Gas Fitter Practice Test 2026 – The All-in-One Guide to Mastering Your Certification!

A 2-inch diameter round duct can indeed serve as combustion supply air for an appliance, as long as it is installed properly and meets all relevant codes and standards. The primary function of combustion air is to provide sufficient oxygen for the fuel-burning appliances to operate efficiently and safely.

For a duct of this size, it is important to ensure that the appliance being served does not exceed the air supply requirements specified by the manufacturer’s installation instructions and any applicable building codes. Generally, a properly sized duct can accommodate the necessary airflow requirements for many smaller appliances, facilitating safe combustion.

In contrast, the other options present specific conditions that are not universally applicable or necessary. For instance, mentioning a specific BTU input threshold or a minimum ventilation air size relates to larger appliances that may require more substantial airflow due to their increased energy use. However, these conditions are not a blanket requirement for all applicable scenarios. Therefore, a 2-inch round duct can suffice for certain appliances without being contingent upon those additional specifications.