slight negative pressure is a guarantee against any smell escaping and that is all, it is a sort of barrier against going into slight positive pressure which would result in a smelly hissing and ballooning tent, after all do plants grow in a negative atmospheric pressure outside, and there is no law that states you must use an inlet fan to provide fresh air in your grow room, it is the exhaust that is the important factor, the only way i know that you can get near normal pressure is to use 1 exhaust fan and an opening somewhere in your tent/growroom at the bottom that the exhaust fan negative pressure would use to suck air in, after all they only use one fan at the top and one grill at the bottom of a hot damp shower room, but this opening would have to start small and be made larger every few minutes until you get a good balance of slight negative pressure, this is called a passive air intake, if you covered it with grill and fly screen then no large or small insects would be sucked in, and if your exhaust fan is on 24/7 then how can you get a smell outside your growroom from a passive vent that is sucking all the time, (when you use a carbon filter on your exhaust fan, that inhibits the air that the fan is allowed to push or pull out so any inlet fan that you do use has to be smaller or turned down using a fan speed controller), i have never seen a grow tent never mind used one but the facts speak for themselves, i only use prepared grow rooms, and prepared grow houses. but over the years i had to experiment but you can cram a lot of experience and experimental time in to a few months, if you are commited to learning. and google is your friend. i was inside a totally sealed growroom even the door has a seal, and i locked the door and turned the 1015cmh inlet fan on to full power the exhaust fan had not been fitted yet, the fan sounded like a minature jet engine, and after about 10 seconds the fan started to labour and after 20 seconds it was struggling and a strange muffled noise like the lady upstairs vacuming her carpets could be heard, i thought the fan was going to break, but then i felt a weird popping feeling in my ears and head and i felt giddy so i opened the door and the outrush whoosh of air was incredible i sat down in the hallway for a few minutes but i felt really weird for that few minutes, when i re-entered the room to turn the fan off to curb the fan noise from the open door it was as cold as a fridge as the air is sucked straight from outside, i know they use positive pressure in hospitals and laboratories and very ill patients rooms to keep bacteria out but i am assuming it is slight.
2nd question : inline fans have more power when they pull air not push it. as they do not have a lung or balloon that they can fill before they throw out the air and they must have a minimum of 1 metre of ducting before them to push it properly ( unlike you, you will have more power blowing out air than you will sucking it in try blowing out a candle from 2 feet away, now try sucking it out) they usually only push it if you need easy access to the fan or you need to hide the noise of the fan.
if the ducting is totally 100% airtight and pretty straight and the fan is powerful enough you would probably be amazed how far a fan can pull air through a duct. a bit like the draught that would be caused in the channel tunnel by the outside wind if it was not controlled, as the wind travels over the top of the tunnel and then away from and over the tunnel exit, it starts to pull air from underneath through the tunnel, which would suck air in at the other end 22 miles away at an alarming rate... and you must remember that what i have written here is my opinion due to the experiments i have done with fans and cooling. and it is not an exact science. and it does not come from the internet.
there would probably be lots of disagreements with the answer to these two questions. especially from a fat arse, ex public schoolboy, know it all politician, that loves to fill out false expenditure returns to pay for a property empire.
my oh my i hate those f*****s.
