High Humidity in my 2x4

Soo, my girls have started to flower this week. I have been unable to get my humidity down. 3 fans running in tent. 205cfm 4" exhaust fan and 12" carbon filter. Dehumidifier running in lung room, RH 45%. I have another 4in fan and filter. Setup another exhaust? Set it up on intake? Other options?

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45% isn’t all that bad, but would ideally be a bit lower later in flowering.

I tried a 4" fan in a 2x4 when I had one. It wasn’t powerful enough to pull negative pressure in the tent. I put a 6" fan in and it helped a lot.

Plants will naturally put out humidity as a part of the growing process. Probably just need to increase airflow to manage it.


Can you take photos of the plants as well as the ducting?

I have two 2x4s one has a 4" I-power (old metal one) the other one had a 4" vivosun until today I’m putting a ac infinity 4" in it. The I-power is great other then it’s a little loud, I’m hoping the ac will work as good as the I does without the noise I have a 6"ac in my 4x4 and it’s perfect the 2x4s are run as passive intake but I have two racial 6" ac for intake on the 4x4.

Anyway my point is not all fans are created equal the vivosun says it’s cfm is comparable to the I-power but I would say it only moves about half the cfm. As Midwest said it is important to get negative pressure (tent sucked in) it makes controlling the temp n rh easier and keeps the stink going through the filter instead of escaping through other openings

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It’s more work but could you stagger the watering so you’re only doing half the plants and alternate?

Lung room is 45% tent is averaging 63%

More airflow into and out of your tent will probably help the situation then.

Sorry pic of plants is from Tuesday, they are a little bigger now

Is this your output? Output should come from near the top of the tent. Air near the top of the tent will be hotter and therefore carry more moisture. I would suggest that your input be from the bottom of the tent and your output be from the top of the tent.

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Intake, both sides are like this

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You can lower your humidity by lightly defoliating your plants. This is one of the few reasons I’ll defoliate. Your humidity is high in the tent, at least where you’re taking measurements. Removing a few lower fan leaves will reduce transpiration. Again, go slow. If you don’t see a decrease in humidity, something else is at play.

Edit: what’s the blue material on your intake?

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Is the pre filer material that you would use on furnace filters

Ac infinity raxial fans are just as cheap as the vivosum ipower 4 inch fans and the raxials run alot better quieter. I have a 6 inch raxial on my 2x4 its 6 inch with 4 inch flex tubing thru the ports works well so far sucks tge tent in at third power tge raxials also come with a speed control knob. Check them out way better than the 4 inch stuff i havnt tried the 4 inch raxials but the 6 is sweet


I have a spare 4" ipower. Would it be more beneficial to put it on one of my intake ports or run a 2nd exhaust (have another 4" carbon filter as well) @Mark0427 @KeystoneCops @MidwestGuy
Edit: I do have negative pressure now


@Mark0427 I have two 6" rexial fans on my 4x4 one on each side as intake fans they’re great the two keep up with the 6" cloudline i set the speeds to where the tent is sucked in but not to the point it looks like it’s gonna implode lol. That’s why I put the two rexial fans on it, I don’t use the big vents on the bottom (light leaks) of the tent just 6" duct like @CooterJuice has in his picture I was afraid my tent would collapse when I ran it just passive intake. I was warned by ac infinity that the rexial fans were not designed for any type of restrictions and that even to many bends in your duct work would shorten the life of the fan, they said that they wouldn’t recommend using the rexial fans on a grow tent at all. I figure as an intake they’re fine the tent has negative pressure so they don’t have any restriction at all

Edit = as for the price I think I gave like $30 a piece for the rexial fans


So I cleaned up under their skirts a little and repositioned my one intake duct closer to dehumidifier. It’s gonna get more crowded for sure. I think they look good though

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Instead of adding a second id just get a bigger one for exhaust unless income is an issue. U might be able to take the 2 4 inch and get a coupler to like a 6 run the 4 inch as little as possible tapped into 6 and out all 6 inch. Can just tape everything real well at a y area with tape make your own y from the 2 4 inch to 1 6 inch kinda oval the end of the 6 that the 2 4 inch will connect to prolly easier to just get a 6 inch raxials work great without alot of restrictions. I dont care about smell so i dont have a filter hooked up to mine and its kick azz for a 2x4

Yea u been looking at the AC infinity 6". Give me a good reason to buy it, lol. I thought the 6" and 24" filter in my closet grow (30"x60"x90 was overkill until they hit flower,lol. I have to run a filter for my location sadly

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Wait and see how the defoliation affects your humidity. You can still take a little more off.

Keep in mind, the more you remove, the more nutrients your plants will need to replace. It’s quite common to see deficiencies pop up after a defoliation.

Like I said before, go slow and assess.

Thanks man it has helped it some for sure!!! Tomorrow is feed day so I’ll maybe thin out the top of the canopy a little in a couple days? And after looking at pics, since I’m in fabric pots, should I roll the top of pots down?