I started a thread on controlling VPD and somebody mentioned something about intake fans on their tent. I have Cloud line exhaust fans on both my tents and flexible duct pipes to a filter box for intake. My intake comes in the bottom of the tent in my exhaust goes out the top. I don’t really feel any suction but I have to assume the air is going somewhere. Do you guys have intake fans on your systems as well as exhaust fans
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No intake for my 2 tents. I have 2 3x3 tents and each has a 6 in exhaust fan. The exhaust fan alone is enough to create negative pressure (the walls of tent look sucked inward)
I wouldn’t think you “need” a separate intake fan but I suppose it would also depend on size of exhaust fans/size of tents. What are the fan sizes and the dimensions of your tents?
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I prefer to use both intake and exhaust fans, and run both with speed controls. This makes it very easy to adjust air flow through the tent, and easy to set set tent pressure to slightly negative for odor control if needed. This set up is great if you make any changes to the ducts or such things. For example if you added a better intake filter. You could simply speed up the intake to overcome the added restriction of the better filter.
I know some here will disagree. But I started down this path because I hated the way the tent sides suckled in with just an exhaust fan. I have not regretted adding this system on two tents to date.
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I have a fresh air intake but im in a 12x8 room. I just use it to help cool at night and bring in “fresh air”
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I’m too small. Right now I’m running autos in a 2x4 with a 6" exhaust and all the bottom vent flaps off. The last thing I need is another fan 
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Everyone finds their way to do things, and if it works for you, then that’s the right way…for you!
Shun the disbelievers… shun, shun!
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Couldn’t agree more @Mr_Wormwood . “System balance” is a very personal thing.
What works for someone in the high desert, isn’t going to be the same for someone in the PNW.
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Speed control is the key in balancing fans the your tent size. If your 2x4 is six foot tall that will be 48 cubic foot. The ideal air flow for a complete change of air every two minutes would be about 25 cfm. I would not try to force more than a complete change of air then one minute, (50 cfm). Or no less than a change every 5 minutes. After all if air velocity through the tent becomes so great you do gain any more heat exchange. Because the the air is moving too fast to pick much additional heat. A speed control on that 6 inch exhaust with a 4 inch intake fan with speed control would allow to dial in the exact air flow.
Don’t take my word for it. Take a look at AC Infinity’s fans they all come with built in speed control.
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Oh man, way too early to be throwing math at me
Well then, I guess that I will forget about sharing the formula for flex duct resistance per foot. But seriously, if you don’t crunch some numbers it is just guesswork.
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Yeah I really am a fly by the seat of my pants kinda guy and math is unfortunately not a particularly good friend of mine.
I can certainly appreciate how it simplifies things for people that are good at it, but it confounds my primitive brain
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Oh, I don’t know if it’s just “guesswork”.
My temps &/or humidity dictate most of my fans speed and runtime until flower.
Even then, when it’s running 24/7, it’s still heat/hum that dictates speed.
All the cabin exchange HVAC numbers just work themselves out in the background.
Just a different angle of approach to control the climate I guess. As long as the climate is controlled, it’s all good 
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Sounds like you have your grow dial in very well. There is enough info out there these days that the math is not necessary anymore. Let me change that to this. Without the math you maybe looking at more trail and error.
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No, because:
-An intake fan will reduce the passive intake area, & most exhaust fans already need multiples of their own port size in passive intake area, in order to reach max flow at 100% power.
-Fans in series are always going to fight each-other.
-Intake fan could end up pressurizing the grow area, potentially causing odor leaks.
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I knew that this disagreement would be coming from you. All I can say is that I have tried both ways, and wouldn’t go back to just an exhaust fan. I have asked you this before and never got a clear answer. Have you ever tried running both exhaust and intake fans before?
Again speed control will let you to balance the air flow, and prevent the fans from fighting each other.
I use both intake and exhaust fans. I condition the lung room with and AC and dehumidifier or humidifier and use the intake fan to bring fresh air in the tents while the exhaust fan exhaust the stale air 
When I made my first box more than 20 years ago, I was trying to increase airflow by stacking exhaust fans on top of each-other in series. I also wasn’t providing them with enough intake area. I think I started off with a 4" intake hole for a 4" fan, lol. Basically the same setup as running an intake fan & exhaust fan of the same size in series. Same inefficiencies. Then I learned some very basic things about fluid dynamics & airflow, & realized that it was a very inefficient configuration for a number of reasons, & that I needed to run the exhaust fans in parallel & also provide them with enough intake area for them to reach max flow at 100% power.
Speed control won’t prevent fans in series from fighting each-other. One reason is that the fans are still physically in the way of each-other, taking up port area & causing turbulence.
Also, I’ve flow-tested my own fans, & they all want to see more than their own port size in intake area to reach max flow at 100% power. One was around 5x, one was around 3x.
So if one exhaust fan needs more intake area than its own port size to reach max flow at 100% power, & if you’re starting out with the same-sized hole (already too small) or smaller for your intake area, then further reducing the size by putting a fan in the way is making it worse. If someone is saying things like they have very high velocity through the intake port, or a tent strongly sucking in the walls, that all points to an exhaust fan that is restricted somewhere on the intake-side of the fan, & simply asking for more intake area.