An appliance vent must terminate at least how far away from any building mechanical air inlet?

In gas appliance venting regulations, it's crucial to ensure that the exhaust gases do not re-enter the building through fresh air inlets or windows. The requirement for vent termination distance from any mechanical air inlet is primarily to prevent contamination of the incoming air, which could lead to unsafe conditions or impaired appliance function.

The correct answer, which states that an appliance vent must terminate at least 6 feet away from any building mechanical air inlet, aligns with established safety codes. This distance is intended to create a buffer zone that allows for proper dispersion of exhaust gases, minimizing the risk of them being drawn back into the building's ventilation system. This helps maintain indoor air quality and the safe operation of gas appliances.

The other distances provided in the alternative answers either do not offer sufficient separation or are not standardized as per most safety regulations. Therefore, adhering to the 6-foot guideline is an important aspect of ensuring safe installation and operation of gas appliances in relation to building ventilation systems.