Anybody experts good with CFM's

Here's the set up. Either a 5x10 or 5x9 tent with a vortex 750 cfm fan pulling through a 950 cfm filter. I'm going to push through the hood (I'm sold on pushing), so basically I'll have the filter on the floor with the fan on top of the filter pulling through the filter then pushing through the hood.

My question is about the size of the intake booster fan that will be on a bottom sock.

Should I use a:

6" booster fan rated at 160 cfm boosted to 250 cfm/ or 8" booster fan 300 cfm boosted to 500 cfm.

Any thoughts.

Edgar9 said:

Here's the set up. Either a 5x10 or 5x9 tent with a vortex 750 cfm fan pulling through a 950 cfm filter. I'm going to push through the hood (I'm sold on pushing), so basically I'll have the filter on the floor with the fan on top of the filter pulling through the filter then pushing through the hood.

My question is about the size of the intake booster fan that will be on a bottom sock.

Should I use a:

6" booster fan rated at 160 cfm boosted to 250 cfm/ or 8" booster fan 300 cfm boosted to 500 cfm.

Any thoughts.

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OK, two diff. questions here.
IMO, CFM vs area is one question, but CFM vs CFM is a whole diff. question.
As far as what you're asking, if your filter posted specs are greater than your fan specs, that is fine, the filter will not create excess resistance on the fan.
IMO, to pull air out, through the filter in greater quantity than the intake fan makes more sense, rather than trying to filter the fresh air as it comes in.
Do you have a stinky room?
Isn't the purpose of the filter to get the plant smell out before it permeates the room, not filter the room air before it gets to the plant?

Bakatare666 said:

IMO, to pull air out, through the filter in greater quantity than the intake fan makes more sense, rather than trying to filter the fresh air as it comes in.
Do you have a stinky room?
Isn't the purpose of the filter to get the plant smell out before it permeates the room, not filter the room air before it gets to the plant?

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I'm not trying to filter the air coming in. I'm trying to figure out how powerful an intake fan I'll need based on the specs of my exhaust fan/filter combo. Too little intake and there will be too much negative pressure. Too much intake and the tent will blow up like a balloon.

You should fire whoever sold you on pushing instead of pulling. Pulling is much more efficient.

well first of take Superstoner1 advice , but do as you will , So ok first thing you can put the horse before the cart , you need to know what size tent you will be using and also the Height of the tent , because you can no calculate the cfm you will need with out converting your footage in to Cubic feet . if you calculate wrong you will end up in the situation you are trying to avoid.as you state sucking in ten ,neg pressure ect ect .

here is a example 5'x10' room 6' in height = 300 cubic feet, so now that we know that we can size the fan

ok so we all no that fans are rated by size of inlet ,outlet and CFM , what does CFM mean Cubic feet per min


So now we know a 300 cubic foot room would need a fan rated for 300 CFM in order to move the air at a rate of ONE TIME PER MIN.

So not to get more involved here and try to make you understand the property of air movement , using your 750 cfm fan will be sucking in your tent walls like you stated, unless you make a passive area (opening of approx. 12 inch in round or 12'' x 12'' opening. NO passive fan will be required in your situation.

superstoner1 said:

You should fire whoever sold you on pushing instead of pulling. Pulling is much more efficient.

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I spoke with a few very knowledgable people today and I feel, and they do too, that having the fan right on top of the filter and then pushing through the hood is more efficient than pulling through the hood and filter. The reason being that the fan is most powerfull in that setup where it's right on top of the filter and I'll get the most out of my filter.

jrainman said:

you need to know what size tent you will be using and also the Height of the tent , because you can no calculate the cfm you will need with out converting your footage in to Cubic feet . if you calculate wrong you will end up in the situation you are trying to avoid.as you state sucking in ten ,neg pressure ect ect .

NO passive fan will be required in your situation.

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The first sentence of my post says either 5x9 or 5x10. I guess I didn't mention the height but they're both 7 feet. The cubic square foot difference between the two is basically nothing.

also, I disagree that I don't need an intake fan.

