Inline Fans INFO NEEDED

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Will5437

Active Member
Hello
I am running a 4 ft by 2 ft by 5 ft
I was wondering what kind of fan do I need to exhaust the air, as well as pull it through the inline filter.
What is the cheapest fan that will get the job done?
 
IndicaFatnHeavy

IndicaFatnHeavy

Active Member
well... a fan that can pull out ur cubic feets per min. (CFM) find out ur cubic footage... i forget how to.. im so fuckin ripped.
but remember. to get make an inlet.. and get intake int othe grow box(another inline fan facing the other way)

1x inline fan to exhaust
1x inline fan for intake.
and a inlet for the negative space

thats if ur using that grow set up
 
K

KushHaze

Member
IndicaFatnHeavy said:
well... a fan that can pull out ur cubic feets per min. (CFM) find out ur cubic footage... i forget how to.. im so fuckin ripped.
but remember. to get make an inlet.. and get intake int othe grow box(another inline fan facing the other way)

1x inline fan to exhaust
1x inline fan for intake.
and a inlet for the negative space

thats if ur using that grow set up
Click to expand...
Take the length x width x hight(depth)= cubic volume. Hope that helps a little and good luck ;-D
 
tea tree

tea tree

Well-Known Member
Man from my expereince you want a six inch inline that pulls at least 400 cfm! Lol, I tried less and no way. I live in the desert but with the ac keeping it cool that is the only way to do it.
 
Hairy Bob

Hairy Bob

Well-Known Member
Depends on the intake temps really, if they stay below 75 I'd say 150-200 cfm would do, but you can't skimp on ventilation, it's what stops your babies cooking!
It is far easier to manage temps if you get a fan bigger than you need, then run it on a fan speed controller, thermostat, or both wired in parallel so it runs at say, half speed until the temp rises and the thermostat gives it the full juice until it cools down again, rather than have a fan that will just about keep it within acceptable ranges running flat out the whole time the light is on.
Also, intake fans are COMPLETELY UNNECESSARY. At best they waste energy, by moving the same amount of air that would flow into the growroom from the exhaust fan lowering the pressure. If the intake fan were too small, it would restrict the amount of air that could flow in, too big and it would raise the pressure, creating odour leaks and possibly raising the temperature (with any gas, if you raise the pressure the temperature rises, air is no exception).
 
W

Will5437

Active Member
Hairy Bob said:
Depends on the intake temps really, if they stay below 75 I'd say 150-200 cfm would do, but you can't skimp on ventilation, it's what stops your babies cooking!
It is far easier to manage temps if you get a fan bigger than you need, then run it on a fan speed controller, thermostat, or both wired in parallel so it runs at say, half speed until the temp rises and the thermostat gives it the full juice until it cools down again, rather than have a fan that will just about keep it within acceptable ranges running flat out the whole time the light is on.
Also, intake fans are COMPLETELY UNNECESSARY. At best they waste energy, by moving the same amount of air that would flow into the growroom from the exhaust fan lowering the pressure. If the intake fan were too small, it would restrict the amount of air that could flow in, too big and it would raise the pressure, creating odour leaks and possibly raising the temperature (with any gas, if you raise the pressure the temperature rises, air is no exception).
Click to expand...
Thanks guys.

This site really has not that much info on ventilation as much as other things
Is 4 inch inlet really that large? The inlet temps are really low, the duct gets cold to touch. I saw a 135 cfm can at menards, and I think i might hook that up to my scrubber.
 
W

Will5437

Active Member
Hairy Bob said:
A four inch inlet isn't really that large, but then it depends what you're comparing it to.
As for the site not having much info on ventilation, there's a whole section on it in the faq https://www.rollitup.org/view.php?pg=faq&cmd=category&id=67 which told me everything I needed to know.
Click to expand...
i think im going to go with a s&p 100x. My room is 35 cubic feet, and with a scrubber that should be enough to ventilate the air. Also, the basement air is pretty cool, so i figure it will be enough to keep the hps in its place.
 
Heads Up

Heads Up

Well-Known Member
Will5437 said:
Hello
I am running a 4 ft by 2 ft by 5 ft
I was wondering what kind of fan do I need to exhaust the air, as well as pull it through the inline filter.
What is the cheapest fan that will get the job done?
Click to expand...

You have forty cubic feet..4x2x5, equals forty. Now you divide by five, for the amount of air you need to exchange within five minutes, you get eight cubic feet of air you need to move every five minutes. I think a six inch fan is overkill. A four inch fan will do you just fine, generally they move around 170 cubic feet a minute. Don't waste your money on a six inch fan.
 
