Having problems keeping humidity down

I’m having trouble getting my humidity down to around 45-50%. My dehumidifier I have set to run constantly outside the tent up against one of the tent vents. My humidity is running around 60% and high of 65%. If I put the dehumidifier in the tent(barely any room) having it set at 55%rh it will pull the humidity down to 35% then when it kicks off back up to 65% as well as taking the heat over 81F. Should I go with a smaller dehumidifier or try the moisture absorbing buckets?
4x4x6.5’ tent
RDWC system 4 five gallon grow bkts
5 gallon reservoir
1/10 hp water chiller
950 gph air pump
2”x4” air stone in each bucket
12” oscillating fan
1200w king plus led 24” from canopy
6” 400 cfm exhaust fan and filter


I run my Dehumidifier inside my room and set it depending upon whether I am in veg (55%) or flower (35%). It does produce a good deal of heat, my A/C unit (also inside the 8X8 room) takes care of that.


how long have u ran the dehu.?
it can take days to get the moisture out of the building materials and room contents.!
mine went from 80% down to 50% in a week, thought the damn thing was never gonna shut off.! LOL
even after a week it took another wk or 2 for the unit to run less.

like Merlin said, its better to control the room temp/RH.!
i run my box in a room at 50% RH, using a 70 pint dehu., when lights come on the grow area goes down to 40-44%.
in the winter the extra heat helps, heater runs less,
in the summer my window a/c unit keeps moisture down and the dehu barely runs at all.!!


I only have a 4x4 I’m thinking that dehumidifier I got is to big maybe?

how big is the room that the 4x4 is in.?

how long did u run the dehu in the room.?
a day, a week, a month.?

i think it may be too small,
what size is it.?
what brand is it.?

It’s a GE

It’s in a room about 14x14 I had the dehumidifier in there for the past 2 weeks outside the tent up against one of the vents and still in the 60’s rh. I just put it in the tent and I’m down greatly but fluctuating upto 62% still and temps over 80. I believe I read on ILGM site indoor temps could go as high as 86F is that correct?

I feel like you need a two-stage type of solution to do this in a grow tent or enclosure that’s in another room… the big humidifier or dehumidifier in the room that contains the tent, and then a smaller device inside the tent. Humidity is relative, so it makes sense that by putting your humidifier inside the tent and raising the temperature you will see the relative humidity go down (assuming the exact same amount of water content in the air). Since they are related, you need to work towards establishing the outside parameters for both temperature and humidity for both lights on and lights off.

Temperature isn’t relative, so I usually dial that in first… I look at temps with the lights on with no heater, lights on with a heater, lights off with a heater, and lights on with a heater. My goal is generally to keep everything around 75F with the lights on and 65F with the lights off (ideally). I usually take two days with no plants in the tent to configure my environmental appliances to get them where I want.

Then I tackle humidity. I measure humidity under the above circumstances so I have a baseline to work with. In the winter, that might look like this (again with no plants… having big plants and grow media in your tent seems to raise humidity too):

Room where the tent lives: Average temp 58F and average RH 55% (maintained with humidifier)

  • Lights On, No Heater - 75F, 40% RH
  • Lights Off, No Heater - 58F, 55% RH
  • Lights On, Heater On - 85F, 30% RH
  • Lights Off, Heater On - 70F, 50% RH

Once I have that figured out, I use a small humidifier or dehumidifier in the tent to try and get the RH dialed in. Now, none of this is even possible without having exhaust and intake fans that you can adjust in some manner - either with a thermostat that will control the fan speed like the Infinity fans provide, or by using timers to cycle the fans on and off (which is what I do).

So the first thing I do once I have my baseline is I test different fan cycles. I start with the minimum required using @Niala’s well constructed post here:

How to calculate the exhaust fan cfm with carbon filter and take in consideration HID lights, temperature and humility, a beginner guide 👍

I then run the same tests to get my baselines with fans running at different cycles (right now, as we speak, my fans are running with one minute on, 7 minutes off in a continuous cycle). I had to figure all this out by testing it and dialing it in - if you have Infinity fans with controllers, you can just set the temp you want to maintain and it will adjust accordingly. They are on my list of things to purchase. :smiley:

Now, as I said earlier, in my (limited) experience, plant material counts. Plants are transpiring, they are breathing, etc… as a result, when I get to bigger plants in full flower, I usually end up taking out whatever humidifier I’ve used in the tent and increasing the “on” portion of my fan cycle to reduce RH where I want it for flower (< 45%) .

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Explains things greatly I understand what steps I need to take tocorrect my problem now. Thanks for taking the time to explain all that to me!


This is what I just recently had to do. :sunglasses:

Helped me out tremendously! Keeps my tent at night around low 40’s. Your plants look good! :+1: Good Luck!