Breaking Down the Boiler Room Part 1: Boiler Basics

Based on the name alone, the term boiler should naturally make people think of hot water.

Yet people are often surprised to learn we work with boilers too. Maybe it’s because boiler technology has been around for so long and used for many different things in various ways over time (like powering locomotive steam engines!), that it’s hard to believe a boiler can still be a relevant piece of equipment in modern boiler rooms. But it’s true, boilers can still be quite useful today, especially when placed in the right circumstances.

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For the purpose of this post, we’ll skip the history lesson on boilers in general, and instead focus on the basics of how boilers are used today for space heating, water heating, and sometimes both.

You’re aware of the boiler in your building, but have you taken a close look at how a boiler system works? Technically, a boiler is an enclosed vessel or arrangement of tubes in which water is heated and circulated, either as hot water or as steam, to supply heat or power. So on a very basic level, boilers are the ultimate water heater. There are definitely similarities between a water heater and a boiler based on definition, internal function, and some shared technology, but there are also a few key differences.

Water heaters serve a distinct purpose: to produce and store hot water for domestic uses like bathing, washing dishes, laundry, food prep, etc. Boilers also produce hot water, but they can’t store it, and the hot water (and/or steam) they produce can be used for various purposes. Commercial boilers today are most commonly used for space heating but are also still used for domestic water heating, and sometimes both, with the right setup.


How Boilers Work

Boilers can be pretty complex pieces of equipment with multiple little components that can vary based on how they are being used. But regardless of end-use, the core concept of any boiler’s function is generally the same, so let’s start there.

Commercial boilers come in all shapes and sizes so it's important to know the hot water needs of your commercial businessCommercial boilers come in various types and sizes can range from 2’ by 2’ to over 5’ tall and more than 8’ long, depending on the application. Some boilers have a vertical configuration, so they are taller and slimmer to limit their floor footprint, while others are horizontal—short and wide.  From the outside, the boiler itself simply looks like a big box (though some boilers are still just cylindrical vessels). It has water connections, a ventilation flue and/or exhaust system, and a rust-resistant powder-coated outside. An operation status panel shows you the boiler is working. The boiler is connected to a fuel source to keep the flame burning inside.

The inside of a boiler is where it gets tricky to generalize because the mechanical guts and configurations tend to vary by type of boiler and by each manufacturer’s proprietary technologies. But regardless of type, there are two main elements inside nearly any boiler: the burner and the heat exchanger—the heart of your boiler. Usually categorized by the type of heat exchanger used, the most common boilers on the market today include water-tube boilers, fire-tube boilers, and high-efficiency condensing boilers.

A water-tube boiler contains the heat exchanger, a series of metal tubes through which water travels.For our purposes and to keep it simple, we’ll start with a very common type of boiler found in many commercial buildings, the water-tube boiler. In this case, the heat exchanger (also called the tube bundle) is a series of metal tubes through which water travels. Historically, these tubes have been mostly made of copper due to the metal’s natural ability to retain heat, while some models use stainless steel tubes for its natural resistance to corrosion. But many current boiler models now feature heat exchangers with tube bundles made of cupronickel, a strong, water-safe copper-based alloy blended with nickel and some other corrosion-resistant elements. Often these tubes are “finned” instead of smooth, to increase the surface area for greater heat transfer. Heat is generated by the aptly named burner, which burns a fuel such natural gas to produce a very hot flame that runs underneath the full length of the heat exchanger, surrounding the heat exchanger above with the hot combustion gasses produced by that flame, heating the water within. When the boiler turns on, a pilot assembly provides a spark, creating the super-hot flame along the burner that heats the copper pipes and the water within those pipes, resulting in very, very hot water or steam that provides heat for the intended purpose. (A fire-tube boiler is conceptually the total opposite of a water-tube boiler, so instead, the exhaust gasses actually pass through the tube bundle, which is surrounded by the water it’s heating.)


How Boilers Can Be Used

That’s how a boiler creates hot water or steam on a super basic level—what happens to that hot water from there differs based on how the boiler is being utilized. As we mentioned earlier, boilers work to heat water but don’t have the capability of storing hot water. So, when a boiler is being used to supply hot water for general use (known as domestic water heating), it must be connected to some other equipment that can store hot water, such as a storage tank (or multiple) or an indirect water heater. But modern boilers are actually most commonly used just for space heating (known as hydronic heating), so there’s no need to store the hot water because it’s sent out into the system to heat the building.

Space Heating – The Hot Story on Hydronic Heating

The boiler systems most frequently seen are called hydronic heating systems, and they only use hot water or steam to heat the air inside a space. The most standard method of hydronic heating makes use of radiators to distribute the heat. In a building or home with radiant heat, water is heated by a boiler to a point just below boiling and it runs through pipes and into radiators throughout the building, which then release that heat to warm the spaces and rooms in which they sit. In modern applications, radiant floor heating has even been developed, where tubing can be put in underneath the flooring with a similar effect. Super-hot water runs through the pipes that are inlaid in a floor, which heats the flooring material (tile is often used) and as the heat rises from the floor, it heats the room.

