Heat and Humidity control for a newbie

Total newbie here. Trying to get the humidity under control.

I’m doing an indoor grow 2x2x4 grow tent. AK47 autoflower from ILGM.
Home made autoflower soil in 3 gallon fabric pot. 300w UFO LED light and 150w blurple LED. Just started using Advanced Nutrients Micro, Grow, Bloom today. 17 days above ground.

I’m actually sort of doing an indoor/outdoor grow when it comes to temperature and humidity. Let me clarify. I’m in my uninsulated shed. By the time I received all my stuff the temperatures were scorching here. Temps in the shed were hittin 117 degrees just as my seedling popped above the soil. So I put a portable AC unit in the shed, which lowered the temps 10 to 15 degrees. Still too hot. I built a super small room (5x6x4 feet ish) out of foam insulation panels, corners taped. I put the AC inside the mini room with the tent, in an effort to cool off just the little room, rather than the whole shed. This didn’t work at all because the room is so small that it created a vacuum and the AC couldn’t breath, so it wasn’t cooling at all. So I moved the AC outside the little room and built a contraption to vent the cold air directly into the mini room. This worked great. Temps are 70-80 in the day and 60-70 at night inside the mini room. I have since run the duct from the AC directly into the tent and have a temperature controller on order to turn the AC on and off to help maintain temps even better and save electricity.

My problem now is the humidity. I was thinking the AC would help lower it, but it doesn’t seem to be helping at all. RH has been in the 70-80% range for a while in the tent, higher after a rain. RH never drops below 65% here, all year long. Even with the exhaust fan running humidity is still 75-80%. The only time it gets low (45%) is at night with no AC, I turn it off at night because it gets too cold, but the temps In the tent are at 90 degrees.

I guess my point with all this rambling is about dehumidifiers. The portable AC has a dehumidifier on it, but I can’t run it inside the mini room because of the vacuum. I would like to get a small dehumidifier to put in the tent, but I don’t know how well that is going to work if the AC is pumping humid air into to. For that matter, the extractor fan is sucking humid air into the tent too. Like I said, I’m only 17 days above ground, so I have time to work on it, I just know I need to get it under control before flower. The last thing I want is bud rot.

Has anyone had a similar situation and did a dehumidifier help? Do you think it would help in my situation?

Also, I’d like to mention that I switched over to the blurple light because the 300w white light was hot inside my little tent. Little “Bud” seems to like it.

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Your AC does not put humid air out.
I would consider putting a dehumidifier outside the make-shift grow room.
Run a second hose into the grow space with one end connected to the output on the dehumidifier kinda like this, if you can.

This way it exhaust the dehumidified air into the grow space. I use a remote thermometer to monitor the climate inside my grow space. You may have to play with settings and distance from the wall, but at least it may help. It did for me.
Good luck! :+1:t2::sunglasses:


Thanks for the info and photo. I may have to try that. This thing is turning into an environmental control experiment. Haha. I’m gonna have hoses running all over the place.


I agree with putting a dehumidifier outside the grow area. My tent is in my basement and where I live through almost all of spring and summer it’s very humid. I have one outside my tent and it helps a lot. My humidity now is sticking around 45 to 55. An in-line fan and small desk fan inside of tent also helped me with humidity and heat problems. Hope this helps!

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Never occurred to me to put my passive intake over the dehumidifier. You just solved a lot of issues for me :v:


I have a 5’ x 10’ room with two 6” intlets and two 6” outputs.
I’ve got 6” exhaust fan on one outlet and a 4” exhaust fan on the other outlet.
When I put the humidifier near one of the openings, I can control the temp and humidity in my room so much easier.
My grow room pulls from another room wihich is usually around 77F. Rh fluctuates quite a bit but this summer haze been brutal.
Grow room stays pretty steady at 82
/50% lights on and since I’m in hydro and the water temp is 68F when lights are out, temp can get down to 74F Rh 50%
I have to monitor and adjust occasionally but at least I can keep it under control most of the time.
Even when I had a tent, I had to run it that way and it help a lot. It was a little more of a challenge with the tent then with my grow room.
Glad it helps! :+1:t2::sunglasses:

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My humidity gets out of control at lights out even with fans full blast . I dehumidify a lung room which helps but adding a second dehumidifier and placing the intake right on the intake should do the trick :+1:


I was doing some thinking based on the suggested idea of directing the dry air from the dehumidifier into the tent. Since my portable AC has a DRY setting, which is a dehumidifier, I thought I’d try it out before I spend $50-$100 on a dehumidifier. My test yesterday is represented in the photo here. The weird part is that I placed my hygrometer inside the duct from the AC and it showed 65% coming out of the duct. That doesn’t seem like dry air to me.! Again, I don’t see how a dehumidifier will help if AC is blowing humid air in.