Classify a gas fireplace venting system correctly as direct-vent, B-vent, or vent-free before installation or service

Steps

1. Identify the appliance's listing/rating plate to determine its combustion-air and venting classification rather than assuming from appearance alone
2. Confirm direct-vent appliances draw outside combustion air through a sealed system and vent flue gas outside through a coaxial or two-pipe system per the specific appliance's listed venting instructions
3. Confirm B-vent (natural-draft, Category I) appliances draw combustion air from indoors and vent through a listed double-wall metal vent per the appliance manufacturer's instructions and the National Fuel Gas Code (NFPA 54/ANSI Z223.1)
4. Confirm vent-free (unvented) appliances have no chimney/vent connection at all and are subject to separate listing, room-size, and oxygen-depletion-sensor requirements that differ materially from vented appliances
5. Never mix venting components or lengths/terminations across appliance types or manufacturers — use only the vent system components listed with that specific appliance
6. Verify local/state adoption status for vent-free appliances before installing, since some jurisdictions restrict or prohibit unvented gas appliances