Hairy Bob

Hairy Bob

Well-Known Member
Heads Up said:
You have forty cubic feet..4x2x5, equals forty. Now you divide by five, for the amount of air you need to exchange within five minutes, you get eight cubic feet of air you need to move every five minutes. I think a six inch fan is overkill. A four inch fan will do you just fine, generally they move around 170 cubic feet a minute. Don't waste your money on a six inch fan.
Click to expand...
Did you not read the post where he said there was a 400w hps in that space? You vent the room every five minutes if your using fluoros, if using hid then you should have the capacity to vent the room 2-5 times a minute, so up to 200cfm, +50 for the ductwork and filter.
I assume the fan he's talking about getting is something like this http://www.kitchensource.com/bathroom-fans/sl-pv-b.htm and yes, 4" will be fine, assuming the ambient temps aren't high.
 
tea tree

tea tree

Well-Known Member
There is something that never gets any attention on this site tho! Rofl. I was surprised and at first did not care. Lol, then I looked at my fan and dont want to buy a new one soon.

Negative pressure makes a lot of work for the fan. A lot. I read this is the garden magazine "Urban Gardens". They say that this is so and recomend having an intake fan for this reason. I have a pittance of an intake and still have negative pressure. But I am hoping that some work is reduced. It is not completely negative and mostly it is because I use a tent and the walls "suck" in with the appropriate speed exhaust. I use a cheap inline duct booster. It is on its last leg. Lasted 6 months from HTG. But it is an intake. Also some cracks at my tent doors. Let maybe an in. lol. I use an eight inch valueline 800 "true" cfm for outake on that tent, that is for my 600 watt. Also, for my veg, I use a 400 and a six inch outake and I love it. I need no intake as I leave the door open 24/7 and use it to light the room too. Have a portable swamp cooler at the opening. Dont buy one of those. What a freakish waste. Gambling, lol. I hate summer.

IDK, take all this fine. A new fan a few years is prob what we look at.

By the way try googling magazines like "Maximum Yeild" and "Urban Gardener" they are an awesome read.

Thanks for that rep+ back at you.
 
Hairy Bob

Hairy Bob

Well-Known Member
I'm sorry tea tree, but negative pressure doesn't make fans work harder. It makes the air slightly thinner, and so the air creates slightly less resistance on the fan blades. If the passive intake is almost the same size as the exhaust fan, then the air should have no more resistance moving from inside the room out as it does getting from one end of the room to the other.
If the intake is smaller than the exhaust then you are creating more negative pressure than simply having a passive intake, think about it! If you have a fan that blows in say half of what the exhaust is blowing out, then the lower pressure inside the room will cause the air to try to rush in, but it will be slowed by the poxy little fan in the way!
 
tea tree

tea tree

Well-Known Member
Hairy Bob said:
I'm sorry tea tree, but negative pressure doesn't make fans work harder. It makes the air slightly thinner, and so the air creates slightly less resistance on the fan blades. If the passive intake is almost the same size as the exhaust fan, then the air should have no more resistance moving from inside the room out as it does getting from one end of the room to the other.
If the intake is smaller than the exhaust then you are creating more negative pressure than simply having a passive intake, think about it! If you have a fan that blows in say half of what the exhaust is blowing out, then the lower pressure inside the room will cause the air to try to rush in, but it will be slowed by the poxy little fan in the way!
Click to expand...

I dont know dude. I am a little stoned. But I read this in a fairly well organised and put out glossy magazine called "urban gardens". Think about it like this. There is only so much air that can get in and if the pressure is negative then it is indeed less than what the fan can pull. The motor is literally straining to get enough air, like sucking your hand. It makes sense. Really we dont need the extreme negative pressure that people sound like. I have a lot so I recently got a speed control. Just slight pressure keeps the smell. It is the heat of the light I worry about. When that is under control then I dont worry. In winter I kept it off for periods. A speed control on a thermostat (next) is the dream. But hey dude I am not tooling out on this concept like a led debate or something so I am in no big way all over this. I mean this is just me and a fan not a lab. :)
 
Hairy Bob

Hairy Bob

Well-Known Member
I agree that the fan won't be able to move as much air if you have a lot of negative pressure, but if there is a passive intake which allows air to flow in freely, you will only have slight negative pressure, which we agree is ok.
The best an intake fan can do is waste electricity. There is plenty in the faq about this, https://www.rollitup.org/view.php?pg=faq&cmd=article&id=229 https://www.rollitup.org/view.php?pg=faq&cmd=article&id=583
The second one mentions that active intake is beneficial in large rooms, but doesn't give a definition of a large room or explain why.
 
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