How do you decide where to locate vents, how large they should be, where to locate input and output vents. I've been researching this subject myself but don't feel much closer to an answer, and can't decide whether I'm overcomplicated the topic, or whether it's an engineering topic which I can't easily deal with well myself. I have read that Sip construction needs more ventilation than just opening the windows. This is for a 70m2 apartment in sunny Lisbon, Portugal.