A fire-tube is a type of boiler that uses hot gases from a combustion source to heat water. In this design, the hot gases flow through tubes that are surrounded by water. As the gases pass through, they transfer heat to the water, producing steam or hot water for various applications, such as heating or power generation. Fire-tube boilers are commonly used in industrial settings and are known for their simplicity and efficiency. They are typically easier to maintain than other boiler types, such as water-tube boilers, making them a popular choice for many facilities.