Newbie with Negative Pressure Question

Just finishing off flower room and noticed as soon as the door shuts air builds behind my panda film. Not coming off the walls but it is ballooning. Is that a good amount of negative pressure or too much? I have an 11x11x7 with an 6" can fan and filter (stepped up to 8") cooling two 8" 600w mh (Sunpulse) along with a 6" intake fan. When I open the door, there is some pressure against it. Also, since this is attached to my veg room (seperated opening with panda film) some of that trapped air is moving to my veg area...good, bad?? Thanks!

If it's ballooning you have positive air pressure because there's too much air and it's blowing the walls outward. The room is pretty big so I would say having an intake fan isn't horrible, but if your exhaust fan is big enough it can create negative pressure on it's own.

I recommend just stepping down your intake and making sure it's A) as close to the floor as possible and B) as far from your exhaust fan as possible.

How many CFM is your exhaust/intake?

Your room is 11x11x7 or 847 cubic feet so an 850 CFM fan would probably exchange the air a little less than once a minute since once you attach the filter you'll lose a bit of suction on the exhaust. In smaller operations, the negative pressure is created by not using an intake fan and the exiting air automatically equalizes by sucking more air in.

It sounds like your intake is too big imo.

EDIT: By stepping down your intake, either create a smaller intake hole, step it down with some conversions to 4", or use a smaller fan (or get a speed controller to make it run at a lower speed) -- preferrably a smaller hole or a smaller fan.

very hard question to answer, with out more info if your not co2 ing , then you need a lot of ventulatin fresh air on the plants so they can get the co2 they need from a lot of air passing on them by fans , if you are co2 ing besure to air the room out let the co2 out at night , to normal level , air pressure will not hurt them unless your talking ear popping crazy.

if your not co2ing ide poke a few holes in the wall let it breath a bit more let the fan work a bit less youll need a lot more air flow fresh air = bigger yields of those chilly peppers. lol with a kick

Agree positive pressure , your fans are proberly in the 300-450 cfm range , good for you using 8 inch (proper size), you have 2 choices here ,but dont step down the size of the duct work it will work, but you will be stuck with what it is, I recommend using a damper before your intake fan this way it will give you ability to control your eviorment better ,by giving you a adjustment factor ,this would be beneficial also on controlling temps , if you really want o controll it you can set up a barametric damper on the exhaust fan also. this will enable you much more control .

Thanks for the input. I'm not running CO2 and the intake is at waist level, guess that was one mistake. I could cut in a passive intake close to the floor and maybe that would solve if I'm understanding correctly or would a speed control on the intake fan work as well? Thanks again!!

I discovered it balloons even with my fan off so I will try a smaller intake and lower to the ground..

I must speak dutch, Jeeez , Look your room is in positive pressure correct, So if you cut a hole for passive intake ,what do you think that will do, think of this, rite now your room is a balloon OK , well lets blow the balloon up ,now lets add what you call passive intake, Put small hole in the balloon ,WTF do think will happen ,do you really think air will go in the hole in the balloon. You have 2 choices buy a $8 damper put it on your supply fan and control the amount of air entering the tent , or take that fan out of the equation and then cut your passive hole in the room.

B&Bgrowers said:

Just finishing off flower room and noticed as soon as the door shuts air builds behind my panda film. Not coming off the walls but it is ballooning. Is that a good amount of negative pressure or too much? I have an 11x11x7 with an 6" can fan and filter (stepped up to 8") cooling two 8" 600w mh (Sunpulse) along with a 6" intake fan. When I open the door, there is some pressure against it. Also, since this is attached to my veg room (seperated opening with panda film) some of that trapped air is moving to my veg area...good, bad?? Thanks!

Click to expand...

First off 1200 watts in a 11x11x7 room is NOT ENOUGH. At around 150,000 lumens with two 600 watt MH lamps that's only 1,200 lumens per square foot, not even half of what you need. You need two more 600 watts for a total of four in that size of room, or 3-4 1,000 watts, if you expect to get decent yields.

As for your pressure you have too much positive pressure, which is too much intake and not enough exhaust. You want negative pressure for odor control, more exhaust then intake. Get some fan speed controllers and dial it in.