Boiler Blog | Nationwide Boiler Inc.

Selecting the right boiler for your facility is more than just a design choice – it directly impacts efficiency, reliability, operating costs, and emissions compliance. Among the most common designs are firetube boilers and watertube boilers, each with unique advantages depending on the application. These boilers can also be classified by pressure (low or high), output (steam or hot water), and steam temperature (saturated or superheated), adding further considerations to the decision-making process.

The following overview outlines the key differences between firetube and watertube boilers to help facility managers, engineers, and plant operators choose the system that best fits their needs.

What is a Firetube Boiler?

A firetube boiler, also known as Scotch Marine boiler, is one of the most traditional and widely used boiler designs. In this system, a large pressure vessel holds water, and tubes carrying hot combustion gases run through the vessel. As the gases pass through these tubes, heat is transferred to the surrounding water, gradually increasing its temperature until it produces either hot water or steam depending on the application. Because the “fire” or combustion gases are inside the tubes, the design is known as a firetube boiler.

Key Advantages:

• Lower upfront cost and simpler design
• Easier to operate and maintain
• Suitable for small to medium-sized facilities

Limitations:

• Slower to respond to load swings due to large water volume
• Design pressure capability is more compared to watertube designs

Firetube boilers are commonly utilized in industries and facilities such as small food processing plants, hospitals, schools, universities, and other heating applications where dependable steam or hot water is needed for steam systems operating at 150 psig and less.

What is a Watertube Boiler?

A watertube boiler operates differently than a firetube boiler. Instead of hot gases flowing through tubes surrounded by water, a watertube design allows water to circulate inside the tubes while the combustion gases pass around them. This configuration enables the system to handle much higher pressures and produce greater steam capacities than firetube units.

Key Advantages:

• Handles higher range of pressures, commonly up to 750 psig but pressures over 1000 psig are possible.
• Faster startup and load response
• More compact water content, reducing risk of catastrophic failure

Watertube boilers are commonly used in high-demand industries such as power plants, petrochemical plants, refineries, pulp and paper mills, large food processing, and large-scale manufacturing facilities, where high-pressure steam and higher capacities are required.

Limitations:

• Higher initial cost due to design and manufacturing differences
• Space requirements
• Typically, higher operation and maintenance costs

High Pressure vs. Low Pressure Boilers

Boilers are also defined by their maximum allowable working pressure (MAWP):

• Low Pressure Boilers: Operate at 15 psig or below. Commonly used for heating systems and hot water supply, they require less maintenance and are easier to manage.
• High Pressure Boilers: Designed for pressures above 15 psig. These units are essential for industrial steam production, power plants, and manufacturing processes where higher output is required.

Firetube boilers can be built for both pressure ranges, but watertube boilers are almost always high pressure due to their design.

Hot Water Boilers vs. Steam Boilers

While often confused, hot water boilers and steam boilers are separate classifications that can be applied to either firetube or watertube designs.

• Hot Water Boilers: Operate like large fuel-fired water heaters, producing hot water in the range of 120 - 220°F. These are primarily used for building heat, hydronic heating systems, and domestic hot water.
• Steam Boilers: Heat water beyond the boiling point to create steam. These systems are more powerful and used in industrial processing, sterilization, district energy systems, and power generation. Steam boilers may generate either saturated steam or superheated steam, depending on the application.

Saturated vs. Superheated Steam

When discussing steam boilers, it's important to understand the distinction between saturated steam and superheated steam, as each serves different industrial needs.

• Saturated steam is steam that is in equilibrium with water at the same temperature and pressure. It contains no additional heat beyond what's needed to convert water into steam. This type of steam is commonly used in heating applications and processes where direct contact with the product is required, such as food production or sterilization.
• Superheated steam, on the other hand, is produced by adding more heat to saturated steam without increasing its pressure. This results in steam at a higher temperature, which is ideal for driving turbines and other mechanical equipment. Because it doesn’t condense as easily, superheated steam is more efficient for energy transfer over long distances.

Understanding which type of steam your application requires can help you choose the right boiler and optimize performance.

Electric Boilers

Electric boilers are gaining popularity as a clean and efficient alternative to traditional fuel-fired systems. Instead of burning gas, oil, or coal, electric boilers use electrical resistance or induction to generate heat.

Key advantages include:

• Zero emissions at the point of use, making them ideal for facilities with strict environmental regulations.
• Compact design and quiet operation.
• High efficiency, often approaching 100%, since nearly all the electrical energy is converted into heat.

While electric boilers may have higher operating costs depending on electricity rates, they offer a low-maintenance, sustainable solution for many commercial and industrial applications—especially where fossil fuel infrastructure is limited or undesirable.

Making the Right Choice for Your Operation

Every boiler, whether firetube, watertube, steam, or hot water, has its unique strengths. The right choice depends on:

• Your unique operational needs; pressure requirements and steam capacity
• Facility size and available footprint
• Operator experience and maintenance resources
• Energy efficiency and emissions requirements

With modern advances such as ultra-low NOx burners, economizers, and Nationwide’s proven CataStak™ SCR System for near-zero NOx performance, today’s boilers are more efficient and environmentally friendly than ever before.

