The burner box of a firetube boiler could be:

The burner box of a firetube boiler can be either inside or outside the boiler, depending on the specific design and configuration of the boiler system. This versatility allows for varied installations and can influence the efficiency and safety of the operation.

When the burner box is located inside the boiler, it can contribute to better heat transfer and efficiency, as the immediate environment is more conducive to maintaining higher temperatures and optimizing combustion. Conversely, placing the burner box outside can facilitate easier maintenance, improve accessibility, or allow for the use of pre-mixed fuel-air mixtures that enhance combustion stability.

Therefore, the correct answer recognizes the flexibility of design in firetube boilers, ensuring that both internal and external burner box configurations are valid options in the context of boiler operations.