Which of the following statements best describes a heating boiler's capacity?

• A. It is based on the fuel type used
• B. It is expressed in square feet of radiation
• C. It varies with the ambient temperature
• D. It is a measurement of water volume

Answer: (B)

The capacity of a heating boiler is most appropriately expressed in square feet of radiation. This measurement reflects the boiler's ability to provide adequate heat to a space by considering the surface area that contributes to heat transfer. When it comes to heating systems, understanding capacity in terms of square footage of radiation helps in determining how effectively a boiler can heat a given area based on the thermal characteristics of the space it serves.

While fuel type, ambient temperature, and water volume can influence a heating system's performance and efficiency, they do not directly define its capacity. Fuel type may affect the efficiency and operational costs, ambient temperature can influence the heating load, and water volume might relate to the boiler's overall water content, but these factors do not represent the actual capacity in terms of heating output. The square feet of radiation provides a standardized way to relate the boiler's output capabilities to the heating demands of a structure, making it the most relevant choice in this context.