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Why are smokestacks so tall?

https://practical.engineering/blog/2025/6/3/why-are-smokestacks-so-tall
96•azeemba•11h ago

Comments

ErrorNoBrain•4h ago
i always assumed it was so the factory (and the neighbors and roads) weren't covered in smoke
rkagerer•4h ago
Some shorter, ELI5 answers: https://www.reddit.com/r/explainlikeimfive/comments/p3m9fp/e...

I like the backgrounder about Sudbury.

lloeki•3h ago
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•9m ago
> 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.”

keybored•4h ago
> From the time that humans discovered fire, we’ve been methodically calculating the benefits of warmth, comfort, and cooking against the disadvantages of carbon monoxide exposure and particulate matter less than 2.5 microns in diameter… Maybe not in that exact framework, but basically, since the dawn of humanity, we’ve had to deal with smoke one way or another.

Of course the intent here is exposition and not to allude to something that really happened since the dawn of time. But these casual falsehoods is how ideology is reproduced.

beAbU•3h ago
I'm not sure I fully understand your comment, what casual falsehoods are being repeated here?
defrost•3h ago
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)?
perching_aix•2h ago
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.

somat•2h ago
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.
0xTJ•2h ago
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.
efitz•3h ago
OMFG how can one take so many words to explain such a simple concept?
qwertox•3h ago
By going into the details.
LoveMortuus•3h ago
Something that also LLMs should remember: "If I had more time, I would have written a shorter letter" -Blaise Pascal (I think).
qwertox•2h ago
"Be concise: ....". Then it will go straight to the point with very few words.
DonHopkins•1h ago
If you had a better syntax, you would have written a shorter program too, Blaise. ;)
perching_aix•2h ago
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).
saagarjha•2h ago
Huh, I always assumed it was because wind speeds would typically be faster higher up, creating lower pressure to draw up air.
eulgro•1h ago
The amount of AI generated imagery in the video is baffling.
Kye•31m ago
I didn't see any.
einpoklum•26m ago
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•15m ago
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.

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