This may seem like a question even grade school science classes have been answering forever. Everybody knows that warm air is less dense than cool air.
But why wouldn't it slow down as it goes up a taller chimney and cools? Even an insulated chimney cools air progressively and at the very least you'd think it slows down slightly more, rather than speeds up as you increase height.
And even though I can understand that warm air in contact with cooler air would tend to rise, in a chimney it is in a tube, separated from the cold air. So how can its non-contact surroundings affect it except at the top, where it comes back into contact with cool air.
If the answer to that is there is a vacuum created at the top when it suddenly cools, why would that increase dramatically with small increases in chimney height?
And why do we assume that exhaust from a fire is less dense than air, anyway? It has a lot more in it, creosote, water vapor, and soot, to name a few things. I mean maybe it is but at the chimney top where it cools what is its density?
So altogether what is really happening in a chimney as you increase the height?
On the net a bunch of searches all yield the same non-answer that warm air is less dense than cold air.
Yes, I register,
and........?