RH% and Temperature Issues

Hi all,

I hope everyone is doing very well. I am begging for help please…

I have enough equipment for 2 different tent setups and I have tried both but have the same issues:

Tent setup #1: 4x4x6.5

2000W COB LED light
8 inch vivosun fan w/ speed controller for exhaust (inside tent)
8 inch carbon filter
Humidifier (inside tent)
8 inch vivosun fan w/speed controller for intake (outside tent)
Oscillating fan

Tent setup #2: 4x4x6.5

2000W COB LED light
4 inch vivosun fan w/speed controller for exhaust (outside tent)
Oscillating fan
Passive intake

In both setups I cannot get the temperature up past 23°C and no more than 45% RH??? I have literally tried everything I can but nothing seems to work. The only time I can get the temps and RH up is when I turn off my entire ventilation system and simply keep the oscillating fan on…

I should mention I am but only 4 days in so for seedlings I need to get it to 25°C and 75%RH…

Please some help as I am at a loss!!!

Thank you very much in advance for any help on this!


First thing i would do is turn off the supply fan. Start the exhaust at 50%. Wait an hour. If its stable then start making slight speed adjustments to both until your where you want to get to. Once your good on the exhaust, adjust your supply till you are slightly negative on tent pressure. I might take awhile but with 8" fans you are ptobably moving waaaaay more air than needed with a 4x4.



Once your plants mature some they will drive humidity up significantly. The numbers you got arent ideal for seedlings but ive grown way colder and dryer. Its not a disaster till shit stars dying rite😂

My RH% is always in the low 40s, since I started 3 weeks ago, my girls are happy and healthy.

1 Like

This would be the 3rd time I attempted this process but I will give it a go.

Also, how about my 2and setup…4x4x6.5 tent with only a 4" exhaust with carbon filter…intake is passive…still the same issue…

@CanadianTrooper @Hellraiser, gave you solid advice on lights, I will share advice he gave me. If what you have been doing isn’t working, don’t do the same thing. You must try something else.

He has a grow journal that many follow, I do, and as a first time grower, very happy with my results. Don’t jump the gun on the same process if it hasn’t worked. I can post the link to his grow guide if you like?

1 Like

To warm up the tent, you can do a few things, add more light which brings more heat. Slow down the exhaust as much as possible, if still too cold, use a timer run fan 15 on, then off 15 minute off, then on, if that don’t work try 15 on 30 off, you’ll find a timing that works. Don’t worry about humidity, the necessity of high humidity is often overblown, I do whole grows at 30RH or less, no problems.


Timing was the next thing i was gonna tell him. A 4.00 timer on the exhaust and supply. You dont want the tent positive tho. Youll need to make sure the exhausr runs more than the supply

1 Like

Adjust temp of room tent is in as well as rh.


Is it okay if the mist from the ultrasonic humidifier touches plant?

Also, if it is okay, I have figured out how to fix it now. You made me think with the comment that 8" exhaust and intake is too much air moving in and out for a 4x4 tent…so I pulled everything and simply setup the 4" inline with carbon filter as the exhaust inside the tent…good news is that its fixing temperature and RH%…bad news is that I am now sitting with $600 worth of fans on the sidelines…what an absolute waste…perhaps they may come in handy when the girls grow especially with foliage…perhaps then the RH% will be too high and I will have to use the 8" exhaust setup…just later on in the grow? Thoughts on this…?

1 Like

Always good to have backup equipment and you might change stuff around as you evolve, hell with those low temps I’d be tempted to pick up a 1000 watt air-cooled HPS and you can use that 8" fan again as that’ll give you some heat and some serious light, a lot more light than you’re getting from that 2000 watt cob that’s probably more like 400 real watts.

The mist is fine if you’re using RO or distilled water, with tap, it’s gonna leave a lot of calcium deposits (white dust).