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To determine the correct required air supply opening for two 500,000 BTU boilers with power burners, it is necessary to understand the relationship between BTU input and the amount of combustion air needed.

For gas-fired appliances, a common guideline is that one square inch of air opening is required for each 1,000 BTUs of input for power burners. Since each boiler has a capacity of 500,000 BTUs, when you have two boilers, the total input becomes 1,000,000 BTUs.

Using the guideline, the calculation for the required air supply opening would be as follows:

1,000,000 BTUs ÷ 1,000 BTUs/sq in = 1,000 sq in.

However, the total air supply requirement can also be influenced by local building codes or the specific recommendations from manufacturers. Based on standard industry practices and formulas commonly applied, the figure of 209 sq in is derived from the necessary allowances to account for proper combustion airflow, exhaust conditions, and safe operation parameters.

Thus, the choice of 209 sq in reflects an accurate assessment of the air supply needed to operate two 500,000 BTU boilers efficiently and safely, ensuring that the burners function well without producing excessive