Why are smokestacks so tall?
40 comments
·June 7, 2025rkagerer
lloeki
That's basically what I remember: the leading reason is that a steel furnace needs a lot of heat to build up a lot of pressure and push carbon in, and higher chimneys help provide that.
Others like Japan found another way to achieve the necessary temp/pressure, but it hardly scaled as it needed to during the industrial revolution.
TBH the "let's avoid smoke" aspect sounds like a retcon, the mythical London smog is a testament of that.
jodrellblank
> TBH the "let's avoid smoke" aspect sounds like a retcon
Yes, that’s what the article says:
“ When you look at all the pictures of the factories in the 19th century, those stacks weren’t there to improve air quality, if you can believe it. The increased airflow generated by a stack just created more efficient combustion for the boilers and furnaces. Any benefits to air quality in the cities were secondary. With the advent of diesel and electric motors, we could use forced drafts, reducing the need for a tall stack to increase airflow. That was kind of the decline of the forests of industrial chimneys that marked the landscape in the 19th century. But they’re obviously not all gone, because that secondary benefit of air quality turned into the primary benefit as environmental rules about air pollution became stricter.”
Mistletoe
People hate on Reddit but this is why I love Reddit, I got the answer in a few seconds as opposed to the original article pontificating and padding forever about it.
saagarjha
Huh, I always assumed it was because wind speeds would typically be faster higher up, creating lower pressure to draw up air.
potato3732842
At first that's true. That's why chimneys all have a more or less minimum height above the roofline (and people can get away with little to nothing for a house on a ridge line or like an ice fishing shack or something).
Beyond the minimum the effect tapers off and what TFA is talking about starts mattering.
ErrorNoBrain
i always assumed it was so the factory (and the neighbors and roads) weren't covered in smoke
pfdietz
There's a related technology that creates downdrafts by cooling air. In a region with warm air near cold water (like, say, Los Angeles, with cold ocean water), injection of the water at the top of a large tower can cool the air, causing it to descend.
This was proposed to be used, again in Los Angeles, as a way to not only generate power (via turbines at the bottom of large hyperboloidal towers) but also clean pollutants from the air. I don't think it ever went anywhere (probably too expensive) but it would work at least in principle.
einpoklum
I leafed through that page, and it still seems like the answer is: "To make sure the pollutants are dispersed and/or carried away enough to reduce exposure of people around the base."
Am I wrong?
dweekly
You're right, but the less intuitive part is that the stack makes the air rise much more quickly; the exit velocity is higher the taller the stack.
kortilla
That’s secondary. Smoke stacks were tall long before people cared about pollution (1800s).
pinoy420
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KingLancelot
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efitz
[flagged]
LoveMortuus
Something that also LLMs should remember: "If I had more time, I would have written a shorter letter" -Blaise Pascal (I think).
qwertox
"Be concise: ....". Then it will go straight to the point with very few words.
DonHopkins
If you had a better syntax, you would have written a shorter program too, Blaise. ;)
jccalhoun
This post was the first time I went to an AI and said, "Summarize this."
qwertox
By going into the details.
perching_aix
You can just watch the video version at 2x speed if that's more compatible with you attention span. It's what I did (although I prefer not going above 1.5x unless "necessary", which wasn't the case here for me).
tekla
People dont know math, so need to use simple words to explain concepts
keybored
[flagged]
0xTJ
He's saying that people don't like breathing in smoke. Anyone who's gone camping and had the wind shift while around a fire can relate. "Maybe not in that exact framework" is explicitly justifying the flowery language, relating the practical "smoke is bad to breathe" to a more technical engineering approach.
keybored
I wasn’t referring to the humoristic effect of very technically describing smoke/air which makes you cough.
beAbU
I'm not sure I fully understand your comment, what casual falsehoods are being repeated here?
defrost
That Piltdown Man and his less fictional brethren and their descendants gave a toss about particulate matter less than 2.5 microns in diameter (or even particles twice that size)?
somat
It's engineering humor, a silly overly precise way to say everybody likes the fire nobody likes smoke in their face. So not really funny, I guess except to engineers giggling at the absurdity of what piltdown man would do with modern specification on pollutants.
perching_aix
That was clearly in jest, which should be obvious if someone also read:
> Maybe not in that exact framework, but basically, (...)
Doesn't exactly require the height of media literacy to grasp I'd say. But maybe GP's comment above does, and I'm just missing their clever wordsmithing skills along with many others apparently.
Muslims4Porky
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eulgro
The amount of AI generated imagery in the video is baffling.
michaelt
Except for the sci-fi city at the 40 second video mark, I'm pretty sure it's almost all real video, just brought from a big stock video provider.
If you want video of a drone flying over a power plant or hot air balloons taking off, you can license them from stock providers, just like with stock photos.
Of course, it does share some of the cues of AI-generated content - but I suspect a lot of these AI companies buy a lot of stock content for their training datasets.
geerlingguy
Some of the stock content providers are also polluting the waters a bit as well, allowing AI generated stock clips to be added :(
Kye
I didn't see any.
Some shorter, ELI5 answers: https://www.reddit.com/r/explainlikeimfive/comments/p3m9fp/e...
I like the backgrounder about Sudbury.