What is the term for a gas appliance that draws combustion air from the outside?

The term for a gas appliance that draws combustion air from the outside is "direct vent appliance." This type of appliance is designed to use outside air for combustion, eliminating the need for indoor air, which can enhance energy efficiency and safety. By pulling fresh air from the exterior, direct vent appliances can operate in tightly sealed buildings without depleting indoor oxygen levels, thus preventing potential asphyxiation risks associated with other types of gas appliances.

Conversely, conventional appliances typically rely on indoor air, which can lead to issues in poorly ventilated spaces. Indoor vent appliances still require a separate venting system, while non-vented appliances do not pass exhaust gases outside, posing safety hazards related to incomplete combustion and indoor air quality. Therefore, direct vent appliances are specifically engineered for optimal operation while ensuring safety by sourcing combustion air directly from the outside environment.