1. Because during flowering with the vents closed I need fresh air coming in, and
2. Because with the set up I described I'll have about 400 cfm coming out of the tent (starting with a 750 fan - 200 lost from the filter-150 lost from the ducting and hood=400 cfm's), therefore I need about 250 to coming in, otherwise there will be too much negative pressure. Keep in mind, once again, that during flowering the vents will be CLOSED.

That basically answers my question. I need the 6 inch intake fan with 250 cfm's.

Thank you.

That makes absolutely no sense. Any distance a fan has to push air puts more resistance on the fan. Take it from your "knowledgable" people or take it from real experience. Not to mention that you will have to double seal every seam on a reflector because it will have pressure in it.

Pulling through the filter then pushing through the hood is the best way to contain stink while also cooling a hood with only one fan.

The logic being there is only one ducting junction that could possibly leak unfiltered air to the intended stink free zone. You might push a small amount of clean hot air back into your tent if you have any leaks, but most of the heat is pushed out of the tent. This is preferred to stink leaks.

No intake fan is needed. Those tents are set up for passive intake.

superstoner1 said:

Take it from your "knowledgable" people or take it from real experience.

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Two of the guys I spoke with have been setting up tents/rooms for 15 years. They both said push. Another couple of guys said push too. I'm not sure of their exact background but they seemed knowledgable.

I also read up on the subject and came across a post from an hvac guy who said that fans are more efficient at pushing.

On top of that to get the cfm's right in the room I have to have the fan on top of the filter. The fan/filter combo works best with the fan right on top of the filter. Since I definitely don't want to pull through the filter after going through the hood there's only one way, to push. Filter-then fan-then pushing thruogh the hood.

Lastly, even though they're high speed fans and durable, it's better NOT to have hot air being pulled through a fan.

Cap'n Jack said:

Pulling through the filter then pushing through the hood is the best way to contain stink while also cooling a hood with only one fan.

No intake fan is needed. Those tents are set up for passive intake.

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I read just the opposite as far as odor control. If you pull, stinky air may get pulled in through the seems on the hood and then get exhausted unfiltered. If you push, any air that gets pushed out has already been filtered and would end up in the tent again anyway and would get filtered again.

Also, as far as the passive intake claim,once again, how would I use passive intake in a tent when all the vents are closed b/c I'm in flowering? I need an intake fan. A six inch intake fan to be specific.

It's strange. Most people on internet forums say to pull but everyone I've spoken to who works in the industry and sets up tents for a living (4 different guys) all say push.

Have you guys who are saying to pull tried it any other way? Or have you tried it just the one way, pulling, and you are not open to other options.

Who cares about pushing vs. pulling? My questions is why are you planning on wasting valuable floor space for a filter?

I "push it" every single time. Ever since charcoal filters came out! What i don't like about your plan is the filter being down low on the ground.. An 8" filter for that fan is huge, so i understand the dilemma. You didn't state how much wattage you are gonna run in that 4x8 tent.
Lets say your gonna run 1200w. I would rock the biggest cfm 6" fan + matching(little more cfm rating)filter. Hang that som bitch up high. Then use another 6" fan for intake, and dial it down, so you still have negative pressure. Do it all the time. Hang that filter up high though, please!

here is your answer guy

first thing your messed up with the filter ..........the filter and the fan CFM should always match so u get a even drawl tho the carbon
second thing u should run your fan on a varible speed controler allowing u more control
third thing your power intake as for balancing them this is almost a impossible task with out a wind meter (the bends the distance of travel and other factors to account for )

here is my best answer to help u
your carbon filter is going to be off at some point later when that 12 month mark hits replace it with one that matches this will make the math and the tent work better
2nd ok a 750cfm ............your going to need a anouther fan same size to feed the tent for your powered intake ....with a varible speed and u will have to tweak it to match as close as u can to it or i would leave it little high to have a puffy tent better light reflection and use all the area.................i am only doing some guess work but maybe a 6 inch inline fan would work with that on maximum and the other turned just above the low (guessing so if go off this get it from a place that allows returns/refunds)


and yah the filter is always the highest point in the tent to remove the heated air and smell/and to use the natural up draft effect of hot air vs cold air to get a even speard of fresh air/co2 to the plants to use