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Which Boiler is the Best Fit for Your Facility – Firetube or Watertube?

Tip Sheet: March 2013

Key Facts

  • A firetube boiler costs 25 to 40 percent less than a comparatively sized watertube boiler
  • Firetube boilers are more efficient and easier to clean than watertube boilers
  • A watertube boiler is best for a facility that needs its boiler to operate at a high capacity or at a high steam quality

The decison to purchase a firetube versus a watertube boiler depends on both the application and steam requirements.


When purchasing a boiler, deciding whether to buy a firetube or watertube one typically is the first step. The names of these two types of boilers reflect their respective operational design. In a watertube boiler, water flows through the tubes, which surround the furnace and convection area(s) fired by the burner. In a firetube boiler, the fire or hot flue gases from the burner travel through the furnace and tubes surrounded by the water inside the shell.   


The answer of whether to purchase a firetube or a watertube boiler depends on both the application and steam requirements, as well as other factors.   


Advantages of a Firetube Boiler   

A firetube boiler costs 25 to 40 percent less than a comparatively sized watertube boiler. The price difference is primarily due to manufacturing costs. Constructing a watertube boiler requires more expensive materials and is more labor-intensive than constructing a firetube boiler.  


Firetube boilers are also more efficient. In order for a watertube boiler to equal the efficiency of a firetube boiler, a combustion air preheater or feedwater economizer has to be added, which increases the overall cost of the unit.  


In addition, the design of a firetube boiler makes it easier to clean. Inspecting and cleaning tubes in a watertube boiler is more difficult, so the quality of the feedwater is extremely important. A firetube boiler is a bit more forgiving with regard to feedwater quality. However, both require constant feedwater monitoring and a sound chemical treatment program to maintain boiler integrity.  


In terms of space, the firetube boiler also requires less headroom.  


Advantages of a Watertube Boiler   

If a facility needs its boiler to operate at a high capacity, the watertube packaged boiler is best. Firetube boilers are limited to approximately 2,500 HP, or about 86,000 lb/hr. Watertube boiler packages are designed to handle larger capacities, up to approximately 650,000 lb/hr, which is equivalent to about 19,000 HP.  


A watertube boiler also is superior when a facility’s needs dictate high temperature and steam pressure. A firetube boiler is limited to approximately 350 psi for steam; however, a watertube can reach 900 psi, and specially designed watertube boilers can operate at pressures up to 1,500 psi. For large-capacity loads, large design pressure requirements, tracking rapid load swings or extreme horsepower needs, the watertube boiler essentially is the only choice.  


A watertube boiler also has higher steam quality (amount of moisture in the steam itself) compared to a firetube boiler. If steam quality is critical to the operation, the watertube boiler is superior. In addition, a superheater can be integrated into a watertube boiler, but not into a firetube one.  


There is not as much pressure drop through a watertube boiler size-for-size compared to a firetube boiler, and as such, its fan motor HP is less. In the traditional four-pass firetube boiler, there are four passes of resistance, and pressure drop incrementally increases at each pass.  


Watertube boilers also have a space advantage when compared to firetube boilers of equal capacity. This is due to the length of the firetube and the need to allow room in front or back for tube pulling and respective door swings. The watertube only requires a few feet around the boiler for maintenance.  


Watertube boilers normally are applied to process steam or high temperature, hot water applications having large capacities, meeting or exceeding the limits of firetube boilers. Both types are used in process applications. The firetube can be used for low-pressure steam heating or process and hot water heating applications. The large watertube boiler is not designed for low-pressure (15#) operation.  

Determining whether your facility would derive more benefit from a firetube or watertube boiler is the first essential step. There are a number of models available in each boiler design, so consult an authorized boiler representative to determine the one that best meets your facility’s needs.