Cast iron boiler capacity:

When considering the capacity of cast iron boilers, the ability to increase capacity by adding sections is a key factor. Cast iron boilers are constructed in a modular manner, which allows for the addition of extra sections to increase the overall heating capacity. This modular nature means that as demand for heat increases, more sections can be added to accommodate that demand without having to replace the entire boiler system.

In practice, adding sections helps maintain efficiency and functionality, as each section can contribute to the heating output of the boiler. However, it's important to ensure that the design and installation comply with relevant codes and specifications to ensure proper operation and safety.

While it might seem like increasing section size could enhance capacity, it fundamentally doesn't work in the same way as adding additional sections; once a boiler is assembled, modifying its original size can create complications or inefficiency. This distinguishes the correct answer, as the act of simply adding sections directly contributes to the boiler's operational capacity in a straightforward manner.