Which of the following best describes direct-vent appliances?

Direct-vent appliances are specifically designed to draw outdoor air for combustion and to vent combustion gases directly outdoors. This design is crucial for maintaining indoor air quality and safety, as it prevents the accumulation of harmful gases within the living space. These appliances are constructed with a sealed combustion system, which ensures that air used for combustion is taken from outside the building rather than depleting indoor air supplies.

This feature not only enhances the efficiency of the appliance but also reduces the risk of backdrafting, where combustion gases might otherwise be drawn back into the living area. By utilizing outdoor air, direct-vent appliances can operate effectively in tightly sealed buildings without compromising fresh air availability for other household needs or appliances.

In contrast, appliances that expel combustion gases into the building or use indoor air for combustion can lead to hazardous situations and may not be compliant with safety regulations, while those requiring a separate ventilation system may not offer the streamlined operational benefits that direct-vent systems provide.