Is my room correct?

K1Ng5p4d3 said:

i really gotta disagree with what people are saying about passive intake being the best method. Now, im not super experienced, but from EVERYTHING ive read, its wise to keep fresh air flowing into your room ACTIVELY. Now, as far as the intake being smaller than the exhaust, your correct. I have a small 80 cfm fan for my intake, and a 540 cfm fan for exhaust/air cooling my fan. The only reason i bought this was because of all the shit ive read about it, both on here, and in books and magazines. All im sayin is, if Ed n Jorge recommend it, im fuckin doin it. Those motherfuckers are the rock stars of growin pot.

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if your exhaust is pushin air out than its flowin in too and your intake fan is hindering this if your movin 540 and putin in 80 you dont think it would pull 80 without that fan it will probably pullin more y do you need an intake fan

Scenario two : same room, 200 cfm 6" exhaust, 12" passive intake. Because the intake is much larger than the exhaust, no restriction is put upon the exhaust fan and it can effectively move it's rated cfm. This uses less power and cost less initialy than scenario one due not using 100 cfm fan.

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For one, this study doesn't tell me anything besides someones opinion. it says it cost less but it doesnt say anything to scientificly back it up. like total CFM would be a good one to start.

for two, i dont care how many studies about air movement you show me. There is what books say and then there is what happens in the grow room. two totaly different things.
i tried having a passive intake, and it does ok, my temps were 7-9 degrees above house temperature. then i put an intake fan in, half of the cfm of my exhaust, now my temps are 3-5 degrees higher than house temps. inefficient or not, they do work better than passive.

been following this thread and in my opinion is this. if you can get away without an extra fan do it. passive is best if you can make it work
i myself have an intake that is as big as the exhaust. i then restrict the intake flow until i can cause constant negative pressure on my separate rooms

lolipop crop, it isn't a study. It is three, hypothetical scenarios, given to show differences between common setups. I wasn't referencing anything. You want total cfm? Do the math. It's all right there. Hypothetically. Not many people, myself included, have proper testing equipment to measure ACTUAL airflow throughput in their growrooms. All my info given was absolutely my opinion. I'm happy adding an active intake helped your problem. This is anecdotal evidence. I too have tried both ways, and found more air moving out, with an appropriately sized passive intake, prferable to having a half-sized intake fan. I prefered it because my killowatt told me I was using 90 less watts, and my temperatures are as low as with any scenario. My opinions stated were the result of these trials and are not exact replications of my findings. I used arbitrary numbers in my given examples so as not to create math issues for some readers.

If an active intake were needed, every fan would have two sets of impellers, one exhaust and one intake. Hooking up six, 300cfm blowers in series will not produce 1800cfm. Hooking the same six fans parralel will produce that much airflow provided the intake hole is large enough, and therer is sufficient space within the room for that volume of air to move unhindered.

I'm not going on what growbooks say, this is physics, and I can't see a way to cheat it.

K1Ng5p4d3 said:

why are intake fans bad?? passive air intake is no good, and if you have an exhaust in your room, your going to want to cycle in new fresh air while used up air is going out. Why would you say that an air intake fan is a nono??

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Take a sealed box. Mount an exhaust fan so it can only take air in through the box. Turn it on. Feel that flow? Now cut a hole the same diameter as the fans ports or larger on the box. Feel that flow? If your fan is quality, and designed to operate with pressure, all the air it needs will enter the box due to suction. The only thing that can impair that flow is resitance. Placing a smaller sized fan on the intake creates resistance. Perhaps in your case, adding the intake fan created LESS resistance than your passive intake and this is why you achieved lower temps. This is IMO due to not having an appropriately sized intake hole.

Does your central a/c system use a seperate intake fan on the return side? They generally use one properly sized blower, connected to appropriately sized ducts so resistance is negligable to the result. Only on long runs of resistance creating ducts are booster fans used, which can often be avoided by using two sizes larger duct than the needed cfm of air movement.

The pressure:resistance ratio is the only factor which will lessen the efficiency of a system.

