Can a 2 inch diameter round duct be utilized as combustion supply air for an appliance?

A 2-inch diameter round duct can be utilized as combustion supply air for an appliance because it meets the basic requirements defined in the relevant codes and standards for air supply. For most residential applications, specifically for smaller appliances like furnaces and water heaters, this duct size is deemed sufficient for providing the necessary combustion air.

When determining if a duct is adequate for combustion air supply, the key factors to consider include the appliance's BTU input and the design requirements for ventilation. In many cases, a duct of this size can handle the air flow required for appliances with lower BTU ratings, often those below a certain threshold, making it acceptable for direct use without additional modifications or larger ductwork.

Furthermore, each option presented considers specific scenarios, but as per standard practices, utilizing a properly installed 2-inch duct for combustion air under typical conditions aligns with industry standards. Thus, the assertion that it can be used safely and effectively holds true under standard application guidelines.