@GoblinCookie
I disagree that pumping more smoke into the air is in any way more efficient or breathable. Economies of scale will reduce some of the waste, but it won't surpass the savings of several tiny fires in the same room. The ventilation needs to work regardless of hot smoke, or they're all going to die of CO2/CO poisoning.
It is not a question of agreeing of disagreeing it is a question of the basic laws of physics. I agreed that for a smaller number of dwarves, having several small fires (in effect them individually smoking) is more efficient, but as the number of dwarves in the room at the same time goes up, things switch over.
We'll assume the smoking room is surrounded by air-tight doors (a basic addition for when ventilation is a thing), so we don't have to worry about the smoke of C02 getting into the rest of the fortress. It is built around a chimney, according to rather the same setup as for forges really. The dwarves smoke in the room and the smoke exits through the chimney, without affecting the rest of the fortress.
One of the main issues with the ventilation is very much hot smoke/cold smoke. If you have cold smoke it will hover around in the air until it eventually settles down over everything as soot. This soot is an issue that requires cleaning up, but the greater the relative surface area of something the slower it cools down; no logical reason smoke is an exception. That means we will have less soot if we combine all our smoke into one single cloud than if we have an equivalent amount of smaller clouds, since less of it will cool down and fall as soot with less relative surface area.
If you think of the smoke mechanics like this. When the smoke leaves the fire, it is all hot and it heads upwards as a single mass. As the cloud cools down it does so at the edges, causing cold smoke to seperate be left behind. In a similar fashion to dust, the particles in the cold smoke are heavier than the surrounding area causing them to fall to the ground as soot. The aim of dwarven chimneys is for as much of the smoke to reach the surface as quickly as possible so as little of it lingers as cold smoke and turns into soot inside the fortress.