# Humidity Control Help



## idreamofgreenie (Feb 23, 2021)

Hi y’all. For some reason my basement grow room is really dry. I am running two humidifiers to keep it around 60% for my seedlings. But I just installed an air intake fan and an exhaust fan and now with both humidifiers running the humidity is stuck at 35% … the exhaust fan is just sucking it all out. How can I circulate my air AND keep the humidity? I am using a King LED 1000W in my 3x3x6 space. Also a small space heater since my basement is cold.


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## ROSTERMAN (Feb 23, 2021)

What air are you using to exchange the grow room?
Is it fresh air from outside, or just from the basement area around the grow space?
Outside air has very low humidity this time of year. Use the basements air there are enough air leaks to exchange the gases you require.

*Air* in your *grow* area *should* be *exchanged* at least every 5 minutes. If you are using a *grow tent* that is 5' x 5' x 6' this is 150 sq/ft of *air*. For optimal airflow, you need a filter and fan that can move between 30 and 60 cubic feet per minute (CFM).


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## ROSTERMAN (Feb 23, 2021)

I would also make sure you have a good working calibrated humidity meter  just in case your is off. (lots of the China garbage is just that )


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## idreamofgreenie (Feb 23, 2021)

Hey folks, thanks for the help! I am using the basement air for intake, not from outside. I did buy a new humidity meter and it is registering a higher level than the cheapo one I had. 

My fans are 6" inline fans with 240 CFM. They are causing a small gust inside. Plants are trembling. Is that okay?


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## Vegas Kid (Feb 24, 2021)

The Mojave desert is one of the driest places on earth and a lot of us grow here with the ambient humidity of 15 to 25%. While it is troublesome now, it will be a blessing when you put the plants in flower. No PM or mold. I grow in a 4 X 4 with 600W HPS.


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## bigsur51 (Feb 24, 2021)

like the Vegas Kid , it is really dry out here on the high plains

but I have found over the last 12 years of growing both indoors and outdoors , I will take low humidity over high humidity any day!

count your blessings and get rid of those two dehumidifiers , your plants will be fine and will grow good in 5-10% humidity from seedlings to harvest


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## pute (Feb 24, 2021)

The only time I really watch my humidity is in the spring.  Sometimes it gets so wet my humidity gets north of 60%.  Time to crank up the fans and watch for PM.


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## Bubba (Feb 24, 2021)

Vegas Kid said:


> The Mojave desert is one of the driest places on earth and a lot of us grow here with the ambient humidity of 15 to 25%. While it is troublesome now, it will be a blessing when you put the plants in flower. No PM or mold. I grow in a 4 X 4 with 600W HPS.


Same here, 4 x 4 and 600 Watt hps. Heat keeps humidity low for me...usually 38 to 42 or so.

Really want to switch to two of the Mars Hydro SP 3000 for the 4 x 4.

Bubba


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## zem (Feb 24, 2021)

Where I live it rarely goes as low as 35%. Raising the humidity is not a problem, while lowering it is a problem. You could hang towels like curtains all around and wet them, wet the walls, floors and surfaces.


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## pute (Feb 24, 2021)

zem said:


> Where I live it rarely goes as low as 35%. Raising the humidity is not a problem, while lowering it is a problem. You could hang towels like curtains all around and wet them, wet the walls, floors and surfaces.


I put a pan of water with a fan and a wash rag draped over the side in the room.


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## BoCoGrow (Feb 24, 2021)

You mentioned growing in a 3x3x6 space, is that a grow tent in your basement?  If so, you don't really need both an intake fan and an exhaust fan; when the exhaust fan runs, it will naturally pull fresh air in through the vents at the bottom of the tent.

I was recently struggling with humidity issues myself.  I've made two changes to my setup that have helped tremendously.  First, I bought a humidifier with a humidistat such that I set the desired humidity level and the humidifier will continue running if the humidity level is below target.  The humidifier is inside my 4x4 tent.  Second, I installed a controller to my tent exhaust fan such that I can set min/max temp and humidity and the fan won't turn on unless the environment is out of range.  I have a 10" oscillating fan inside my tent for circulation.

My grow tent is in a larger dedicated 10x10 room, and that room has an additional exhaust fan that runs for 15 minutes every two hours to exchange the air.  I grew years ago but I'm still working to dial in my new setup and relearn everything I've forgotten over time, but things are starting to come together.  Good luck!


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## idreamofgreenie (Feb 25, 2021)

All, thank you so much for the feedback. What I'm taking away from this is that lower humidity than optimal is okay and my plants can still grow anyway. Also that fans and humidifiers with smartstats may be a good investment down the road.

To BocoGrow, it's not a tent, it's a tall storage space under my basement stairs. I drilled two 6" holes at the top and bottom for the exhaust and intake. So maybe I take out the intake fan and just let the exhaust pull the air into the room? I heard negative pressure can be good for the environment... but it's still going to pull the humidity out of the room.


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## Bubba (Feb 26, 2021)

Yes, negative pressure is good...all the yummy smells don't escape, except through the exhaust. I have a carbon filter on that end eliminating smell.

I use a fan pulling the exhaust outside the tent and then into the filter, also outside tent. This right now is giving 38% RH at mid to high 70s F temp. Temps top out 79-80 F.

Bubba


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## WeedHopper (Feb 26, 2021)

Negative pressure is awesome. It means the air transfer is spot on.


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