Everything There is to Know About the Fire Tube Boiler

A fire tube boiler is a type of boiler that is designed to transfer hot gases from the heat source that will pass through a series of tubes, which then ran thought cycled through a sealed drum that contains water. The process transfers the heat through the water, which then will generate steam. Using a fire tube boiler provides far greater heating surface area than flue boiler systems. A fire tube steam boiler was originally primarily used by steam locomotives but continues to be used due to its practicality, simplistic and easy to operate design, which is also fairly inexpensive to purchase. Fire tube boilers have the ability to generate low degrees of pressure, are exceptionally versatile, and have a variety of different designs and variations.

Scotch Marine Boiler

The Scotch marine boiler is dramatically different from its predecessors; it uses a large number of small tubes, which gives a far greater heating surface area for its weight. With the Scotch marine boiler, the furnace is a large diameter tube, which is located inside of the boiler. Many of the previous scotch boilers contain two or three different boilers

Locomotive Boiler

A locomotive boiler, which is also referred to as a firebox boiler is a multi-pass boiler that is typically found in colleges, universities, or in an area where the system is used to produce steam or to create hot water. A one-pass boiler design allows combustion products to pass through the locomotive boiler, which depending on the arrangement may contain tubes, baffles. Some designs may contain a three-pass or two-pass.

Horizontal Return Tubular Boiler

The horizontal return tubular boiler is one of the oldest and simplest industrial boilers, which is why it’s still being produced to this day. The boiler features a shell, horizontal tube flues on each end of the shell and tubes which are connected to the tube flues. The boiler is often mounted above the steel furnace or within a brickwork setting. Here’s how it works, once the combustion products leave the furnace, they will then make their way through the tubes located on each end of the boiler, leaving out the other end of the boiler, which is then directed through the chimney or stack.

Immersion Fired Boiler

An immersion fired boiler is a single pass fire tube boiler that was developed In the 1940s by Sellers Engineering. It only uses firetubes and functions as a furnace and combustion chamber, which has multiple burner nozzles that inject gas and premixed air. The immersion fired boiler reduces the stresses caused by thermal heat, which due to its construction lacks refractory brickwork.


There are different variations of fire tube boilers, including the water tube and reverse flame. Locomotive and immersion fire boilers will often have a water tube to help increase the heating surface. A vast majority of modern shell boilers will use a reverse flame design; the burner will fire into a blind furnace, which then causes the combustion gasses to double back.