Negative pressure in my grow room.........

How do i control negative pressure in room............. I have 2 8 inch fans blowing room air into thru the lights and have 1 12(in) fan enclosed in a box that intakes the air and exhaust thru a carbon filter.......i have 2 intake vents holes cut into walls (12in x 8in) with (6in tips) with 6in ducting that lays on ground that intake outside air....... Without fans pulling it in...... Now....when i turn fans on the whole room starts to suck in pulling mylar from the walls.....i have 1 side or should i say wall made from mylar stapled and taped from 2 (2x4's ) that go across the top and hangs down.....that encloses the room....... When i put a piece of tissue next to the vents...i dont get any air movement that shows if air is either getting sucked in thru vents, from outside or inside...... I was thinking maybe get 8in ducting and attach it straight to the back of the fans and attach it to the ducting where the intake vents are and have it pull it straight thru........but i though that passive vents would have worked....... Any ideas ........i would appreciate.........also the room is not airtight....is that a problem........

your passive intakes are not effective enough to cancel out the pressure created by your exhausts, i had the same issue , even placing normal fans infront off my passive intakes did not work, i even swapped and tried with passive exhausts and powered intakes , result was i had an inflateable tent in my loft lol, gl tho =D

ps i just saw the photo and i would link the 2 intakes into 1 6" inline fan.

so what did you do to fix your negative pressure problem......? I do have a 6in inline....im going to try it...........any other ideas........?

How many fans do you have running as exhausts?

What size in inches are the fans?

For every exhaust fan with any size fitting 4inch 5inch 6inch etc you should have 2 holes the same size as the fan.

1x6inch fan = 2x6inch passive intakes.

2x5inch fans = 4x5inch passive intakes.


You have to make enough surface area for the fan to pull enough cool air in passively so that your tent does not suck from the pressure.



J

[QUOTE="G"green;5291874]so what did you do to fix your negative pressure problem......? I do have a 6in inline....im going to try it...........any other ideas........?[/QUOTE]

that would do it , use a t-junction and join the 2 intakes to your 6" fan, i did this and had the issue no longer ...keep the fan low down as in your picture and exhaust high up above the lights as you are doing.....