Humidity Challenge

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Hello All! I'm looking for some advice on how to deal with my 4x4 grow tent as I am having issues bringing the humidity down. Here are some details:

Plants: 4 autos in 5 gallon fabric pots using FFOF

Light: 300w LED on 20/4 schedule

Exhaust Fan: Always on at 75% speed

Location: Mid-Atlantic so do have alot of humidity naturally in summer

I'm just going into preflowering and I'm worrying that a humidity around 70% is going to create mold. I've got a tall circulating standing fan and a mini fan hanging from ceiling always on, as well as two 400 Sq foot dehumidifiers, two eva-dry hanging and even a DampRid. I can't seem to get the humidity to drop lower than 65%. I do have two fabric panels open on the tent for circulation purposes and haven't watered in 48 hours.

Any advice you have or more info needed please let know.
 
Have you tried boosting your exhaust fan? I have to keep mine on at 100% during the summer.

And what about the room housing your tent? My tent is in the closet of a bedroom, but I keep a portable AC unit in the bedroom to keep that room as cool and dry as possible. If you can't tackle tent climate, at the very least, try to tackle your ambient environment. I exhaust into a bathroom, so I leave my bathroom's exhaust fan on 24/7, and my bathroom has a HRV exhaust as well that I usually leave on too. I also use a dehumidifier that will move around from the bathroom to the closet, depending on how humid of a day it is.

And do you have room to bump your temps up a few degrees in your tent without risking over-heating your plants? I use a small space heater which is a source of "dry heat", pointed at my tent's intake. That's usually enough to boost the temp in the tent by a couple degrees, and in the process, it reduces humidity in the tent a few points as well. I can't keep the heater in the tent or it would get too hot.

And do you track VPD?
 
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Have you tried boosting your exhaust fan? I have to keep mine on at 100% during the summer.

And what about the room housing your tent? My tent is in the closet of a bedroom, but I keep a portable AC unit in the bedroom to keep that room as cool and dry as possible. If you can't tackle tent climate, at the very least, try to tackle your ambient environment. I exhaust into a bathroom, so I leave my bathroom's exhaust fan on 24/7, and my bathroom has a HRV exhaust as well that I usually leave on too.

And do you have room to bump your temps up a few degrees in your tent without risking over-heating your plants? I use a small space heater which is a source of "dry heat", pointed at my tent's intake. That's usually enough to boost the temp in the tent by a couple degrees, and in the process, it reduces humidity in the tent a few points as well. I can't keep the heater in the tent or it would get too hot.

And do you track VPD?

Thanks, I'll bump up my exhaust to 100%. I hover around 24-25 Celsius in my tent, so based on the VPD charts I've seen 60-65% humidity is spot on. I've just heard during flowering I need to get it down to 50% or even less.

I am currently setup in an unfinished basement, so it will be difficult to use an AC unit in such a larger area. Being at 25 Celsius, I may be able to use a portable heater...? I'm a first time grower so this is all new to me.

Here is a pic of my setup by the way, though most things aren't shown. 20210905_072020.jpg
 
Looking good!

Yeah VPD is handy for sure. On my latest grow, my humidity often teetered around 60% during late flowering on some days, which was risky -- but I was able to keep my temps high enough to maintain good VPD levels. I also had good ventilation in general so I was able to avoid mold and bud rot.

You do have room to boost your temps a couple of degrees with a heater, which would decrease your humidity a bit. It becomes a bit of a game between choosing the lesser of two evils lol.

I'll also say this: I'm a big advocate of oversizing exhaust fans. I run a 6" in my 2x4 -- many folks would call this overkill, but I like the extra extraction boost and it runs quieter at lower speeds. I feel oversized fans are a necessity in super humid areas (I'm in the Atlantic as well).

Good luck! :vibe:
 
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I run a 6” in my 4x2 as well. It’s been very humid here lately, which is unusual and I have one plant finishing. One thing I find that also helps is to put a fan in one of my bottom ports to draw some air in, it helps lower humidity a little and definitely helps circulate air around the lower portion of the tent.

