Balancing Temp/Humidity with Exhaust Fan

MY QUESTION: Based on my setup as these plants start to slowly grow I feel like I am going to have to start running my output/carbon filter fan(I can’t remember make/model but it’s the standard one w/ VIVO sun tents) which I have not been doing as of yet.

*The issue I see after I run it on the lowest setting for 5-10mins is that the humidity significantly drops(45-55%) as all that water is being sucked up and away from the humidifier to top of the tent/carbon filter. Is this not so much an issue during this seedling/early stages then it will be going into Veg? Should I be less worried about CO2 circulation at this stage?
I hope this makes sense.

MY SETUP:So I’m currently growing (3) White Widow Autoflower about 2wks, in a 2X4X6 grow tent in a dry finished basement in the Northeast.
-68-74% Humidity w/ a adjustable % humidifier.
-Small space heater on a adjustable timer at around 72-75*
-1 Clip on fan inside and 1 small fan outside blowing in fresh air through half of the square intake at the bottom.

  • Spider-Farmer SF-2000(200W) LEDs

do you need to run it? i run mine to keep the temp down and crank up my Humidifier.

You have to move air in out , positive and negative pressure , take the oxygen stale air out and bring in more fresh cool air into the tent . You have your inline fans setup , shoukd help balance the tent out !

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First I would say unless you have a smell, which being that young you shouldn’t, take off carbon filter, I only use mine the last month or so. I live in a Illegal state with noisy neighbors, If you have a fan in there blowing on your girls to keep them healthy and a fan blowing in fresh air, try to open up a side vent in your tent, to help keep fresh air circulating. I have a few seeding now, and a 1 month old, and haven’t even turn on in-line fan yet for reason you posted drops my humidity to low.

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This: high humidity (that you have) will cut down the life of the carbon filter. Better to run only when you need it.

Seedlings will obviously not need the amount of air exchange a more mature (and larger) plant/plants require. A circulating fan would be more helpful at this point.


Your setup sounds almost identical to mine. The controller can’t really manage your heat and RH at the same time, one will win at the expense of the other. In fact a duct fan won’t be able to help manage your RH very well at all, unless you want to lower it.

I have a second controller running the humidifier in my veg tent. And it’s a big one, fed from a 55 gallon tank of RO/DI filtered water. Two smaller ones got me to like 40% with the exhaust going. Lower than that and I was running into issues later in veg.

I’ll also add my vote to the “no filter during veg” advise. I had to get the RO filter because I kept fouling my carbon filter due to the hard water buildup. And I’ve got pretty clean tap water - 140ish ppm TDS.


I assume you are flowering if you need to use a carbon filter.

Consult a VPD chart, you’ll see that once you start flowering your plants the humidity needs to be in the 40-50% range. That might make your life a little easier.


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On point with removing the filter! Likewise here :love_you_gesture:

Thanks for the quick response here! This helps a ton. That VPD chart is new to me so I’ll just use that as my baseline and wait to turn on the carbon filter/output until flower.

do you know anything about a good power source controller that can work remotely with an app? I want to operate a fan, humidifier and water pumps

Titan controls have many options !

I think AC Infinity had a new controller that does all that minus the water pump part. No electricity parts there it’s all water pressure. There’s a float in my rain barrel. You might be able to find some type of valve if that’s what you were thinking. I don’t think the controller does that.

Thank you