The water in these systems flows in a continuous loop from the boiler, to the pipes, to the radiators, then back to the boiler to be reheated. This is known as a closed system. The water in these systems is unrelated to the hot water that flows out of your faucet or into your washing machine—it is only used for heat. In fact, this water is not rated for human consumption. That doesn’t mean there’s anything wrong with it, it simply has other things to do, like being recycled back into the system to be reheated.

In space heating, a closed-loop system is much more efficient than always using a fresh new flow of water (aka an open system) to heat an entire building. Since this water stream never comes into contact with the potable water used for showering and washing, buildings with hydronic heating still require another separate piece of equipment for their domestic hot water—typically, it’s a classic tank-type water heater. Sometimes it’s an indirect water heater, but we’ll loop back to this shortly.  First, let’s talk about how else boilers are used unrelated to space heating, like those used solely to generate domestic hot water.

Boiler vs Water Heater – A Domestic Dispute

If there’s a commercial boiler in a building, but it’s not heating the building, then the boiler is likely being used for domestic water heating in place of multiple water heaters. In these cases, a hot water supply boiler is connected to a separate storage tank; water is piped into the building from the municipal water system and heated via the boiler. The hot water moves from the boiler into the storage tank or tanks, where it’s held until someone turns on a hot water faucet or runs a piece of equipment requiring hot water. You can think of a storage tank like a giant thermos; it is full of water that needs to be kept hot. The storage tank does not have the ability to heat water—only the boiler can heat the water.

So, if you still need a separate storage vessel, when and why would you use a boiler for your domestic hot water supply instead of just a tank-type water heater with built-in storage? Honestly, fully answering this question requires its own dedicated post. (So stay tuned for Part 3 of this series, when we’ll dive deeper into this hot topic!) But for now, we’ll go with a brief overview.

Sometimes, hot water boilers are necessary by default, when standard water heaters can’t be installed due to venting conflicts or space limitations. More typically, though, domestic hot water boilers are used when tank-type water heaters simply can’t make enough hot water fast enough to meet the demand required for the application. In short, sometimes you just need more power!

A domestic hot water boiler setup will often be found in larger hotels, for example, due to the sheer volume of hot water needed in hotels at specific times throughout the day. The more guests a hotel can accommodate at any given time, the more hot water the hotel will require to meet demands. With an 11am checkout time, a full hotel could have hundreds of guests showering consistently over a 3-hour timespan.  A few hours later, housekeeping will likely have a lot of dirty laundry to wash and sanitize. A single boiler with multiple storage tanks can ensure a large quantity of hot water is available when needed, without the boiler turning on every time a small amount of hot water is needed throughout the rest of the day.

A boiler has the capability of a much higher BTU input than a single commercial water heater, meaning multiple water heaters are required to match the hot water output of one boiler. As we mentioned earlier, the flame inside a boiler is very large and very hot—much larger than a water heater flame.  Remember, the biggest boilers can be over 8 feet long, which means they can contain close to eight feet of burner, or close to eight feet of flame. That gives boilers the capability to heat those copper pipes and the water contained in them very quickly, and this is part of what makes boilers with storage tanks a good choice for commercial applications that need a large volume of hot water all at once, like food manufacturing businesses, breweries, senior living facilities, or large hotels.

Another use for a hot water boiler system that’s worth mentioning is commercial pool heating. If your building or hotel features a pool, then using a hot water boiler is often the best choice for a pool heater, because the added power of a boiler is necessary for efficiently heating a large pool. Not only does the pool itself act as a storage tank (saving you money), but pool chemicals wreak havoc on the inside of a water heater causing premature failure. This chemical concern combined with the potential to overwork a standard tank-type water heater makes boilers the better choice for pool applications.

Doing Double Duty with a Combination Heating System 

We’ve briefly covered hydronic boiler systems (those used just for heat) and domestic boiler systems (those used just for potable hot water).  But what about a setup that uses a boiler to heat the building and provide domestic hot water to the building’s faucets and fixtures? This can be done by connecting a hydronic heating boiler with an indirect (or coil) water heater tank. This boiler + indirect tank system is known as a combination boiler system.

An indirect water heater is something in between a water heater and a storage tank. It’s similar to a water heater—it has its own separate cold-water inlet, getting filled with fresh potable water from the municipal system, but it lacks the mechanical guts to directly heat that water on its own. But an indirect tank is also more than just a storage tank because it does technically heat the water within it, just indirectly. Water and heating combination systems are becoming more popular because they can offer greater efficiency in the right circumstances.

