Two means of feedwater makeup are required if the boiler’s heating surface exceeds how many square feet?

• A. 500 ft²
• B. 1000 ft²
• C. 250 ft²
• D. 750 ft²

Answer: (A)

When a boiler has more heating surface, it can generate more steam and evaporate water more quickly. That higher demand means makeup water must be available reliably, even if part of the system isn’t working. To ensure continued water makeup and prevent low-water conditions, larger boilers use two independent means of supplying makeup water. The threshold used here is 500 square feet of heating surface: if the boiler exceeds that size, two separate makeup sources are required so a single failure won’t trip the operating boiler. The other numbers correspond to different boiler sizes and aren’t the cut-off in this rule, which is why 500 ft² is the appropriate standard.