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:

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.

At the end of a rental boiler project, proper decommissioning is key to ensure safe transport back to the rental boiler supplier and to avoid any unforeseen costs. It’s not just about disconnecting and moving the equipment - taking a few simple precautions can prevent potential damage and ensure everything is ready for return. Review and follow the steps below for a smooth, hassle-free pick-up and return of your rental boiler equipment.

Drain & Flush

Start by thoroughly draining and flushing all the boiler lines with clean water, making sure all water drain valves are fully opened. This step helps eliminate any remaining water that could cause corrosion or freeze damage, potentially harming the system during transport or storage. Flushing the lines also removes debris and buildup, improving the boiler’s performance for future use.

Inspect

Next, take the time to carefully inspect both the fireside and waterside surfaces for any visible damage, scale buildup, or issues with the refractory lining. These areas are crucial to the boiler’s efficiency, and any damage or buildup could lead to serious problems later. It’s also a good idea to take clear photos of the boiler’s condition at the end of the rental period. This way, there is a record to reference in case there are any questions or concerns about its condition when returned.

Equipment Prep for Removal

The stack and other components that were installed upon arrival to the jobsite should be removed and mounted back on the rental boiler trailer and/or shipping skid. Be sure to securely bolt the stub stack, non-return valve, safety valves, and vent valve back into place, just as they were when the equipment was delivered. Aligning everything properly ensures that each component stays in place during transport, avoiding movement or potential damage.

Additional equipment prep should be completed as follows:

1. Cover all boiler openings: this includes the stack, steam, gas, and water connections, electrical panel, and safety valve openings.

2. Reattach running gear and gooseneck: If the trailer was taken apart for transport, ensure that the running gear and gooseneck are properly reattached before moving the trailer.

3. Check tire pressure: Before transport, it's important to check the tire pressure of the trailer. Make sure the tires are inflated to the manufacturer’s recommended levels for optimal performance and safety.

By following these steps the return process becomes seamless, protecting the rental boiler, feed system or auxiliary equipment and ensuring that everything is handled properly from start to finish. If you have questions about preparing for the return delivery of your rental boiler equipment, don't hesitate to call Nationwide Boiler at 800-227-1966.

Reliability and Versatility of Nationwide Boiler’s Rental Fleet

Nationwide Boiler operates and maintains one of the largest and most versatile rental boiler fleets in the industry. Our purpose-built rental inventory includes over 100 temporary boiler systems ranging from 47.5 HP to 200,000 lb/hr, stored in multiple locations across the country. We offer multiple configurations including complete mobile boiler rooms, trailer-mounted watertube and firetube boilers, skid-mounted systems, factory-integrated skid packages, fully electric boiler systems designed for zero-emissions operations, and a suite of boiler auxiliary equipment options. This diverse inventory allows us to respond quickly and effectively to emergency outages, planned maintenance, or increased seasonal demand.

Reliable Steam Solutions for Diverse Industries

One of the key advantages of renting from Nationwide Boiler is our ability to provide fast, reliable steam solutions that are tailored to your application. Whether your facility requires low or high capacity, saturated or superheated steam, boiler-only or a complete temporary steam plant, our rental boiler fleet is engineered to support continuous, dependable operation. Our solutions support a wide range of industries including food processing, petroleum and chemical refining, power generation, pulp and paper, manufacturing, and more.

Maintenance and Refurbishment of Rental Boilers

As with any heavily utilized piece of equipment, rental boilers often return to our shop in need of service. Not every rental requires major repairs, but every unit goes through a standard inspection and maintenance process before being returned to service. Our skilled technicians perform routine tasks such as gasket and valve replacements, tube brushing, burner tune-ups, and safety control testing to ensure each system meets the high quality standards we’ve set over the years. These preventative and corrective measures address normal wear and tear that naturally occurs over the course of a rental. Having a disciplined approach to maintenance helps us minimize future service calls, ensure performance reliability, and reduce the total cost of ownership for our customers.

In rare cases, a unit may be damaged beyond repair and must be retired from service. However, thanks to our experienced fabrication team and dedicated Quality Control Department, most boilers are restored and returned to service in like-new condition. With proper maintenance, boilers can provide reliable performance for decades.

Why Retube a Boiler?

A complete boiler retube is one of the most effective ways to extend the life of a heavily damaged boiler, particularly in demanding industrial environments. Over time boiler tubes naturally wear down due to constant use, high temperatures, and exposure to impurities in the water. However, the lack of proper maintenance and water treatment can quickly accelerate this, leading to major damage to the internal boiler tubes and creating an immediate need for retube or complete system replacement.

When boiler tubes become corroded or damaged, overall performance, efficiency, and safety can decline, causing costly downtime or even system failure. Retubing restores the boiler’s internal components, significantly improving efficiency and returning the system to like-new condition.

A Commitment to Reliability, Sustainability, and Performance

At Nationwide Boiler, we take pride in our ability to perform quality service and maintenance on our rental fleet, as well as refurbish and repurpose equipment whenever the need arises. Retubing not only extends the useful life of our boilers but also plays a key role in our sustainability efforts. Instead of scrapping boilers that still have a solid pressure vessel and frame, we focus on restoring their core components. This approach reduces waste, conserves resources, and helps us maintain a high-quality, cost-effective rental fleet.

Our commitment to maintaining a high-performance rental boiler fleet ensures that our customers receive dependable, code-compliant, and cost-effective steam solutions every time. Whether you need a short-term rental for a few weeks or a long-term solution for several months, Nationwide Boiler has the equipment, expertise, and service to keep your operations running smoothly.

This blog post was originally published in June 2021 and has been updated to reflect the latest advancements in boiler maintenance, sustainability practices, and the continued expansion and modernization of Nationwide Boiler’s rental fleet.