What's a good first setting for grow tent fan?

Just installed a Marsh-Hydro 4" carbon filtration system on a 3’x3’x6’ tent.

What’s a good starting point setting once flowering begins just to try to get the stink out of the house?

Negative pressure in a closed tent is what you should be shooting for to prevent smell from escaping.

Enough to ensure fresh air circulation and proper humidity and temperature.


I have a small fan blowing in from a bottom port… does that make it harder?

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For a negative pressure zone you need the main fan pulling more air from inside the tent than the little fan pulls in. This is easy to tell, are the sides of your tent pulled inwards? If so you have a negative pressure zone.

Your ventilation system should have come with a booklet with a few examples of setups for neg zones using the filter for 0 external smell.

Also remember to have to open ports opposite one another to help circulate the air. If your current interior fan can oscillate that will help move the air more and even out temps and RH through the tent.


Here’s a pic of my tent, not the same size as yours, but will do for reference. I have my main fan pulling from the top port and the bottom back port is open on the inside for the intake. I have a carbon filter for mine and can easily attach it after my fan for any smells if they become an issue. If you have the room can also mount it all inside. I have mine set in 1 but it’s a 6” fan for a 2x2x4 tent. On a 3x3 would have min of 3.

At the top of the pic can see the big fan on top of the tent.

Can see the open port just behind the plant for intake.

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Mount your exhaust fan top of the tent if not already. open the pass through hole at the bottom exhaust fan will pull an exhaust hot stale air out and also pull fresh air through the pass through hole an maintain negative pressure on about medium speed. Good luck

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@kellydans @MidwestGuy @The_Cannabowlist

Thankfully, I set it up that way. Intake on bottom exhale on top. I also did the pressure test on the tent sides and a fan setting of about 5 (of 10) sucked it in noticably.

Thank you so much. I feel pretty good about it now. Cause the stink will be a comin’ in about 3 weeks or so and me gots to get a ready.,:sunglasses::fire:


Here’s my final setup. I did change out the dryer hose because this one leaked air. ,