Q:positive vs neg. air pressure

Good evening, all. Can anyone explain positive and negative air pressure? I've been reading and reading here and other places trying to figure out why a can fan, 5 months old, would still allow odors to be detectable outside. u We sed an automatic spray air freshener in the room, too. Could that be the reson? We have tried about everything, watch the humidity ( I read somewhere they aren't effective above 50%? We've taped , caulked, plugged any perceivable air leak, and am about to freak. Oh, BTW, the strain is Master Kush from Nirvana. Also, the pre-filter has turned grey-does this mean the prefilter needs replacing, the whole thing needs replacing, or it's just from the occasional medicinal dose administered in the area? Appreciate all the effort and ideas!

neg pressure: air is sucked into the room because there is a slight vacuum in the room relative to the exterior.

pos: air is blown out of the room because of the difference in pressure.

Differences in pressure are created by fans blowing into or out of the room. A fan exhausting air causes neg. pressure. This is what you want, because pos. pressure blows the smelly air out of the room.

If all you had was an intake fan, the fan would create pos. pressure, so you always want a stronger exhaust fan than intake, or no intake fan at all. I usually don't use them.

For smell, replace the filter, if you need more smell control look into in-duct ozone generators. Carbon filters are rated for a certain amount of air movement through them, so make sure your filter matches your fan.

Thanks for the reply. The generator sounds very interesting! I will certainly look into it.

More info needed.

What is the size of your room (W x L x H)?
How many plants?
What is the CFM of the fan?
What is the diameter of the duct?
What is the size of the intake port?
Passive or active intake?
How long is the duct work and how many 90 degree elbows?
Where does the fan exhaust (if interior exhaust, describe)?
What is the size of the can filter?

If you dial these factor in correctly you should not have an issue. A little ONA should take care of any residual odor. If this is a critical factor and you still can't manage to contain the odor then you could consider a tent, although that should not be needed if you get the above factors matched up.