I have an apartment with quite good sealing on the windows. Due to no window in the bathroom, there is a constant ventilation going on, sucking air from the bathroom (an therefore the apartment). There are some small holes by design in some of the windows sealing, to let air in to guarantee the airflow. I would like to know the following: Is the air pressure inside exactly what it is outside, even if the ventilation sucks a lot of air from the room? Or in other words, is the natural air pressure outside high enough and a few small holes enough to enable enough air flowing to keep the air pressure on the same level as outside?
No, the pressure is certainly lower. Its difference is the driving force that makes air pass through the aerodynamic resistance of the holes.
Interestingly enough, the very lowest pressure is inside the holes, where the air has highest velocity. But everywhere in your appartment, the pressure is lower than outside.