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Thread: My grow box fans

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    New Member josh1987's Avatar
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    My grow box fans

    So i have a grow box of 5'x4'x5'. i want to use computer fans installed into the walls. how many do you think i should use? i looked at strats and he used very little and it became an issue. so i thought to use like 3 time the amount. but is that over kill?

  2. #2
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    Re: My grow box fans

    Buy a proper fan.Those comp fans are BS.
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  3. #3
    420 Member Lil Neutrino's Avatar
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    Re: My grow box fans

    I have to disagree...computer fans are not BS, they are just not suited to larger grow rooms. You would need too many to move the proper amount of air and would take up half a wall.

    Josh...your grow room is 100ft^3, general rule-of-thumb is to move 3-5 times the volume of air in your room per minute.

    edit: I got that mixed up...and I was sober lol. You want to exchange the air volume in your grow space every few minutes...3-5 minutes is a general rule-of-thumb. Sorry for any confusion :(

    See candyman's post here:
    http://www.420magazine.com/forums/ca...aust-size.html

    Ignore the parts in bold as they are incorrect...thanks.
    That means you would need to have enough fans that could move 300-500cfm. Most computer fans will move no more than 50-60cfm (for the 120mm pushing around 1500RPM) and the ratings on the specs are often a tad inflated. If you found a 50cfm computer fan you would need at least six of them to get minimal air flow and even then your interior temps may stay too high. You can get cheap fans but they're a bit noisy and prone to breaking or you can spend $10-15 per fan and get quieter and more reliable perfomance.

    edit: I wish I could say I was smoking something when I posted the above but alas I can not :( Since my other statement was incorrect this one is too. You could use a 50CFM PC fan and meet the rule-of-thumb specs. You may need more depending on how hot it gets in the grow room...the faster it exchanges the hot with the cool air the lower your temps will be. Naturally though you can't cool it down any farther than ambient air temperature. My test box right now hovers about 3-7F above ambient which I think is good, better than the 15-17F higher before I added a second fan!

    You would need quite the large hole cut out of the wall for the exhaust and a slightly larger one in another wall for the intake. Now you've got the problem of keeping the light from escaping or more importantly getting in during flowering. Not to mention if you plan on using a carbon scrubber you will need some fans with some balls (static pressure) to push the air through the scrubber. Computer fans aren't really designed to deal with things like that as they are meant to simply pull air through a computer case and over a few cards sticking out of the motherboard. I'm not saying they won't work just that other fans are probably a better choice for that size space. Again, see the thread I linked to.

    If you're doing a very small grow PC fans would work fine because you don't need as many of them and the scrubber, if used, will be smaller. Trying to run a bunch of PC fans in to one duct and in to the scrubber would be a PITA.

    Then there's the matter of powering PC fans as they run on 12VDC...you'll either need a computer PSU (might be lucky enough to have one laying around) or a converter to go from 120VAC to 12VDC. There are some of these that you can buy and plug in to your outlet that are ready for use or you may have a phone charger or something that puts out 12VDC that you can cut the end off of and wire to the fans. Either way you'll have to do some electrical splicing as the PC fans have special plugs on them...unless you use a computer PSU and in that case you'll need to mount it inside the enclosure (more heat) or somewhere outside but concealed so as not to draw attention (may or may not be a priority depending on where you're doing this at).
    Last edited by Lil Neutrino; 06-01-2009 at 05:43 PM. Reason: Made some serious mistakes...corrected them

  4. #4
    420 Member Lil Neutrino's Avatar
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    Re: My grow box fans

    bump so Josh knows I changed my answer in case he already looked at it...I don't think emails are sent out when someone edits a post in a thread. Sorry Josh!

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    Re: My grow box fans

    You'r right,the're not bs,you just need 10 of them to provide the proper amount of air flow to your room.Oh,& since most of those comp fans run on dc not ac current,you're going to need a transformer/ power supply to change ac to dc & wire all that stuff up,are you an electrician Josh? Me,I like to just plug & play,good ole 120 vac.
    p.s. not trying to be an ass lil n,but you wrote a 350 word post that explained exactly what I said in my first reply to Josh,for a room the size of his, the comp fans aint going to cut it.
    Last edited by Kash Krop; 06-01-2009 at 09:13 PM. Reason: ps

  6. #6
    420 Member Lil Neutrino's Avatar
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    Re: My grow box fans

    No offense taken Typing longer replies is nothing to me...that took maybe 3 minutes to type up. I've always been a fan of offering explanations instead of one line replies that can leave the OP coming back with more questions that could have been answered in the initial reply What do you care if I type a long but educational reply so that others who read this thread understand exactly why they may not be a good choice in some situations?

