Ok, I have an interesting question: I recently purchased an 850 square foot condo. I have central air and was wondering if it is wise when having the central air on(with all the windows and doors shut of course), on at the same time I have my microwave exhaust fan on. I mean, with the a/c, you got positive pressure. With the microwave exhaust fan, or, bathroom vent, etc…, you got negative pressure. So, positive and negative pressure at the same time? Very curious here. Thanks, Martha