That’s the common misconception. The lines running between minisplit units are for refrigirant, not air. It’s essentially a fridge without a box, with the room where theyre mounted becoming the box instead.

You’re right I was wrong about that, sorry lol.

It doesn’t. It’s just that people who run AC’s usually shut everything closed and then exhale all that co2, which in an ordinary room with just 1 person in takes <1hr to reach noticeable impairment levels. AC or not, ventilation is important.

You might be right but I am certainly not opening my windows once an hour during winter, if that’s the standard then we’re all screwed by the time we go to bed with the windows closed. I don’t think this problem is significant enough to justify running an Air Conditioner with the windows open…

You’re probably thinking about carbon monooxide, not carbon dioxide?

Yes, I am. As that is the only “real” concern I see with AC’s and gas buildup. As I said co2 is just not a big enough issue to justify not getting an AC or letting it run out the window. Regularly airing out should be common sense, but I think once or twice a day is regular enough for the average apartment