So to sum up my arguments, properly sized passive intake is good and maximizes efficiency. Active intake is bad, as even if you achieve the same cfm as your exhaust fan is rated for, and cool to the same temp, you have done so with additional watts used. Therefore a lack of efficiency has occurred. If there is a "failsafe" argument to be made regarding having two fans instead of one, it does not become impeded by placing both fans on seperate exhausts. This in fact increases your total suction against the intake and creates more airflow. For the record, anyone using more than one extraction fan should also have one way dampers on each to only allow your air to enter your , hopefuly, filtered intake.

For the record : I am not trying to single you out and pick on you. I just want to help people run efficient grows. If something that takes power can be eliminated, each of us should do it. For all it's about green, environment concerns or money concerns.

tusseltussel said:

....... e s ...... you just gotta get that damn aluminum foil out of your room

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When did I ever say I have aluminum foil on my walls?

lolipop crop, it isn't a study. It is three, hypothetical scenarios, given to show differences between common setups. I wasn't referencing anything. You want total cfm? Do the math. It's all right there. Hypothetically. Not many people, myself included, have proper testing equipment to measure ACTUAL airflow throughput in their growrooms. All my info given was absolutely my opinion. I'm happy adding an active intake helped your problem. This is anecdotal evidence. I too have tried both ways, and found more air moving out, with an appropriately sized passive intake, prferable to having a half-sized intake fan. I prefered it because my killowatt told me I was using 90 less watts, and my temperatures are as low as with any scenario. My opinions stated were the result of these trials and are not exact replications of my findings. I used arbitrary numbers in my given examples so as not to create math issues for some readers.

If an active intake were needed, every fan would have two sets of impellers, one exhaust and one intake. Hooking up six, 300cfm blowers in series will not produce 1800cfm. Hooking the same six fans parralel will produce that much airflow provided the intake hole is large enough, and therer is sufficient space within the room for that volume of air to move unhindered.

I'm not going on what growbooks say, this is physics, and I can't see a way to cheat it.

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I agree with you on most of what you are saying. Probably would be more efficient for me to plug a bigger hole for a passive intake in my wall and run two exhaust fans, I'm only defending the fact that an intake fan will help, and will not in any way hinder the performance of an exhaust fan unless you use less than about 25% of the CFMs, above that it will help move more air. If we were grwing in a sealed box then you would be right, because the exhaust fan would only be able to get air thru that one intake. We need to take into consideration every nook and kranny that the exhaust fan can take air from. If it can have less resistance because an intake fan is feeding it some air, it can use that energy to pull more air from other places. No its not the most efficient way, having them both as exhaust fans would be the most efficient, but it does help. If i didnt have my carbon filter and my fan all matched up and ducted out i would think about switching to a better passive intake system, but like some others too i am stuck with what i have, and putting in an intake was the best option for me at the time.

Put that 25% back in your ass..... you're not even trying to be logical.

Ya know what... Marijuana is a weed... no matter what... as long as it has some air... some good soil... some water and some good lighting. you basically wont fuck it up... so why does it matter so much about a god damn vent and all that shit...

WHO GIVES A FUCK!!!! not me, thats who....

Why does it matter?... because dude started a thread.... that's why it matters. You give a fuck enough to leave a comment and whine all over it. Marijuana may be a weed to the you and the lawmakers, but it certainly ain't a nuisance to me and I have the utmost respect for Mary Jane..... a weed!?! fuck that.

E S said:

Put that 25% back in your ass..... you're not even trying to be logical.

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whenever u speak anything against my beliefs i know im on the right track. You're a fuckin joke. I'm telling you from what I have experienced not about what I read. Go get some grow time in, then come fuck with me kiddo.

I aint got an intak or an outtake fan, just an osilating fan in a small room, with a vant to the outside, and that seems to work for me...

LolipopCrop said:

whenever u speak anything against my beliefs i know im on the right track. You're a fuckin joke. I'm telling you from what I have experienced not about what I read. Go get some grow time in, then come fuck with me kiddo.

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Aw..... man, look..... you're bleeding all over yourself.

Baz said:

I aint got an intak or an outtake fan, just an osilating fan in a small room, with a vant to the outside, and that seems to work for me...

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So far thats what I have also.A A/C keeping room temps down,little Wal-mart fan blowing air across the plants and a small dual exhaust fan in the other window with a few strips of activated carbon on the fan to control odors.Worked wonders for me lol.

