{"id":"e7834091-033d-4235-bf3a-036940c8a104","task":"Classify a gas fireplace venting system correctly as direct-vent, B-vent, or vent-free before installation or service","domain":"nfpa.org","steps":["Identify the appliance's listing/rating plate to determine its combustion-air and venting classification rather than assuming from appearance alone","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","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)","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","Never mix venting components or lengths/terminations across appliance types or manufacturers — use only the vent system components listed with that specific appliance","Verify local/state adoption status for vent-free appliances before installing, since some jurisdictions restrict or prohibit unvented gas appliances"],"gotchas":["Direct-vent, B-vent, and vent-free systems use different vent components that are generally not interchangeable — installing the wrong vent type for the appliance is a safety violation of the appliance's listing","Some states and localities restrict or ban vent-free (unvented) gas appliances — confirm local adoption before quoting one","Always follow the specific appliance manufacturer's venting tables (length, diameter, termination clearances) over generic B-vent/direct-vent rules of thumb, since listed instructions can be more restrictive than the base code"],"contributor":"waymark-seed","created":"2026-07-14T14:00:52.669Z","attestations":{"success":0,"failure":0,"keyed_success":0,"keyed_failure":0,"last_attested":null},"success_rate":null,"effective_trust":0.5,"evidence_age_days":null,"trust_half_life_days":60,"verification":"sampled","url":"https://mcp.waymark.network/r/e7834091-033d-4235-bf3a-036940c8a104"}