    Your statement that the PC fans were BS was a very broad, blanket statement...I was clarifying what you said as you pointed out. I'm not trying to be an ass either but simple replies such as yours that do not tell the whole story and can mislead people bother me to an extent. I know some people type slow but at least take the time to explain yourself (adding, "...in a room that size." wouldn't have taken long). Sorry if I sound like I'm busting your chops...

    As for wiring them up it does not take a genius, as a matter of fact I've seen some downright stupid people accomplish far more complicated wiring. Some people have computer power supplies sitting around especially if they build their own computers. Cutting off a plug and connecting TWO wires is not rocket science, no harder than wiring a car battery, but may require some basic tools that not everyone has (wire cutters/strippers and something to splice the wires together). One is positive, the other is negative...if it doesn't work wired one way just reverse the wires.

    He will not need a boat load of comp fans to move the proper amount of air. Computer fans can easily be found that will move 60-70CFM...that's about 200ft^3 in three minutes and 300ft^3 in five. That meets the general rule-of-thumb requirements, right? And that's with ONE fan and no louder than a bathroom ventilation fan or whatever else you can find, actually probably quieter unless you doubled up and went with two to get 600ft^3 of air movement in five minutes. The major question is what kind of light is he using in there; if it's some really hot lamps then by the time he gets enough comp fans to allow proper air cooling/exchange he'd have been better off with a different kind of fan that offers more CFM with fewer cut-outs.

    I don't know what kind of comp fans you have experience with but there are comp fans that will push WELL over 100CFM but at a high RPM. Here's some 120mm fans that are all rated over 80CFM...the SilenX brand listed in this Newegg link is well-liked amongst some computer builders as well as Scythe and others:

    Newegg.com - Computer Hardware,Fans & Heatsinks,Case Fans,Case Fan,120mm,>80 CFM,

    Larger diameter fans are also available but the problem I find with computer fans is that many of them have LED's built in...not something most people in this situation want but there are plenty without LED's too.
    Last edited by Lil Neutrino; 06-01-2009 at 10:51 PM. Reason: car battery example

  7. #7
    New Member josh1987's Avatar
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    Re: My grow box fans

    so i kind of had a new idea. i will use 3 or 4 8 inch fans to bring new air in and push air out into carbon filters to reduce smell. 1 for in and 1 for out. the other 2 will be used to circulate the air. each are 10 volts so i save on over amping the system.

    The link to the fans

  8. #8
    420 Member Lil Neutrino's Avatar
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    Re: My grow box fans

    I have one of those fans...it's dying though, well, it's not mine exactly. I had a new one and when a friend came over for refuge during a hurricane he brought his which is the same. When he left he took my brand new one and left me his old, dusty one lol, didn't notice for a few days and didn't really care until it started to make noise recently and takes forever to get up to speed. I bet he's enjoying my new one though :D

    How do you plan on rigging these up for intake and exhausts? Dismantle the stands and caulk them in to the walls?

  9. #9
    New Member josh1987's Avatar
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    Re: My grow box fans

    Quote Originally Posted by Lil Neutrino View Post
    I have one of those fans...it's dying though, well, it's not mine exactly. I had a new one and when a friend came over for refuge during a hurricane he brought his which is the same. When he left he took my brand new one and left me his old, dusty one lol, didn't notice for a few days and didn't really care until it started to make noise recently and takes forever to get up to speed. I bet he's enjoying my new one though :D

    How do you plan on rigging these up for intake and exhausts? Dismantle the stands and caulk them in to the walls?
    Not exactly sure yet. i found some expanders/reducers that fit wonderfully at home depot. i was going to cut the holes to fit the e/r in the walls of the box and some how hang them with something. maybe ropes. any ideas are greatly appreciative.

    those fans that i wanted to use was at a bar i worked at. that was nearly 2 years ago and they still use them and never cleaned. i plan on after every grow to clean my fans with compressed air and if need be cleaners of some kind. i plan on spending about a $1000+/- on this room. <thank you exxon>

  10. #10
    New Member josh1987's Avatar
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    Re: My grow box fans

    room actually got smaller. 4x4x5. mdf only comes in 4x8 sheets

  11. #11
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    Re: My grow box fans

    I got some 109 CFM German-made computer fans that work really well for my 120cubicft flowering room. Only had to use one. They work with standard 120v 20amp power so no crazy power source required. Cost about $35 each. All metal casing and smooth. Not too noisy either, but proper ventilation of an enclosed grow room will never be silent. You can minimize it through mounting buffering materials in between the fan and the wall. Cardboard actually works rather well. They are Pabst-Motoren 4600xp (120mm 20W 50dB).
    As for blocking light, if you can build a birdhouse you can build a light blocking box. It's simply a box that routes air through a passage that turns corners enough that light cannot pass. Air goes up through the bottom, around a 180deg corner, around another 180deg corner, then out the side, through the hole in the wall and through the fan. I put a piece of air filter material on the bottom's intake hole to keep the dust out.
    Hope this helps....
    growtender