Whether you’re evaluating a firetube boiler for a commercial application or a watertube boiler for high-pressure steam production, understanding the differences between boiler types is essential for making the right investment.

For more details and guidance, explore our resource: What Boiler Is Best for You.

This article has been updated to reflect its original publication date of April 2019, while incorporating current insights and clarifications to ensure continued relevance and accuracy.

When selecting an industrial steam boiler, it’s essential to understand the key differences between saturated steam and superheated steam boilers. These two steam classifications play distinct roles across industries, ranging from heating processes to power generation. In this guide, we’ll explore the science behind saturated and superheated steam, advantages and disadvantages of each, and how to determine which type of boiler is best suited for your application.

What Is the Difference Between Saturated Steam and Superheated Steam?

Saturated steam is steam that exists at the boiling point of water and is in equilibrium with liquid water at a given pressure and temperature. It contains moisture and is often referred to as “wet steam.” Saturated steam is produced when water is heated until it begins to vaporize.

Superheated steam, on the other hand, is created by heating saturated steam beyond the boiling point without increasing pressure. Also known as “dry steam,” superheated steam has no moisture content, a lower density, and higher energy content. It remains in a gaseous state even as it cools, which makes it highly effective in certain mechanical and thermodynamic applications.

Common Industries and Applications for Each Steam Type

Both saturated and superheated steam boilers serve important yet distinct roles across industries, which is why Nationwide’s fleet includes both saturated and superheated steam boilers for rent and for sale. Each type has advantages and limitations, making them better suited for specific applications.

Saturated Steam Boilers

Saturated steam boilers are commonly used for processes that require high-efficiency heat transfer. Industries that frequently rely on saturated steam include:

• Food and beverage processing
• Sterilization in healthcare and laboratories
• Pulp and paper manufacturing
• District heating systems
• Chemical processing

Advantages of saturated steam include:

• Efficient heat transfer: Excellent for processes requiring quick, even heating.
• Simple temperature control: Steam temperature adjusts with pressure for consistent results.
• Compact equipment: High heat transfer rate requires less surface area, reducing system footprint and initial equipment costs.
• Reliable for direct heating applications.

Superheated Steam Boilers

Superheated steam boilers are ideal for applications that involve turbines or steam-driven mechanical equipment. Since superheated steam doesn’t condense into water droplets, it prevents corrosion and erosion inside critical components. Industries that commonly utilize superheated steam:

• Oil refineries and petrochemical plants
• Power generation (steam turbines)
• Large-scale manufacturing facilities
• Enhanced oil recovery and gas processing

Advantages of superheated steam:

• Zero moisture content: Prevents damage to turbines and piping.
• Increased thermal efficiency: More energy per pound of steam, ideal for power generation.
• Higher work output: Superheated steam can do more work before condensing.
• Extended equipment life: Reduced risk of corrosion and scaling.

While certain industries tend to favor one type of steam over the other, it’s important to note that specific processes may require the opposite—for example, some applications in saturated steam-dominant industries may still call for superheated steam. Ultimately, steam type should be selected based on the specific process requirements, not just industry norms.

Saturated vs. Superheated Steam: Which Boiler Do You Need?

Choosing between a saturated steam boiler and a superheated steam boiler depends on your specific process needs. For direct heating, sterilization, or process steam, saturated steam is typically the better choice. For driving turbines or maximizing work output from steam energy, superheated steam offers significant advantages.

Here are some important factors to consider:

Consideration	Saturated Steam	Superheated Steam
Heat transfer efficiency	High	Lower
Ideal use	Heating processes	Power generation
System complexity	Lower	Higher (requires superheater)
Energy efficiency	Excellent for heating	Excellent for turbines

Nationwide Boiler: Your Source for Rental & Mobile Steam Boilers

Nationwide Boiler provides high-performance boiler solutions for both saturated and superheated steam applications. Our rental fleet includes mobile boiler systems available for temporary steam needs and our in-stock inventory offers boilers for permanent applications, with capacities suited for industrial facilities of all sizes.

We proudly own and maintain:

• The World’s Largest 150,000 lb/hr, 650 psig Mobile Saturated Steam Boiler
• The World’s Largest 110,000 lb/hr, 750 psig Mobile Superheated Steam Boiler

And we continually stock what we’ve coined as the “World Boiler”:

• 200,000 lb/hr, 750 psig B&W Skid-Mounted Superheat Steam Boiler

Whether you need short-term steam supply or a permanent solution, our team is here to help. Visit www.nationwideboiler.com to explore our steam boiler rentals, request a quote, or speak with a steam expert.

This article was originally published in April 2019 and has been thoroughly updated to reflect current industry standards, enhanced technical explanations, and expanded application insights for both saturated and superheated steam boilers.

