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Humidity/Dehumidifier Problem!


New Member
Hello Everybody!
I am in 4th week of flowering and my humidity wont go under 55-60% RH. And this is when ALL the doors/opening in my grow tent are open and when the 2 exhaust fans is at MAX. One of the exhaust fans exhausts 820m3/hour and the other 420m3/hour. My grow tent size is 2,4x2,4 meters.

I have tried everything to get the humidity down. I first bought a dehumifier that has an airflow of 100m3/hour that costed about 150 euros. I thought this would help. But it didnt help att all! I tried to put it in the center of the tent, nothing changed, i tried to put it outside the tent nothing changed either. I tried everything that i have found on the net for example i builded a box outside the tent and then put the dehumidifier there and then i used a active intake fan to blow the air in to the tent. Nothing happens. The. I thought maybe its the dehumidifier that is not strong enough. So yesterday i bought a dehumidifier for 500 euros that has an airflow of 520m3/hour! 5 times more and the best you can buy in that size on the market.

And i tried everything that i tried with my first one. Put it in the center, outside but nothing. By the whay the RH outside the tent is 48-50%.

Then i thought that maybe my exhaust fans is too strong and that the dehumidified air is beeing exhausted too fast, so i reduced the exhaust fans below 520m3/ hour and put the dehumidifier to blow 520m3. The RH raised to 70%!!

The lowest RH i can get is 55-60% and this is when i open every opening in the tent, put all exhaust fans at maximum speed and open every window in the house so it blows storm inside.

The dehumidifier doesnt do a change at all.

Please can somebody with experience of using dehumidifiers in grow tent help me!
This is the first time i run on a problem like this and i dont know what to do!

I dont want to have the tent wide open all the time, the smell is all over the aparment.

Happy for an answer.

Thans in advance


New Member

This is a picture a found on the net that they claimed would work... Ive tried it but nothing happened.


Well-Known Member
If the RH is higher inside the tent than outside, Maybe you have too much water in the tent. Are you growing in soil or hydro? If soil, are you over watering? remove excess water runoff from trays. You can also try running an A/C unit in the room where the tent is, This should help bring down RH. A small fan blowing over the tops of the plant may also help.


New Member
I am growing in Coco and im using autopot watering system. the rh outside the tent is 45-50% and 55-60% inside. I think that the dehumidifier wont help because the plants is producing the humidity( i have a lot of plants on a small space) because my dehu dehumidifies over 15 liters/day and its still around 60%. So i think That more oscillating fans blowing on the plants will be the best solution!
Since i am a newbie grower i started to panic as soon the rh came close to 55-60% but i think as long as its under 60% im okay,,, am i right?


Well-Known Member
you will be fine for now. When in flower you are going to want to keep the RH a little lower. Maybe veg the plant a little longer until the RH begins to fall in your area and you will be ok.

Good luck with your grow!


New Member
I don't vent any air to outside from my grow room. Can you vent just your lights without venting the whole tent? I air condition and dehumidify and carbon filter my air and don't want to loose any of it. I can go into the 30% range easy if i'm not careful. Your new dehumidifier should work great if you stop turning over so much air. Also, water less. More fans won't lower humidity, in fact they'll raise it (faster evaporation from everything). Temp is crucial. Some dehumidifiers won't work below 65 or 70 degrees (like at night). That's usually not a problem in a grow tent. It's usually too high. Use vent-able lights if heat is why you're turning the air over so much, or an air conditioner. Good luck- don't give up!


New Member
I have a dehumidifier. Works perfectly. I am living in a place where humidity remains always high . Generally, humidity climbs from 70% to 95% . After running dehumidifier relative humidity remains 50%, which is much proficient.

Fuzzy Duck

Well-Known Member
Mmm technical stuff ah !

Auto pots work on a gravity based res & the pots sit in a mini res/tray of water with a manual valve which works on water level before topping up mini res/tray... ye i read up about the system in the past !

It could mean that hydroponic systems with lots of water present under lighting may raise RH as their is much more water available to evaporate raising RH via ambient temperature !

You also have different micro climates ! the RH/temp out side of tent & the one inside of the tent at some point this will merge to medium level whilst lights are on... how ever i suspect you RH during lights off is much higher & normally a spike in RH with lights off can be expected !

This also includes RH/temp of the out side world aka out side of the house !

All 3 micro climates are different so to speak...

So it may well depend on the set up vs passive intake, intake from out side of house to where the dehumidifier is to the point of extraction/exhaust ?

I use dehumidifier myself & it is not in side of the grow tent as the side effect of dehumidifiers is that they produce heat & that also they only can treat X volume of air per hour vs extraction fan volume of air taken out, it almost defeats the object when it is inside of the tent ?

So in my opinion a dehumidifier is best used out side off the tent in the room which the tent is used in, as it will treat a greater volume of air via a passive intake of the grow tent over time.
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