How to Control Humidity?

Hello everybody im about to flip to 12/12 and I know that my humidity needs to lower than is it right now I’m at 65% RH lights out, and lights on 55% RH. I’m in a 2x4 tent I have a 6” inline fan and 6” exhaust fan Both CLOUDLINE (1 is the S6 other T6) and 2 6” hanging fans to keep air moving. Would I have to get a dehumidifier or would I be able to adjust my fans to lower RH? Anybody ?

I get in the mid 60s at lights out. I bought a dehumidifier for inside the tent, didn’t do much, I returned it.

One thing I did was put my intake hose in between my girls, and have a 6" fan blowing that air up and through the girls.

Am ending week 5 of flower, and not having issues.


I have my intake hose similar to that will post picture when lights on, okay so I don’t run my intake fan when lights off obviously going to change here on Sunday but say I put my intake fan on 4 and my exhaust on 6 the negative pressure isn’t the best. I have both vents closed (I guess that’s what you call them) if I take The flap off one vent would that help with negative pressure and also maybe humidity?

What is the rh of the source air?

Right now 58% inside room of tent, in the tent right now is 65%

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If you’re drawing air from a 58% source, you won’t be able to bring it below that in the tent. No matter how many fans you use.
Adding a dehumidifier to your “lung” room will drop that humidity, and you can use a controller to keep your tent steady. There will still probably be spikes at lights out, but as long as dew is not condensing on the buds you should be fine.

On a side note, there are several theories on flowering rh. One pushes very low (35-45rh) the other encourages very high (75%)


Okay so I don’t want the little ones that go in the tent I’d need a bigger one do you recommend any ?

Really 75% ? Woah either way I’d have to get some kind of humidifier lol

I’m not recommending high humidity for flowering (yet). I’m still testing it. So far so good. No wpm, no bud rot.

What size is your “lung” room? You’d need to buy an appropriately sized one.
This is what I have running in my basement.

I’ve had it for 18 months. Zero issues.

One can buy cheaper, or smaller, and without the automatic pump, but I like set it and forget it.

They are not cheap to run.

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Let me know how it goes !!
I’m in a 16x16 I’m pretty sure

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You could easily get away with 20-30pint sized. 15 maybe.

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That’s not to bad !and since it’s in my “lung” room with air conditioning also have a portable air conditioner that runs on 70 i wouldn’t have a temp problem would I? Yeah the 30 pint is about 150$ cheaper than what I was looking at

@zee what is your humidity lights on

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Upper 30s to middle 40s.

I brought up the air circulation as it counters any mold build up. I actually plan to add a 2nd fan under the girls in my next flowering, it looks to me the help with bud development…

I almost bought a big room dehumidifier for a few hundred, but kept telling myself, I don’t have a problem to fix.

The 4 months I’ve been on this site, it’s rare to see indoor bud root, when I have it’s been in an environment of 70 to 80 RH…

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My intake is like this but I have it aiming up a tad I have the trellis netting underneath it

Should I keep it or do you think it would work better how yours is, regardless I believe I’m going to need a humidifier lol

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I would still move it to center, if you can. The center of the tent gives balanced air flow, again just my opinion.

Your lung room is air conditioned?
Keep the door closed, drop the ac temp a bit (say 68f) and see if it improves your tent rh. If it works it’ll be cheaper than using a dehumidifier.

Typically the intake vent Is used on the bottom, opposite side from the exhaust vent. The exhaust vent is on top.
I can’t imagineers that 2 properly set up cloudline 6” fans wouldn’t keep that tent at almost the same level as the lung room.

Okay explain lung room, so my tent is in my closet but I keep closet door opened my central ac is set to 70 and so is my portable ac unit, I have the intake at the bottom left same side as exhaust(so I should move carbon filter to opposite side)

Lung room is typically the closed room in which you have your tent. I grow in the basement, so I’ve got a fairly large room to condition. If you keep your lung room air at a decent rh and temp it makes it easier to control your tent rh and temp.

I use digital controllers to turn things on and off to try and keep a stable environment.

Yes. Your intake should opposite and diagonal to the exhaust. Intake bottom, exhaust top.

Here is a VPD chart I try to follow. Had to shrink it to fit in snip

The take away is the higher the temp the higher the RH can be. Obviously within reason. My temps may vary 72 - 82 lights off / on. I have a dehumidifier in the enclosed room that contains my tent (lung room in a sense). I will set the dehumidifier to a lower RH when lights are off.
I should figure out how to use the controller that is sitting in its unopened box.

How does this look