An indirect water heater is kind of like a sidecar on a motorcycle, piggy-backing off the power of the primary appliance to gain a secondary bonus function. Indirect water heaters are installed beside and connected to a hydronic heating boiler via a secondary closed loop of pipe that’s full of boiler-generated hot water and runs from the boiler into the indirect tank. When that pipe gets inside the indirect tank, it connects to a heat exchanger, another copper pipe that’s twisted around like a corkscrew (or coil) inside the tank, and then it loops back out to the boiler. The heat is transferred from the boiler-heated water in that coiled pipe to the cooler water that is held within the indirect tank. (We usually say the term “hot water heater” is redundant but using hot water to heat other water means an indirect tank literally is a “hot water heater.”) As this process continues, all that water held in the indirect tank is heated up to HOT—and that’s the hot water that’s going to come out through your sinks, dishwashers, and faucets.

This type of setup comes with its own set of pros and cons that we can’t fully cover here, so if you’re looking for more details on this, check out Part 2 in our Boiler Room Breakdown series, where we really explore the ins & outs of Combination Boiler Systems and Indirect Water Heaters.


Boiler Considerations

Admittedly, this has been a rather generic overview of boilers and some of their modern uses today. There’s so much more information we could cover about boilers, but most of it is super technical and downright boring—and our goal is education, not sedation!  However, there are a few more factors about boilers still worth mentioning here: efficiency, safety, and longevity.

Efficiency Factors

Not all boilers are created equal. There is a multitude of subcategories of boilers based on function, fuel source, type of heat exchanger, materials used, etc. And just like with water heaters, technological advancements have allowed boilers to achieve increased efficiencies by maximizing energy use.

In the past, most boilers installed were atmospheric units, meaning they draw air for combustion from the surrounding atmosphere to feed their flame, and the exhaust gasses are vented out through a chimney. These types of boilers are considered to be “standard efficiency,” and are about 80-86% efficient. But newer boilers on the market today can offer high efficiencies of 95% and greater, thanks to a sealed-combustion condensing design that limits heat loss while maximizing heat transfer, and modulating controls that allow the boiler to fire at different levels. A modulating boiler’s controls will monitor the heat absorbed by the building by measuring the temperature of the boiler water when it leaves and again as it returns to the boiler. The larger the temperature difference, the more heat the boiler must add to the water. When the temperature difference is small, the boiler can remain at low fire, making these units much more efficient. Different firing levels can be accomplished in a number of ways, including varying the number of burners within the equipment or by varying the intensity of the flame by reducing fuel level or creating negative air pressure inside the unit.

Safety Factors

Just like water heaters can explode, boilers also come with that risk for the same reasons (thermal expansion, increased pressure, enclosed vessel). But because boilers are equipped with more power, they have the potential to make much a bigger boom. For that reason, most commercial boilers, regardless of use, require a permit to operate and an official safety inspection upon initial install before the permit is issued. These laws vary by state, and by size and type of boiler, to some extent. Most states also require regular periodic inspections to keep the permits renewed.  In Indiana, for example, boiler safety inspections are actually regulated by the IDHS (Indiana Department of Homeland Security), and many periodic inspections are performed by state inspectors and billed to the owner as a part of the permit renewal process. This is why it’s extra important that your boiler is regularly checked as part of a preventative maintenance plan and any issues are quickly addressed to ensure it’s always running safely.

Longevity Factors

So, what’s the lifespan of a boiler? Well, with a routine maintenance and service plan, a boiler can last a surprisingly long time. We’ve seen commercial boilers that have lasted for up to 30 years, but the lifespan of a boiler and its parts varies greatly based on a variety of factors. The type of application, water quality, weather conditions, housing environment, and regular maintenance all play a big part in the lifespan of a boiler system.

As with tank-type water heaters, it’s important to be sure your boiler and combined tank are using softened water. Sediment in the heat exchanger of a boiler can clog the tubes and inhibit the free flow of water. This may cause the boiler to bounce up and down, eventually causing the heat exchanger to give way, resulting in a leak from the heat exchanger that will a) extinguish the pilot assembly, putting a stop to all water heating capability and b) end up as a giant puddle on the floor of your building. Being careless about softening water can lead to the catastrophic failure of your equipment.

Every aspect of a boiler can be repaired or replaced, from the external sheet metal panels to the internal components, but of course, there are many times when a repair isn’t as cost-efficient as a replacement. Heat exchangers and other internal components may need to be fully replaced and depending on the type of boiler, replacing a heat exchanger could cost just as much as a new boiler.

Just as you should always call a trained technician to handle your water heater problems, you shouldn’t entrust your boiler repair to just anyone. The components of a boiler system may seem fairly simple to understand, but there are many critical pieces that must be in working order for the boiler to run smoothly and safely. It’s easy for an untrained eye to overlook something major, resulting in more issues down the road. Always use a professional to service and perform maintenance on your boiler and water heating equipment.

It’s important to understand the basics of boilers and water heaters so you make an informed choice. Don’t know where to start? Contact our trained professionals at Reliable Water Services (800-356-1444) to get the best recommendation for your business. We’re happy to help you choose the best water heating system for your commercial application.