What is the minimum area for vertical ducts delivering outside combustion air to a 45,000 BTU/h rated water heater?

To determine the minimum area for vertical ducts delivering outside combustion air to a 45,000 BTU/h rated water heater, it's essential to consider the guidelines outlined in the National Fuel Gas Code (NFPA 54) and the specific requirements for water heater installations.

In this case, the correct answer indicates that the minimum area required is a 12-inch square duct. This value is derived from the need to ensure adequate airflow for combustion, which is critical for the efficient and safe operation of the water heater.

When calculating the necessary duct size for outside combustion air, the general rule is that the area required varies with the input BTU rating of the appliance. For every 1000 BTUs, a certain amount of air is required, typically around 1 square inch of free area for each 1000 BTUs. Hence, for a water heater rated at 45,000 BTU/h, this translates to needing a total of around 45 square inches of free area for proper combustion air.

The 12-inch square measurement provides 144 square inches of area, which significantly exceeds the requirement. This ensures that there is ample airflow, which fosters optimal combustion and prevents issues related to inadequate oxygen supply, such as incomplete combustion or the production