Gas Appliance Venting Options Hearth products are vented in three ways: natural draft (vented through the roof), direct-vent, and vent-free. Below are the options for gas hearth appliances.             Natural Draft (Class B) Venting Natural draft hearth appliances take in combustion air from inside the home and vent products of combustion outside the home.       Direct Vent Direct-vent appliances draw combustion air from the outdoors and exhaust its combustion products to the outdoors, eliminating the need for a standard chimney system. A glass panel in direct-vent units is critical to keeping the combustion system sealed from the home, maintaining high efficiency and indoor air quality. Direct-vent piping can go out the wall directly in back of the unit or terminate vertically above the roof. Various models differ. Check with your retailer. Currently, the majority of gas fireplace sales are direct vent units.                 Unvented or Vent-Free Unvented and vent-free refers to the kind of hearth appliance that draws its combustion air from inside