Firetube or Watertube? What's the difference?

Boilers come in many different sizes, shapes and designs. This creates quite a challenge for those of us that do not purchase boilers on a regular basis. The choice between a firetube design and a water tube design can become very confusing for novice boiler buyers.


We thought a quick discussion on the advantages and disadvantages of these boiler designs might prove helpful.



firetube boilers


The Hurst LPE "Performance" boiler is America's most heavily designed and built boiler in its class. 

A welded steel firetube boiler, the LPE has extra heavy 12 gauge tubes for extended life. All tubes are attached to the tube sheets by rolling and flaring. There are no welded tubes in the LPE.

Thickest materials used in the industry...

  • Boiler shell is 5/16" thick boiler plate.
  • Twin boiler tube sheets are 1/2" thick boiler plate.
  • Insulation is 2" mineral wool and is lagged with 22 gauge boiler jacket.
  • Extra heavy 3" channel iron boiler skids.

Designed to last with special industrial grade features...

  • Couplings are 3,000 psi.
  • Flanged, detachable front and rear smoke boxes.

So What is a Firetube Boiler?

The name firetube is very descriptive. The fire, or hot flue gases from the burner, is channeled through tubes that are surrounded by the fluid to be heated. The body of the boiler is the pressure vessel and contains the fluid. In most cases this fluid is water that will be circulated for heating purposes or converted to steam for process use. 

Every set of tubes that the flue gas travels through, before it makes a turn, is considered a "pass". So a three-pass boiler will have three sets of tubes with the stack outlet located on the rear of the boiler. A 4-pass will have four sets and the stack outlet at the front.

Firetube Boilers are:

  • Relatively inexpensive
  • Easy to clean 
  • Compact in size
  • Available in sizes from 600,000 btu/hr to 50,000,000 btu/hr
  • Easy to replace tubes
  • Well suited for space heating and industrial process applications

Disadvantages of Firetube Boilers include:

  • Not suitable for high pressure applications 250 psig and above
  • Limitation for high capacity steam generation


watertube boilers

Unilux Series "Z" Water Boilers:

Provide 85% efficiency to your customers! The unilux series "Z" boilers are available from 20 BHP to 1500 BHP as cataloged standard with larger sizes available by request. This unique, modern forced draft design is the ultimate in water boiler technology. Available as factory packaged or field erect (FE). 20 year warranty on vessel as standard.

What is a Watertube?

A Watertube design is the exact opposite of a fire tube. Here the water flows through the tubes and are incased in a furnace in which the burner fires into. These tubes are connected to a steam drum and a mud drum. The water is heated and steam is produced in the upper drum. Large steam users are better suited for the Water tube design. The industrial watertube boiler typically produces steam or hot water primarily for industrial process applications, and is used less frequently for heating applications.

Watertube Boilers are:

  • Available in sizes that are far greater than the firetube design. Up to several million pounds per hour of steam.
  • Able to handle higher pressures up to 5,000 psig
  • Recover faster than their firetube cousin
  • Have the ability to reach very high temperatures

Disadvantages of the Watertube design include:

  • High initial capital cost
  • Cleaning is more difficult due to the design
  • No commonality between tubes
  • Physical size may be an issue

The best gauge of which design to consider can be found in the duty in which the boiler is to perform. Fortunately most boiler sales agencies offer a number of boiler designs and can help you make the correct choice. Ask these professionals what they would recommend and have them explain why.

Our Boiler Parts Department

Don't forget to stop by and visit our boiler parts department. We are the experts when it comes to finding those "hard to find" parts. 

P.C. McKenzie Company
P.O. Box 112638
Pittsburgh, PA 15241
Fax: 412-257-8890
Phone: 412-257-8866
P.C. McKenzie Company
1365 McLaughlin Run Road
Pittsburgh, PA 15241

Firetube Boiler  or Watertube Boiler?