Let us remind you that most air conditioners do not provide an inflow of fresh air (oxygen), but only make sure that the room is kept at a constant temperature. Pros and Cons of such devices are obvious: on the one hand, a user can be sure that the room will be exactly the temperature he/she set at the conditioner. On the other hand, the risk of being in a stuffy (though comfortable in temperature) room increases. After all, a conditioner can work properly only when the windows are closed.