WOW... it's amazing how some people can be so rude to people they hardly know...

I guess some people are just like that though... that's too bad... it always takes away from the learning experience....

Oh well...

As far as the fans go, I can see where the intake is not necessary in most applications....

I have one.... and I love the fact that I can use to regulate my temps even more accurately...

I have a 6" 440 CFM exhaust and a speed controlled 6" 440 CFM intake, dialed down to about 330 CFM.... both attached to a thermostat...

I use the intake to bring in fresh air from the outside world... across the room... with all that ducting, and the bends along the way... I am actually saving my exhaust fan some labor...

And I get to have my cool tubed 600 watt HPS ten inches from my plants with complete control from 65F to 95F...

Not only that, if I build another 36x20x60 tent (like I have now), I will e able to use the same fans to power both tents...

19,000 lumens/sqft... @ 75F, seems to make it worth to me...

But everyone has a different situation...

And there are certain situations where it is not needed, even though it wouldn't hurt anything...

Landragon said:

he does act like an ass when people disagree, but in this situation, he's also correct. For EVERY situation, a passive intake is the CORRECT way do ventilate. Ok maybe if you had flow meters on your ducts linked to. Computer which controlled fan speed, yada yada.... But again, this , um, "de efficient izes" the room.

Scenario one : 300 cubic foot room, one 200 cfm blower exhaust, one 100 cfm blower intake. Generaly this means a 6" exhaust and a 4" intake. Obviously this creates a restricion on the 6" end fromthe 4" end. Even if both are 6", this means the exhaust fan must suck air around two sets of fan blades, it's own, and the intake. This is helped by the push of the intake fan.

Scenario two : sake room, 200 cfm 6" exhaust, 12" passive intake. Because the intake is much larger than the exhaust, no restriction is put upon the exhaust fan and it can effectively move it's rated cfm. This uses less power and cost less initialy than scenario one due not using 100 cfm fan.

Scenario three : same room, both fans on seperate exhaust holes, 12" passive intake. Similar to scnario two, with roughly 50% additional flow through.

It is easy to see which system is the inefficient one. Why you would choose to do anything less than efficient is beyond me. And the facts are, putting a smaller diameter fan on intake than exhaust places a restriction on exhaust which limits efficiency, and using a larger or same sized intake makes maintaining negative pressure in the room a chore which could lead to odor leaks.

To the poster who said they need an intake because of all the leaks : build a better growroom. Air leaks are a prime source of pathogen entry. And light won't bend corners, but it can leak in or out of those "leaks".

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Could you explain this more in depth please? Perhaps with some images to show your point? I'm interested in this, but don't quite follow everything here.
Thanks

EDIT: You explained it again in a later post on this. Thanks. The box example helps visualize this. Is there any kind of testing equipment you can buy/rent to measure air flow?

Ive found this an intresting thread. I Dont know much about this topic but feel more educated on it. Rep given to those i thought gave good advice.
Shame about the children agruing but boys will be boys

This is a good thread. From what I had read I didn't think an intake fan was useful but I can see now that it may be useful to reduce temps.

The intake fan and temp depend on the room. How are you getting your air? Is it through a hole in the lower part of the wall or are you actually getting ambient air in the room? Do you have environmental control devices in the room or not... Those questions will change a whole bunch of scenarios. The majority of the time you would want a controlled negative pressure inside your "area" to control the flow of air and odor. If your ambient room temp is 68* and the temp in your "area" is higher you might consider adding a few CFM (much smaller fan active intake) and having a passive intake, just be sure to not have the combined surface area of your active intake and passive intake combined be no more than 2X the size. Plug up some of your passive intake if need be. Another solution might be to clean up the restriction on your venting or increase the CFM of your exhaust fan to pull the proper amount of air for your "area". Be sure you follow the general rule of 2X the area not diameter for intake than exhaust. There may be a bigger problem causing your air temp. Pulling passive air from a room at the proper rate and push-pulling at the proper rate will cool the same all together because your cooling source is the same as long as the calculated flow thru CFM is the same in the two situations cooling will be the same. Do what feels right to you and what works on your personal setup.

As suggested research flow dynamics. I work in HVAC and may have some experience in this.