Do I Need An Intake Fan?


Setting up a tent for my first indoor grow (previous grow was outside). I have a 2x4 AC Infinity Cloudline T6 exhaust fan.

Do I need an “intake” fan to bring in fresh air and not suck the sides of my tent?

How big? What size?

Recommendations appreciated.

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I would. I use a 4” inline duct fan on my smaller grow tents and a 6” on the larger. Helps bring in fresh air plus the benefit of cooler air from the lung room :love_you_gesture:


I run a 6" exhaust fan on medium speed with a couple of pass through holes at the bottom of the tent open to pull fresh air 24/7 Also to circulating fans , never had a problem. Pretty much a preference you can go either way . Happy birthday @OGIncognito


Right on Brother and appreciate the BDay wishes :love_you_gesture:


What are pass through holds?? (Above reply)

How do I tag someone’s name??


Use the @ symbol before name @Doug79
( Holes) Most tents come with 3 or 4 holes With pucker string at the bottom of the tent.
Good luck :v:


Speaking from experience here. I would get another T6 AC Infinity fan. While is true, that both fans will be running at minimum speeds. But, what a great reason to move to larger tent in the future. I could see myself telling the wife.
“Hey Baby, I already have the fans I need for a bigger tent, and the fans cost more than the tent.”
But seriously, it is good to keep in mind where you want to be in the future. It will be cheaper to buy an oversized fans or lights once. Rather than two different sized ones.
I prefer an intake fan, along with the exhaust fan, provided that both have speed controls. I like to be able to control the tent’s pressure with the fan speeds. After all, you only need a slight negative pressure for odor control. But, on the other hand a slight positive pressure will help keep your tent cleaner.

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No, you would just need more intake area.

@PhotoFinisH , You keep advising people not use an intake fan. Just curious, have you actually tried an intake fan yourself?

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My tents are in dark rooms in my basement so I just leave one of the screened vents open and have never felt the need to increase ventilation by having an intake fan.

If I was growing in a bright environment I would probably use an intake fan to keep light leaks from interrupting flowering.

If doing a Passive air system which is what i do myself, it is best to have twice the size of exhaust to keep the fan from choking or to keep negative pressure down a touch. For example, i use a 6 inc exhaust so i have to different 6 inch ducts coming out of tent down low, with a curve on them to restrict light from entering. Always bring your cooled air down low so the heated air thats rising can be sucked out up top. Good luck. Ps, air intake fans are nice too, bc u only need one duct in that case but me personally finfmd it unnecessary

I have a 3x3 and also a closet. I have filtered intake fans on both. I use them as another source to move air, filter what goes in, and of course bring in cooler lung room air.

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Fans inline are what I don’t like to see, & usually I end up suggesting not running an intake fan since I want a little negative pressure to keep up the velocity moving through the passive intake, & keep the smell in. On my larger cab I run a dust filter & a light trap chamber on my passive intake, but it’s all oversized to try & keep the flow up.

At least 2x. On my larger cab, my intake area got to around 5x the area of my fan intake port before I lost negative pressure. I get a little back when I install the oversized light trap/ filter, so I know I’m still right around max flow, with a little velocity on the intake air, & keeping the smell in.

I have added intake fans on two tents now, and I like this much better than just an exhaust fan. The addition of speed controls on each fan, will enable one to adjust the amount of air flow through the tent. As well this makes it very easy to set the tent’s pressure.
My only regret is not knowing about the AC Infinity fans that come with a speed control sooner.
Of course it comes down to what works best for one’s own grow area. For example the walls sucking in on my 5x5 is not a big deal. But it is a problem in my little 2x3 though.


Independent controls, Exhaust speed greater than intake. Single control (Cloudline 67) controller two with same program. T6 Exhaust T4 intake Or as Ickey, said, T8 and T6 Future expansion covered.

To me, optimizing the tents pressure is getting near max flow at 100% fan power, but staying just under static pressure. Anyone can get there - or static pressure if they want to, by dialing in the passive intake area.

If your tent is fully set up & still sucking in the walls, the exhaust fan is telling you that it can flow more, & all you need to do is give it more passive intake area & it will flow more.

Speed controllers still work on a single fan. My temp controller has two selectable slopes so the fan starts off slowly & ramps up to full speed if necessary. But if the intake area isn’t dialed for (near) max flow at 100% power & ends up too small, then flow will be restricted at the higher speeds at least.

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@PhotoFinisH, your problems with trying to control two individual fan speeds with one controller is with the controller inputs. For a controller to do this correctly it would need a couple inputs reading static pressure, also the “can programing” that is in an AC Infinity controller is not programmed for pressure input.
The simple solution to this would be to use manual speed controls to set each individual fan speed. This would allow one to easily set the amount of air flow or tent pressure. Then let the controller cycle the fans on/off by time, temperature, and or humidity.
Again, it comes down to one’s individual grow area conditions. My lung room maintains a petty constant temperature, and this solution would work very well. But on the other hand if the lung room temperature had wide daily swings in temperature this wouldn’t work very well.

I’m not trying to control two fan speeds with one controller, but don’t worry about it. I’m talking about maximizing the flow of one exhaust fan & minimizing the obstructions. The pressure would be “set it & forget it” when optimizing the airflow through the cab with the exhaust fan at max power, & targeting for near max cfm, with a little negative pressure on it for some velocity at the passive intake. The pressure should end up at just under zero static pressure then.