Ok, i have been on a teter toter about this situation… I have friends who grow photos indoors that say i need to vent the tent to keep it from creating negative pressure, and to keep airflow open… So, up till now, because im in 3rd week veg and have turned light intensity to 60%, i have followed another friend’s advice who also grows indoors except only autos to make sure i have negative pressure on tent… which now i have… photos to follow, first will be tent open on the bottom as you can see light. Next will be tent with negative pressure … the VPD is what im shooting for anyways… has not made any difference except had to turn inline fan up…is my plants getting enough water? Third photo… any advise is always welcomed… btw first-time autos…also i do have airflow running into tent. Fourth photo.
Sorry guess photos didn’t come out the way i wanted…
Neg pressure is mainlly for the smell to stay in the tent.
I never run a vent. I just don’t need to at this point. 3 years growing and no problems.
To control smell a filter and some negative pressure is what is needed.
Or if high temps are an issue,
But for plants your size the vent is unnecessary right now.
Nice set up btw
Photos or autos - it makes no difference other than photos need around 12 hours of darkness.
All negative pressure means is air is being pulled from the tent at a higher rate than air is entering it. When plants are small and have no odor negative pressure isn’t necessary. The exception may be for climate control - that is drawing conditioned air into the tent to moderate temps or decrease humidity. This can also be achieved by opening the tent. I do it all the time. It just depends on circumstances and there is no rule dictating what to do.
Photos and open vents - the vents will need to be light proofed. If you have an unused port, stick a piece of 6" duct in it and bend the duct 90 degrees.
Thank you… it cost me… running right at about $1500 so far
Ok , thats good to know about the light and darkness to vent… never thought of that…
I am running 18/6 throughout growth.
I didn’t think i needed to vent if i had an air source coming in???
@Lost4Sure Howdy!! These are all upfront costs lol!! You’ll soon have everything you need and your subsequent grows won’t require much more than your love and some time! Wait’ll you start reaping the Bounty of BUD!!
As your discussion is about “venting” I have a question for debating.
Air filtration, inside tent or outside? Manufacturer says either can be utilized.
I was contemplating the next (needed?) change and came up undecided, with a bias for outside to attic.
My design attached
Manufacturers show
and
controlled by the Infinity Bluetooth
@beardless Opinion?
Hopefully someone will assist in the sizing of components.
I don’t think the attic exhaust will function as intended. The fan will just blow the exhaust air through the center of the filter. Unless the filter is some type of box filter. If this is the case, I think the fan would need to be on the extraction side rather than intake side.
I have an external filter on a tent and push the air through the charcoal membrane. It isn’t the prettiest contraption but it works. In this application the prefilter is rolled and put inside the filter.
In my closet I have a traditional setup.
The closet has two exhaust exit points. One returns air to the room where the closet is located. I use this port during the cold & dry months. When it warms up and humidity increases I exhaust into the attic.
It is set up to return air into the room.
I also use a filter and fan to scrub the air going back into the closet.
This is really up for debate. Putting it outside of the tent will give you more head space. Leaving it in will give you less noise.
On your diagram you have 2 T6s fans. You’d have a 6 inch on the top and a 4 on the bottom. Direct recommendation from the manufacturer.
@DEEPDIVERDAVE
All, I appreciate the air filtration discussion. Already up to revision 5. Fortunately, planning stage with items on purchase, awaiting shipping or delivery. From reading manufacturer (wanted the intake 6-inch fan split into two tents) and comparing filter design (box/no box), I can put the filter inside the flower tent with 6" exhausting fan outside. Two 6" tent to tent connections. Intake may need modification so both tents get the 6-inch intake fan circulation air. Additionally, a window exhaust fan is the first, easiest, and cheapest modification.
Getting better with a little help from ILGM friends. Thanks
Sucking air through the exhaust filter is more efficient. For me, even though my tent is 7’, I am glad I have the extra foot the fan and filter would have used.
Good luck with the project.
Whoaaa. That’s a lot of filters there, maybe you won’t smell anything 
I’ve never used more than one and can always smell my grow, but I prefer it…
I love the smell. My wife does not. Imagine that. A real buzz kill.
I like the smell but my neighbors dont…
There is really no reason to invest in a HLPA filter on your intake if your tent is in negative pressure. Since the tent has so many tiny openings via the zipper, stitching, and wiring penetrations. A screen or cheaper filter will do.
If you plan on running flex duct longer than 5 - 7 foot lengths. You really need to step up to 6 inch duct. It is OK to stay with the 4 inch fan, but that flex duct really resists air flow, ( it is all the little ribs on the sides, they form little eddies as the air moves over them). I changed my duct and tent flanges to 6 inch, using the insulated flex duct. What a difference, I now have 3 times the air flow.
I find it best to use both a intake fan and exhaust fan on speed controllers, and set the tent pressure at slightly negative using the speed controls. This handy as you can increase or decrease air flow as needed while maintaining the same tent pressure. Also less noise.
I have played around with tent pressure during flowering, and think there maybe a slight benefit to this. But I also don’t think a slight negative or positive pressure will effect your plant, but they don’t seem to like extremely negative pressure IMO.
If I can help let me know, I had 45 years in the HVAC field.
Here is a cheap way to move your filter and fan out of your tent, and maintain the correct air flow direction through the pre filter. You will need a 5gal bucket with lid, a couple flanges, short piece of smoke pipe, and some sealant. All all this fit together like a glove.
6" intake fan split for both tents. Additionally, both tents have cross-over 6"ducting times two.
6" filter diameter that is about 15 inches long (ViVosun 4x4x6.5 kit).
Exhausting filter inside flower tent and sucking into 6"ducting into 6-inch fan (both fans on controller).
Window exhausting available, first, cheapest, and easiest. Almost ready to flip into flower.