How is boiler horsepower defined in terms of evaporation?

Boiler horsepower is a measure of a boiler's capacity to produce steam, and it is specifically defined as the ability to evaporate 34.5 pounds of water into steam per hour at a temperature of 212 degrees Fahrenheit, which is the boiling point of water at standard atmospheric pressure. This definition brings clarity to the performance of a boiler in practical applications, allowing engineers and operators to assess how efficiently a boiler can convert water into steam.

Understanding this definition helps in comparing different boilers and their efficiencies in steam production. The numerical value (34.5 pounds) is derived from the amount of steam required to perform useful work in industrial processes, making it a standard measure in the field.

Other options relate to the heating surface area of boilers but do not define boiler horsepower in terms of evaporation. The mention of square feet in those choices does indicate some relevant characteristics of boilers; however, they do not directly answer what boiler horsepower is quantified by. Thus, defining boiler horsepower in terms of evaporation provides a direct and useful metric for evaluating boiler performance.