What is the difference between a Direct Vent and a B-Vent gas hearth product?

A B-vent must be vented vertically and uses fresh air from inside the home to provide oxygen to the fire. A direct vent has a sealed glass front and pulls all of its fresh air from outside the home. Direct vents can be vented vertically or horizontally through an exterior wall. Direct vents are a completely sealed system; B-vent appliances are not.