What is a key characteristic of a firetube boiler?

A firetube boiler is characterized primarily by the design where flames and hot gases pass through the tubes that are surrounded by water. This design allows heat from the combustion process to transfer effectively to the water, converting it to steam.

This characteristic is critical because it highlights the heat transfer mechanism that distinguishes firetube boilers from other boiler types, such as watertube boilers, where water flows through tubes surrounded by the flame and combustion gases. In a firetube design, the hot gases directly contact the outside of the tubes, providing efficient heating.

The other options do not accurately describe the defining features of firetube boilers. For instance, while some boiler systems can be automated, firetube boilers do not inherently possess automation as a defining characteristic; this can apply to various types of boilers. Additionally, having a large water storage capacity is more typical of certain boiler designs but not a distinctive trait of firetube boilers. Finally, the flow of water through tubes is an illustration of watertube design rather than firetube. Thus, understanding that the hallmark feature of firetube boilers is the passage of flames and hot gases through the tubes is essential for grasping their operational principles.