Kansas (913) 281-7200 || Oklahoma (918) 901-9332

Whether you’re a business owner or building manager, the world of commercial water boilers can be perplexing and intimidating. Although commercial boiler technology remains largely unchanged, there are numerous factors to consider and various commercial boilers available. Many business owners may find the decision-making process challenging.

In this article, we will walk you through everything you need to know about commercial boilers, including how they work, the differences between the types, how to maintain them, and how to identify when it’s time to replace yours.

The Basics About How Commercial Boilers Work

In their most basic form, commercial boilers are designed to convert heat provided by a fuel source, such as natural gas, propane, oil, or electricity, and transmit heat energy from one area of your facility to another. Essentially, a boiler is a pressure vessel that captures heat and transports it efficiently from the boiler room to the point of use.

This process can be completed in a variety of ways. Some commercial boilers, for example, use hot water directly, while others use water that has been converted to steam. Pipes then circulate hot water or steam throughout your commercial facility, where it enters radiators or other heat-distribution components. This provides the necessary heating to make your indoor work environment comfortable for employees, tenants, and visitors.

Depending on the application, commercial boilers can range in size from 2′ by 2′ to over 5′ tall and more than 8′ long. Some boilers are vertical, meaning they are taller and slimmer to reduce their floor footprint, whereas others are horizontal, meaning they are short and wide.

The Major Components of a Boiler System

Commercial boilers, like other types of HVAC equipment, are made up of several different components that play a vital role in distributing heat throughout a facility.


The burner is the part of the boiler where the air is mixed with a fuel source and generates the heat required to increase the temperature of the water inside the boiler. This component starts the combustion process, which is controlled by electronic commands from a thermostat and directs hot combustion gasses into the boiler.

Because the proper amount of combustion air is vital for clean and efficient combustion, this component of your boiler must be well maintained. Too little air in the burner prevents complete combustion, whereas too much air allows for excessive exhaust gas loss.

Combustion Chamber

The combustion chamber is where the fuel is burned to heat the water. The chamber houses the burners and provides a safe area for high-temperature volatile fuel combustion.

Combustion chambers are typically made of steel, cast iron, or other heavy-duty metals capable of withstanding temperatures of up to several hundred degrees. This component is another aspect of the boiler that must be serviced regularly, as older units can become corroded or cracked, rendering them unsafe.

Heat Exchanger

The heat exchanger is the component that transfers heat from the combustion chamber’s burners to the boiler’s water. The pressurized hot water is pumped to radiators or fan coils to provide space heating.

Heat exchangers can be made from various elements, such as bundles of steel tubes, cast iron, or copper lines. However, the parts must be made of a very strong material that can withstand high temperatures, last a long time, and efficiently transfer heat.


The boiler system controls allow users to set the water temperature, the air and fuel supply mixtures, the internal pressure, and the ignition. The controls also govern how frequently the burner fires, the quality of the fuel-oxygen mixture, the rate at which the fuel is used, and how hot the water becomes.

The controls are also an essential part of your boiler’s safety system. Uncontrolled, high-pressure steam can be extremely dangerous, and well-maintained system controls help keep your boiler completely safe by ensuring that internal pressures remain within a safe pressure and temperature range and the system continues to operate correctly.

Exhaust Stack

The exhaust stack, also known as the chimney or flue, is a series of pipes that transports exhaust gasses from your facility to the outside world. The exhaust stack must be carefully constructed to ensure that harmful gasses, such as carbon monoxide, are securely vented away from your facility’s interior. It is also crucial that they are not built so that powerful wind downdrafts can re-enter your property.

Supply Lines and Return Lines

Supply lines run from the boiler and deliver heated water or steam to distribution points, such as radiators or heaters, throughout your building. When the water at these points cools or the steam cools and converts back to water, the return lines bring it back to the boiler to be reheated before being sent out again.

Circulator Pump

Lastly, the circulator pump pushes hot water through the supply lines to the radiators or other distribution lines. The circulator pump is also in charge of bringing it back through the return lines. As a result, the circulation pump is critical to the operation of your boiler and must be well-maintained to ensure that the system runs as efficiently as possible.

The Different Types of Commercial Boilers

Commercial boilers are classified into several types, each providing its respective benefits and advantages. Understanding the various types of boilers will assist you in determining the criteria that best suit your company’s specific requirements.

