An appliance constructed and installed so that all air for combustion is derived from outdoors and all gas flue gases are discharged to the outdoors is a what?

An appliance constructed and installed so that all air for combustion is derived from outdoors and all gas flue gases are discharged to the outdoors is a what?

• A. Natural vent appliance
• B. Direct-vent appliance
• C. High efficiency furnace
• D. Category III appliance

Answer: (B)

Direct-vent appliances are designed to take all combustion air from outdoors and to vent all combustion products directly to the outdoors. This sealed combustion approach keeps indoor air from being used for burning and prevents any combustion gases from spilling back into the living space. It commonly uses a coaxial or two-pipe venting system through an exterior wall or roof. This matches the description exactly: air for combustion is drawn from outside and the flue gases are discharged outside, rather than relying on indoor air or natural draft. A natural-vent appliance would pull combustion air from the room and vent through a chimney or vent stack; a high‑efficiency furnace describes efficiency, not the air source/venting path; a Category III appliance refers to a venting category related to mechanized venting, not specifically the outdoor air/indoor air separation described here.

Direct-vent appliances are designed to take all combustion air from outdoors and to vent all combustion products directly to the outdoors. This sealed combustion approach keeps indoor air from being used for burning and prevents any combustion gases from spilling back into the living space. It commonly uses a coaxial or two-pipe venting system through an exterior wall or roof.

This matches the description exactly: air for combustion is drawn from outside and the flue gases are discharged outside, rather than relying on indoor air or natural draft. A natural-vent appliance would pull combustion air from the room and vent through a chimney or vent stack; a high‑efficiency furnace describes efficiency, not the air source/venting path; a Category III appliance refers to a venting category related to mechanized venting, not specifically the outdoor air/indoor air separation described here.