I have an inkbird humidity controller that kicks my humidifier on and off. It also has a second input for a dehumidifier. I tried a small humidifier and it did nothing at all. So I plugged that fan in my bottom port into it. When it hits X humidity, the fan kicks on and starts circulating air and helping humidity drop more effectively than that little dehumidifier did.
 
Looking good!

Yeah VPD is handy for sure. On my latest grow, my humidity often teetered around 60% during late flowering on some days, which was risky -- but I was able to keep my temps high enough to maintain good VPD levels. I also had good ventilation in general so I was able to avoid mold and bud rot.

You do have room to boost your temps a couple of degrees with a heater, which would decrease your humidity a bit. It becomes a bit of a game between choosing the lesser of two evils lol.

I'll also say this: I'm a big advocate of oversizing exhaust fans. I run a 6" in my 2x4 -- many folks would call this overkill, but I like the extra extraction boost and it runs quieter at lower speeds. I feel oversized fans are a necessity in super humid areas (I'm in the Atlantic as well).

Good luck! :vibe:

So after opening up all vent holes and putting the exhaust (6") on 100% in my 4x4 tent, this is where I ended up (plus I watered yesterday): Hovered around 78 degrees and 66% humidity, when the lights turned out it dropped to 73 degrees and RH climbed to 72% overnight. This morning I'm at 77 degrees and 70% humidity. All dehumidifiers are going full and multiple fans blowing. My only other real option is to try a mini heater to raise the temp, otherwise just keep good airflow to avoid mold? What about going 24/7 with lights since I have autos?
 
So after opening up all vent holes and putting the exhaust (6") on 100% in my 4x4 tent, this is where I ended up (plus I watered yesterday): Hovered around 78 degrees and 66% humidity, when the lights turned out it dropped to 73 degrees and RH climbed to 72% overnight. This morning I'm at 77 degrees and 70% humidity. All dehumidifiers are going full and multiple fans blowing. My only other real option is to try a mini heater to raise the temp, otherwise just keep good airflow to avoid mold? What about going 24/7 with lights since I have autos?

Yeah I think a little space heater will help you. You could certainly run it on a timer to come on during lights out at the very least. Mine has 'low' and 'high' settings. Perhaps low during lights-on, and high during lights-off may be worth trying out. Of course you'll have to play around with the location and make sure it never gets too hot in your tent. But you seem to have room to bump temps up a few degrees.
 
Yeah I think a little space heater will help you. You could certainly run it on a timer to come on during lights out at the very least. Mine has 'low' and 'high' settings. Perhaps low during lights-on, and high during lights-off may be worth trying out. Of course you'll have to play around with the location and make sure it never gets too hot in your tent. But you seem to have room to bump temps up a few degrees.

You think it's safe to put inside the tent or will it heat the plants/pots too much? Should I put it outside maybe a foot away from one of my open screens?

I also just measured, it's 67% humidity in my basement so the air being pulled in is already fairly moist.
 
You think it's safe to put inside the tent or will it heat the plants/pots too much? Should I put it outside maybe a foot away from one of my open screens?

I also just measured, it's 67% humidity in my basement so the air being pulled in is already fairly moist.

You'll have to play around with the location of the heater. I keep mine outside my tent pointed toward one of my intakes.

Also, I'd focus on trying to get that ambient 67% humidity down more so than what's in the tent. If you can control that, it would be easier to dial in your tent vpd. How big are the dehumidifiers and where are they? Do you use any bigger, ~50 pint size dehumidifiers in your basement?
 
You'll have to play around with the location of the heater. I keep mine outside my tent pointed toward one of my intakes.

Also, I'd focus on trying to get that ambient 67% humidity down more so than what's in the tent. If you can control that, it would be easier to dial in your tent vpd. How big are the dehumidifiers and where are they? Do you use any bigger, ~50 pint size dehumidifiers in your basement?

I've got two smaller dehumidifiers, one is for 250 Sq foot and the other 550 Sq foot - both are inside the tent right now. I don't have any dehumidifier for the basement overall as it's just empty storage. Trying not to go too crazy expensive my first grow, but sounds like I might need more work.
 
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