vent and/or power vent, is basically that, it is a blower that pushes or sucks the exhaust gases outside, YOU still must have it vented outside, but does not require a tall chimney, just a opening on the outside with either the power vent or a Tee and Cap.
Direct vents mount on the stove and PUSH the air outside.
A power vent, mount on the side of the building and pulls the exhaust gases outside.
ie. Pwer Vent
Do a search on here for Power Vents....