The two most popular boiler types that you can choose for your specific application are a water tube or a fire tube boiler. It is not always easy to choose the type that is best for your application. There are some significant differences to consider for each type.  fire tube boiler

Fire tube boilers usually have a lower operating cost comparable to similarly sized water tube boilers. Water tube boilers are considered safer by design and generally can operate many years longer than fire tube boilers.

A fire tube boiler is a type of boiler in which hot gases from a fire pass through one or more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam.

Their advantage over boilers with a single large flue is that the many small tubes offer far greater heating surface area for the same overall boiler volume. The general construction is as a tank of water penetrated by tubes that carry the hot flue gases from the fire. The tank is usually cylindrical as it is the strongest practical shape for a pressurized container. This cylindrical tank may be either horizontal or vertical.

Fire tube boilers are generally smaller in design. They have a larger water volume than similar size water-tube boilers, causing them to take longer to bring up to operating temperature from a cold start. Fire tube boilers are not suitable for pressures above 350 psig.

Because the fire-flume boiler itself is the pressure vessel, it requires a number of safety features to prevent mechanical failure:

  • Safety valves release steam before a dangerous pressure can be built up
  • Fusible plugs over the firebox melt at a temperature lower than that of the firebox plates, thereby warning the operators by the noisy escape of steam if the water level is too low to cool the firebox crown safely.
  • Stays or ties, physically link the firebox and boiler casing, preventing them from warping. Since any corrosion is hidden, the stays may have longitudinal holes, called tell-tales, drilled in them which leak before they become unsafe.

There are various types of fire-tube boilers. A few types are:

  • Vertical fire tube boilers that have a vertical cylindrical shell, containing several vertical flue tubes.
  • Horizontal return tubular boilers that have  a horizontal cylindrical shell, containing several horizontal flue tubes, with the fire located directly below the boiler's shell, usually within a brickwork setting
  • Immersion fired boiler that has only fire-tubes, functioning as a furnace and combustion chamber also, with multiple burner nozzles injecting premixed air and natural gas under pressure. 

The Advantages of Fire-Tube Boilers:

  •  Compact in construction.
  •  Fluctuation of steam demand can be met easily.
  •  Cheaper than water-tube boiler.

Disadvantages of Fire-Tube Boilers:

  • The time required for steam pressure to rise can be quite long. 
  • Steam output pressure cannot be very high since the water and steam are kept in the same vessel.
  • Steam received from fire-tube boilers is not very dry.
  • The steam drum is always under pressure, so there may be a chance of an explosion. 

To operate safely, a rigorous schedule of maintenance is needed. Typically, this  will involve regular external inspections (including the inside of the firebox, washouts (with an internal inspection), periodic detailed examination and a general overhaul.

The tube plates, the fusible plug and the heads of the firebox stays should be checked for leaks on a daily basis. The correct operation of the boiler fittings, especially the water gauges and water feed mechanisms, should be confirmed each day.Steam pressure should be raised to the level at which the safety valves lift and compared with the indication of the pressure gauge also on a daily basis.

A very reliable and popular fire tube boiler choice is the  Burnham Series 3 Firetube Boiler. The Burnham Commercial Wetback Packaged Boiler can save you thousands of dollars over the life of your boiler. The quality engineering takes maximum advantage of long-term energy and maintenance efficiencies. Unless you take those efficiencies into consideration along with price when you choose a boiler, you can be in for enormous hidden costs. The Series 3 matches burner to boiler, providing a fuel efficient low-maintenance package. It takes maximum advantage of long-term energy and maintenance efficiencies.

If you need boiler maintenance, a new boiler or one repaired, Ohio Plumbing & Boiler is your trusted expert service company. We repair and install all makes and models of commercial and residential heating boilers.  Our company has been repairing and maintaining all types of boilers in the area for over two decades.


We service and install gas, electric, propane and oil boilers for commercial, industrial and residential customers. 

Topics: Fire-tube boilers