Tent Ventilation Question - CFM for active intake.

My tent is about 240 cubic feet. I am planning on using a 400cfm rated inline fan with a 400cfm rated Phresh carbon filter and a speed controller to dial it back a little.

I'm looking for a booster fan to use for active intake. It will have a Phresh intake filter on it. Also, there will only be about 4 feet of straight ducting the air is being pushed though into the tent. The passive vents on the tent will remain closed btw.

Booster fans are rated in "free air" and "boosted" conditions. Given that my goal is to pull about 300cfm though the exhaust, would my intake fan rating be free air or boosted?

I'm looking at one fan that is rated 300 free air and 500 boosted. And another that is rated 180 free air and 250 boosted. I think the 300 free air would be perfect but don't want to be pushing too much air. My current thought it to use the 300/500 booster fan with a 270cfm rated intake filter, would this be a problem for the fan or filter?

Thanks!

AlGore said:

My tent is about 240 cubic feet. I am planning on using a 400cfm rated inline fan with a 400cfm rated Phresh carbon filter and a speed controller to dial it back a little.

I'm looking for a booster fan to use for active intake. It will have a Phresh intake filter on it. Also, there will only be about 4 feet of straight ducting the air is being pushed though into the tent. The passive vents on the tent will remain closed btw.

Booster fans are rated in "free air" and "boosted" conditions. Given that my goal is to pull about 300cfm though the exhaust, would my intake fan rating be free air or boosted?

I'm looking at one fan that is rated 300 free air and 500 boosted. And another that is rated 180 free air and 250 boosted. I think the 300 free air would be perfect but don't want to be pushing too much air. My current thought it to use the 300/500 booster fan with a 270cfm rated intake filter, would this be a problem for the fan or filter?

Thanks!

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well IMOP .. i would just use yor exhaust and instead of running passive intake get a HORTI dust filter and force all the in air to come through that..theres zero cfm loss on incoming air.. then your only running one exhaust fan.

that filter blocks the mold spores and crap coming in but like i said theres zero cfm loss so if you run a 4" exhaust dialed back a bit you can get a 4" horti dust and attach it to one of the little flaps coming into the tent... that would completely accomplish your incoming air filtration and stop you from having to spend extra on fans/electrical.. etc..

from the way it sounds like your talking about hooking it up you could have CFM loss issues.. especially if he only incoming air point is the passive system.. which i assume is the case other wise its pointless... you'd have to balance it right with the same CFM to not have negative pressure being created.

phil k said:

from the way it sounds like your talking about hooking it up you could have CFM loss issues.. especially if he only incoming air point is the passive system.. which i assume is the case other wise its pointless... you'd have to balance it right with the same CFM to not have negative pressure being created.

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Hey, I'm a little confused. I think you meant to say active instead of passive in a couple spots, hehe.

It sounds like you are suggesting not using an active intake fan but instead put a filter on a port and use that for air intake, correct? That way I can have filtered incoming air but not have to use a booster fan as well.

That seems like a pretty good idea to me!! I suppose I could even do the same with a phresh filter instead of the horti one if I want. For the same money, the phresh ones seem better despite needing to be replaced more often.

AlGore said:

Hey, I'm a little confused. I think you meant to say active instead of passive in a couple spots, hehe.

It sounds like you are suggesting not using an active intake fan but instead put a filter on a port and use that for air intake, correct? That way I can have filtered incoming air but not have to use a booster fan as well.

That seems like a pretty good idea to me!! I suppose I could even do the same with a phresh filter instead of the horti one if I want. For the same money, the phresh ones seem better despite needing to be replaced more often.

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yep they are horti dust filters.. i run them on all my intakes in my rooms.. and in my clone tent.. i do the same in my clone tent...i have a 4" exhaust with carbon attached to it sucking the air out .. very slightly dialed back to kill the noise a bit.. .the incoming air port has the horti filter attached to it. and all my other incoming air parts are sealed up so the airs coming through the horti filter... same with my grow rooms but i run 6" and 8" in my regular rooms

its much easier that way cheaper as well

get bigger fans than you think you'll need and plug them into speed controllers. i would recommend active intake because negative pressure in your room is a big no no, and in order for passive intake to work you would need to create negative pressure with your exhaust fan. active intake with a speed controller gives you full control over the pressure in your room. it's impossible to have this level of control when running passive intake.

for my 4x4 tent i had a 440cfm inline fan for exhaust and two 240cfm booster fans connected to each other and to a dust shroom (filter). the pressure in my tent was perfect and i didn't have to run my fans at their full capacity 24/7.

yeah for sure you can do it that way too. but you really don't need the intake fans.. you could run the 4" exhaust and a 6" shroom filter and not have any negative pressure issues or intake airflow issues .. if the fans moving say 400cfm.. its still going to pull that in through the shroom without help

but ion the flip side CCC has another great point using a powered intake can allow you to quite down your exhaust

In my 4x4 and 4x8 tents I use a 440cfm hooked up to a phresh filter, sucking air in the tent, through the light to cool it, and out the window. No need for intake fans for a tent if you use the passive intake flaps (or create them). Tent walls suck in a bit which is great, negative pressure means all the smell is going out the window (until you open them up!)

Forest, My biggest thing is, I didn't really wanna use the passive intake flaps and rely on just the bug meshes as I don't have a super clean area to pull air from. So I want to use at least a shroom/phresh(intake)/hepa filterd port.

After talking to the dude at the store I opted for the 300cfm(free air) booster fan. It was only $35 and I can choose whether or not I wanna use it. Only down side is I can't hook it up to a speed controller but I'm sure it has was less balls than the 400cfm proper inline fan, which is on a fan controller so I should be able to dail in equal or close to equal pressure.

I think I'm gonna actually shoot for a slightly positive pressure if that booster has enough power to pull it off. I realize what this means for smell, but the vast majority of the air will be filtered and the grow is in a spot where smell is not 100% critical.

I've got just about everything for the grow. Gonna post in my other thread about it, I just made this one to get some quick responses before heading to the store yesterday, hehe.