Condensing Boilers

Condensing boilers use a heat exchanger specifically designed to lower the temperature of the flue gas, allowing it to condense and absorb the extra energy from condensation. Condensing boilers have an extremely high thermal efficiency of up to 98% due to the condensing of water vapor in exhaust gasses.

Electric Boilers

Another type of boiler commonly used in commercial applications is the electric boiler. Electric boilers are highly efficient and environmentally friendly because they generate heat without using fossil fuels. Because there is no need for fuel combustion, electric boilers have no exhaust stack, no fuel handling equipment, and no fuel sources, resulting in minimal complexity.

Firetube Boilers

Firetube boilers employ a cylindrical vessel with the combustion gasses contained within the tubes and the flame in the furnace. The vessel houses not only the tubes and furnace but also the steam and water.

Because a typical firetube boiler has a simple design and requires less maintenance than a watertube boiler, these types of boilers provide a cost-effective heating solution and are frequently used in smaller industrial facilities that require lower operating pressures.

Watertube Boilers

Watertube boilers are designed to circulate water that is externally heated, with hot combustion gasses moving between the water-filled tubes. The expansion of heated water causes this excess volume to be transferred into an expansion tank, where the water cools and returns to the boiler to be reheated as the heat is radiated. These boilers have a higher capacity and can handle higher pressures and temperatures than firetube boilers.

Watertube boilers are typically classified as the following.

A-Type Watertube

A-type boilers have two mud drums located on the outside walls and a single centrally located steam drum with the burner on the centerline.

O-Type Watertube

A single centrally located mud and steam drum with bent types on either side and the burner located on the centerline of the steam and mud drums are used in an O-type boiler.

D-Type Watertube

A D-type boiler has a single mud and steam drum on the left or right side of the boiler, as well as a large bent tube configuration with the burner located out to the side, away from the mud and steam drum centerlines.

Flexible Watertube

A flexible watertube boiler is similar to an O-type boiler, but it has a much more complicated tube bend configuration to allow for a more compact design, multiple pass flue gas flow, and thermal shock resistance.

Signs It’s Time to Replace Your Commercial Boiler

Like any commercial HVAC system, boiler systems should be serviced at least once a year to ensure they’re working efficiently and avoid future breakdowns or costly repairs. Because boilers can be used for a number of applications within a commercial building, it’s crucial to make sure they’re working efficiently and at full capacity.

Luckily, there are many ways to ensure your commercial boiler remains fully operational. Here are a few signs to pay attention to that will help you avoid costly boiler repair in the future.

Age of the Boiler System

Even the best commercial boiler is not indestructible. Though commercial boilers are designed to last between 10 to 15 years, they are likely to become less energy-efficient as they age. If you know your boiler system is nearing the end of its lifespan, it may be time to consider an upgrade before it completely fails.

Increased Energy Expenses

If you begin to notice higher-than-usual utility bills, it’s possible that your commercial boiler is not operating at full capacity. In some instances, this may call for a minor repair or a complete boiler replacement. Although maintenance and repairs can often help, it may be time to upgrade if you find that service calls are becoming common.

Strange Noises

If the boiler in your commercial building has ever startled you with loud noises, this is not normal. Boilers make noise, but if you hear loud bangs or clanging, you should have it inspected at your earliest convenience. Loud noises usually indicate a blockage or an issue with water pressure, but the only way to be sure is to have it inspected by a trained technician.

System Leaks

Commercial building owners and facility managers should keep an eye out for leaks, which could indicate that it’s time for a new boiler. While leaks can often be repaired, avoiding the need for a complete replacement, it’s critical to have them inspected if you notice excessive leaking.

Hot or Cold Spots

Lastly, an older commercial boiler may heat areas unevenly at different times of the day. If you notice that some regions of the building are hotter than others or that temperatures vary throughout the day, it may be time for a replacement.

Contact Design Mechanical Today for Commercial Boiler Service You Can Trust

If you’re looking to get the most out of your commercial HVAC equipment or think it might be time to upgrade your existing equipment, look no further than Design Mechanical.

Our team has over 20 years of experience in 24/7 commercial HVAC services, and we remain committed to being the number one choice for our Kansas City customers. Our team of over 100 HVAC service experts is ready to assist you with all your repair and maintenance needs. Contact us today to schedule a free consultation and learn how we can help.