One Oven for Meat and Milk

And Levi said: Even lean kosher meat that one roasted with fatty non-kosher meat is permitted. What is the reason? It is merely an aroma, and an aroma is nothing significant. The Gemara relates that Levi took action, meaning that he put his opinion into practice, in the house of the Exilarch with a kid and something else, i.e., a pig, that had been roasted together. Levi did not prohibit the meat of the kid due to the aroma of the pig.

...Even though the Machlokes goes like Rav the halacha is like Levi

...It does not appear to me like Rebbe that it should be assur since there is a lot of space in our ovens and the air dissipates.

Do not roast kosher meat with non-kosher meat or meat of an unclean animal in the same oven, even if they do not touch one another. But if you did roast them, this is permitted - and even if the piece of forbidden meat was very fatty and the piece of permitted meat was lean. But if the oven is large enough to hold 12 esronim, and its mouth is open, then it is permitted to roast them in it as long as they do not touch one another. And if one of them is covered with a bowl or with dough or the like, it is permitted to roast them, even in a small oven with a closed mouth. Comment: The same is true for meat with milk - the ruling is also thus. And it is customary to be strict before the fact, even with a large oven, and after the fact to be lenient even with a small oven. But, if one baked a loaf of bread with meat, it is forbidden to eat it with milk if he has another loaf. And thus if an idolator baked a loaf of bread with something prohibited, it is prohibited to buy that loaf if he has another loaf - because all this is an instance of "before the fact." But if he has no other loaf available, both are permitted, because this is an instance of "after the fact." There are some who say that we do not permit on the basis of smell not being an issue, even after the fact, unless the oven is open from the side or above where the smoke can escape. But in a case of financial loss we are not stringent after the fact, even if the oven is completely closed. If the prohibited thing is pungent, and all the more so if the permitted thing is pungent, smell is an issue and even after the fact it is prohibited, if the two of them are uncovered. But if one of them is covered, even as is common with dough, it is permitted.

A pan of milk, placed in an oven, underneath a pot of meat - the steam rises, enters into the pot, and renders it forbidden. Rema: If there was actual milk in the pan, then we require sixty times its volume in the meat. All of this is when the pan is open, and the steam rises up from the food itself, to the pan that is above it, and also if the two are so close to each other that the steam that rises is so how that it would make your hand retreat rapidly. If not, then everything is permissible. Therefore, we hang meat (slabs) over dairy pots, and we don't worry about the steam that rises. And if something is covered, then everything is permissible, since it is like two pots that touch each other, which do not make each other forbidden, and all the more so with mere steam. But ideally (lechatchila) one should be strict on all this.

Source of Zeah is Mishna in Masechet Machshirim (2:2), which says that the steam that comes from a tamei bathhouse is itself tamei. We see from here that the steam that rises from something maintainsthe status of the item from which it came from. Therefore steam that comes from meat will be meat.

...But is an open space like in our ovens today, the steam goes up and does not osser the pot next to it...

...this is specifically with steam from liquids.