Companies require rental equipment for several reasons. By understanding the rental process and following the guidelines below, it is possible that the result will be both cost-effective and technically successful.

Steam Requirements - Up front planning is the most important stage when renting equipment. First, the maximum potential steam load needed must be calculated. Your steam requirement is expressed in either boiler horsepower (hp) or lb/hr (one boiler horsepower is equal to 34.5 lb/hr steam at 212°F).

Accessible Location - A location must be selected that is easily accessible for the delivery and setting of heavy machinery and one which has easy access to the building or equipment in which the steam will be required.

Utility Connections & Supply - Fuel, water and electric power connections must be easy to access and are of sufficient size to meet the needs of the rental unit. Typically, rental boilers fire natural gas, No. 2 oil, or heated No. 6 fuel. It is also important to make sure that there is sufficient fuel capacity to supply any existing units and a temporary boiler.

Equipment Supplier - When evaluating a supplier of rental equipment it is important to know if the company is a full-time, dedicated rental company with the experience, equipment and capabilities you require. In addition, the location of the company's equipment is important, helping to minimize transportation costs and travel time. It is also important to determine if the company provides start-up and installation services.
Here at Nationwide, we have boilers located throughout the United States and our service department is available 24 hours a day for technical support.

Reputable rental companies will provide complete drawings and equipment specifications in considerable detail. Such items include the total capacity and operating characteristics of the boiler, water treatment needs and requirements, emissions requirements, weather protection, performance testing, and ASME code requirements.

Proposal Evaluation - When evaluating a proposal, normal factors including payment terms, change-of-scope clauses, liability coverage, and transportation costs need to be addressed. A well written proposal should address the rate and term on the rental unit, freight costs, time and travel charges for technicians, and should specify appropriate responsibility for installation and removal costs. You should also get the warranty statement for the rental equipment.

Operating Permits - Before installation of the equipment can occur, it is necessary to arrange for any operating permits required from regulatory agencies. This includes special permits that may be required in those areas where emission limits are strictly controlled. Areas in California including the San Joaquin Valley and the South Coast require sub-10 ppm NOx requirements.

Nationwide Boiler took the lead in equipping our units with Low NOx burners and SCR systems (the CataStak). Users facing 5 ppm NOx can rest assure that we have an immediate solution.

Maintenance - To ensure continuous, safe, and trouble free performance of the unit, there are a number of regular checks and maintenance tasks which must be performed. It is important that a log sheet be kept on site for the recording of every routine check and maintenance items completed. Daily checks include an examination of all safety devices, followed by an inspection of the low-water cutoff during every shift. The entire system should also be checked for leaks and corrected immediately. The flame pattern of the burner must also be inspected to make sure the combustion devices are working efficiently. Moreover, proper boiler performance is highly dependent on following the proper feedwater treatment and correct blowdown techniques. Failure to maintain proper water chemistry is a major cause of damage to rental boilers and the single biggest rehabilitation expense.

Return Shipment - Lastly, there are certain steps that must be taken to ensure safe return of a unit to the rental company's facility. It is the responsibility of the user to have plant or local boiler shop personnel disconnect equipment after use, which includes draining and flushing all boiler lines with clean water to help minimize any chance of corrosion. A final check of the condition of the boiler should be properly documented, recorded and sent to the rental company once the equipment is shipped.

As long as you plan in advance, budget accordingly, verify connection sizes, address permitting issues, properly train operators, frequently monitor the feedwater quality, and take responsibility in maintaining the equipment once it is installed, you can be confident that the risks associated with renting equipment will be minimized and that your project will be a success.

To kick-off our ‘Boiler Basics 101’ series, we are starting at the very beginning. The extremely useful resource, produced by the commercial and industrial boilers that we rent, sell, service and maintain… that resource is steam.

Our business, and the boiler industry as a whole, revolves around steam. We provide boilers and related equipment for both temporary and permanent applications; equipment that works together to produce the valuable resource of steam, utilized in an abundance of processes across many different industries. So, what exactly is steam and what is it used for?

Let’s start with the chemical composition of steam. Water can exist in three physical states; solid, liquid, and vapor. These physical states, in more common terms, are referred to as ice, water, and steam. When water is heated at atmospheric pressure, its temperature rises until it reaches the highest temperature at which water can exist at this pressure. This temperature, 212F or 100C, is the saturation temperature, or boiling point. As water boils and temperature continues to increase, water particles begin to form small bubbles that rise to the surface and vaporize. This is how steam is formed.

Traditionally, steam was associated with locomotives and the Industrial Revolution. However, now steam is an integral part of modern-day technology. Not only is it an excellent source of energy and heat, but it is also sterile, which makes it ideal for use in the food, pharmaceutical, and health industries. Many other industries also utilize steam for processing, petroleum refining, utility and power, and manufacturing.

Steam has become an invaluable part of our world.  Without it, many of the advances and technologies in today’s time would not be as effective or efficient as they are now.

Stay tuned for the next article in our Boiler Basics 101 series to learn about the basic anatomy of a boiler system.