Windy City Reps

Understanding Firetube vs. Watertube Boilers

February 14, 2022

There are many different designs of boilers, as they have been used in commercial settings for more than two centuries. However, for many HVAC systems, a critical distinction is firetube vs. watertube boilers. Each has their place; in fact, a project may require one of each type, or a series of boilers, to provide the hydronic or steam system with the proper heat supply. Below are some of the key considerations regarding the design, installation, and operation of each system.

Basics of Design

​As the names imply, the principal difference between watertube boilers and firetube boilers is whether the combustion gases surround the water, or vice versa. 

Watertube Boilers

​In a watertube design, rows of symmetrical water tubes are surrounded by hot gases as they transfer heat to the fluid contained therein.  This vessel configuration results in a reduced water volume as compared to firetube boilers. The reduced water volume correlates to additional system pumping considerations; watertube boilers often require boiler circulating pumps and a primary-secondary pumping configuration. 

If you’re considering installing a watertube boiler for your heating needs, they offer several benefits. First, watertube boilers are both lighter and smaller than firetube boilers—a key concern if you’re working to retrofit an HVAC system and space is a concern. 


Image courtesy of Cleaver Brooks

​Firetube Boilers

​Firetube boilers are a bit more straightforward. First, the system runs the combustion gases through tube surrounded by water. This results in a higher volume of water in the boiler. Higher water provides additional thermal capacitance of the equipment, reducing vulnerability to varying flow rates through the boiler. The higher water volume and reduced vulnerability to varying flows allows for simpler pumping strategies.

Firetube boilers are usually used for heating commercial buildings of all sizes. Whether a small multifamily residential building or large educational campus, firetube boilers are available to meet the need.​

Firetube boilers are often physically larger and weigh more. This is an important consideration when dealing with retrofit opportunities as there may be structural ramifications of utilizing heavier equipment.  

​Installation and Maintenance

Watertube Boilers

Watertube boilers have a much higher initial unit and installation cost than their counterparts. Because repairs and maintenance must be performed internally, upkeep for watertube boilers also tends to be pricier. However, watertube boilers can heat smaller amounts of water efficiently, which increases their lifespan significantly compared to firetube boilers. 

Firetube Boilers

​Generally, commercial firetube boilers tend to be more expensive compared to watertube boilers to purchase. This is a result of the amount of material that goes into each vessel type. Cost of ownership typically is less with commercial firetube boilers given their reparability, and operating efficiency resulting from application flexibility means that costs are often similar when comparing the two boiler types.

Maintenance vs. Fuel Cost

A good maintenance program consisting of routine inspection and cleaning is essential to maintaining the efficiency of any boiler and can go a long way towards keeping fuel costs low. For example, a buildup of soot within the tubes no thicker than 1/32 of an inch can reduce the efficiency of the boiler by as much as 12 percent. 

As noted in the example above, that can result in over 15 percent additional fuel usage.Keep a daily log of the flue gas temperature of the boiler to spot potential problems early; an upward trend in stack temperature may indicate that the boiler is in need of cleaning or adjustment. Routine inspections and preventative maintenance will pay for themselves in keeping boiler efficiency up and fuel costs down. See the Boiler Efficiency Guide from Cleaver Brooks for more information.

​Making A Choice 

​Ultimately, both firetube and watertube boilers each offer their own benefits and drawbacks—your choice is likely to be informed by your building’s size, your heating needs, and your budget. We’d recommend consulting with an HVAC professional before making your decision, as no two projects are alike. 

Compare Our Partners’ Firetube vs. Watertube Boilers

Windy City Ventures represents leading manufacturers of hydronic heating units, and we understand how important it is to take multiple considerations like budget and existing systems into account when specifying for firetube vs. watertube boilers. To learn more about our advanced technology and discuss how we can meet and exceed your needs, call us today at 630-590-6933.

At Windy City Representatives, we partner with premier HVAC equipment providers to help you design the best HVAC system for your building or facility’s needs and budget. 

Contact us today for a quote or bid.
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Oak Brook, IL 60523
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