What does boiler horsepower define?

Boiler horsepower is specifically defined as the ability to evaporate a certain amount of water per hour at a specified temperature. The correct choice highlights that boiler horsepower can generate the evaporation of 34.5 pounds of water per hour at a supply temperature of 212 °F, which is a standard measurement in the industry. This definition points to the efficiency and capability of the boiler in producing steam, showing its performance in terms of heat transfer and energy usage.

Understanding this definition is crucial for professionals working with boilers, as it allows them to evaluate the capacity and output of a boiler system effectively. This measurement also plays a significant role in determining how a boiler fits into the larger system of steam and hot water generation in various applications.

The other options, while related to boiler performance, do not accurately describe the specific standard definition of boiler horsepower. The rate of steam generation and heat output pertain to broader aspects of boiler operation, and the size of the boiler in gallons pertains to its physical dimensions rather than operational capacity. Therefore, the accurate definition provided by choice B is essential for clarity and operational standards in the field.