What is a Boiler?

what is a boiler

Cutaway of a boiler.

Boilers are everywhere behind the scenes doing tons of work. Work that most people don’t even know goes on.  Boilers and diesel generators in the submarine Navy get women’s names because you have to treat them like hard working women.

Boilers heat, clean, pump, sterilize, move aircraft carriers and launch the jets that take off from them. In another application, a boiler can distill water. There aren’t too many real boilers left out at sea as most have gone nuclear. Instead of combustion though, those simply use nuclear fission as the heat source and the devices are called steam generators rather than boilers.

Boiler relief valves.

Boiler relief valves.

Out in the commercial world, we mainly have boilers. And you know, I never even saw a real boiler until my 3rd civilian job. Before that I had never even needed a boiler’s license. When I got to that job as like a start-up engineer, I barely even knew what I was looking at. The guy was like “well, here are your boilers.” “Where?” I said. “Oh you mean these 3 black squares?” Yep, that was them. A black square just sitting there, each one about the size of a small car. These were package boilers.

I was used to seeing big monstrous steam generators and just figured boilers would look the same or close to it. Then come to find out these were package boilers and didn’t look like the rest. So today, just a brief overview of what exactly a boiler is, some of the things they can do, and maybe some other stuff.

Why it’s important

All engineers should have some knowledge of the principles of combustion, how combustion occurs in a boiler, and the combustion requirements for operating a boiler more efficiently.

What is a boiler?

From the book, High Pressure Boilers – 4th Edition, a steam boiler is: a closed vessel that contains water.

CLOSED vessel, very important. And this is also why we started earlier with the fundamentals of engineering posts. The Laws. Boyle’s and Charles’ right? Pressure, temperature. Boilers use a closed vessel in order to manipulate that pressure. If we can control that pressure, we can control that temperature right? Or vice versa? It’s alive! Without a closed vessel, the magic ain’t happening. Or it will be a lot more difficult to control.

boiler steam piping

Steam piping
(from wired.com)

And also – we must consider ALL of the steam piping, where this stuff goes to do work, as part of this closed vessel in a way. Because like the post yesterday about the laws of conservation of energy and matter – energy in = energy out.

If we are losing energy somewhere down the line, say like out of a small leak from some steam valve, not only are we losing steam pressure there but we are also not getting that steam back as condensate to do more cycles of work. We are going to have to EXPEND energy now, as a system, to add more water back, heat that up, convert it to steam, etc.

If we have a perfectly sealed, and operational “closed vessel” we would never have losses to make up for, pressure would be easily maintained. But of course thigns are going to fail, valves are going to break, etc. Building engineers.

Back to the definition or purpose of a boiler

Water in a steam boiler is pressurized and turned into steam when heat is added. When you burn a fuel, like natural gas, the chemical energy in the fuel is converted into heat. When the water boils and becomes steam, that same heat from the fuel is now contained in the heat of the steam. Never thought about that now did you? Friggin’ awesome.

What can these ladies do?

More like, what can’t they do? Besides move submarines the size of 2 football fields? Or aircraft carriers the size of a billion football fields (not really.)? Or make the steam that launches jets off of the deck of a carrier in less than a couple hundred feet? How fun would that be?

If you watch the 1:00 video, you can see the steam escaping from the catapult after the takeoff assist.

Heating – low pressure steam from boilers usually makes its way to hot water heat exchangers that heat water. This specific water then flows up and through the HVAC systems, heating the air that is passing through the ducts.

Electricity – boilers can be used to generate electricity. They can turn turbines (like in dams) that have shafts connected to power generation means – rotors/brushes/magnets.

Sterilize – in hospitals sometimes the boilers deliver steam to the central sterilization area. All of the fancy, shiny. horror movie creepy stainless steel tools they use to cut you open are put through vicious steam cycles in order to sterilize them.

Hot water – More steam goes to different hot water heaters which use that heat to make different water hot for drinking, bathing, your foo-foo coffee drinks.

what does a boiler do

Falling water generates tons of electricity.
(pic from water-technology.net)

Work – As shown by the Naval vessels above, boilers and steam can also move stuff. But I think the first steam boiler was used to pump out a coal shaft. This guy had water or something filling up his mine so he devised this boiler pump thing above ground that moved water from the bottom of the shaft to somewhere else. He built a boiler below the end of a sealed piston. As the steam was generated, the piston would be driven up. The steam would cool and condense, the piston would drop. When the piston dropped above ground, this guy had it piped to draw a suction on the mine bottom, thus drawing out the water in a pumping fashion.

Humans are smart creatures no? I saw that just now on Wiki, and I paraphrased it greatly.


If you’re a building engineer, you probably already knew that boilers did all this awesome stuff. If you’re a desk jockey maybe you didn’t but wondered how your office space got warm. Ultimately it was probably a boiler of some sort way down the line. Boilers are workhorses, are vital to the simple day -today operation of everything that goes on in most commercial buildings.

Can you imagine what would happen if an awful winter hit NYC, and say the buildings of Wall Street had zero heat? Or operating rooms where surgeries take place, without boilers humming along in the background? No sterile instruments, maybe improper heat in the space, no hot water for the medical personnel to scrub up with.

Next time you are out in an office space, take a moment and pay respect to the almighty boilers in the background.

Look, if you like this style of writing and learning, and want to stay on top of posts like this, you may want to consider subscribing. There is a tab up top I believe. I generally send out 1 email/week only linking to the latest training post, Sunday’s at 7pm my time. That’s it. Got an idea or comment? Let me know.

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