Adding case fans noob questions

By tunk
Aug 11, 2010
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  1. I know there are so many threads about this but I need quick answers!

    1. I have two big 120 mm fans on the rear of my computer blowing air out of my computer (does that mean those are INTAKE or EXHAUST?), outside of the CPU and GPU fans that's all the fans I have :(

    2. I am adding THREE fans, one on top, one on the bottom, and an expansion slot video card cooling fan. Since the two rear fans are blowing OUT, how should I set the top and bottom fans?

    3. My video card is at the top of the expansion slots, how close to my GPU should I install the video card cooling fan?

    Thanks!
  2. crunchie

    crunchie Malware Helper Posts: 761

    There are different theories regarding positive or negative case pressure.
    My way of thinking is to have a negative pressure in the case so that the cool air will be drawn into the case (the cool air will actually be trying to get in there because of the very slight difference in pressure) and the hot air expelled better.
    Positive pressure imo, will cause the warm air inside to possibly mill around inside the case before being evacuated.
    So, the two fans on the back of your case are exhausting air, creating that negative pressure. I would put the one on the top as an exhaust also, as hot air tends to rise. I would then, if possible, put the other fan at the front of the case as an intake, so that the cooler air is drawn across the motherboard.
    You can also have the one on the bottom as an intake too.
  3. captaincranky

    captaincranky TechSpot Addict Posts: 10,014   +716

    Fans in the front of the case should blow into the case (intake).

    A fan on the side of the case should blow into the case, (intake). The side fan should be turned down somewhat, to avoid impeding the flow of air coming from the front fan(s).

    Fans on the rear of the case should blow out the back of the case, (exhaust).

    A fan on the top of the case should blow out of the case, (exhaust).

    An interesting way to look at it this; both the front and rear fans should be blowing IN THE SAME direction, toward the back of the case.
  4. crunchie

    crunchie Malware Helper Posts: 761

    Thanks for the back up :D
  5. tunk

    tunk Newcomer, in training Topic Starter Posts: 25

    guys...thanks for the response.

    I installed the top fan so it exhausts (blowing out)
    But, I installed the bottom one to exhaust too...will that be ok? If I turn it around and have it intake does it matter that the fan is situated so that it will be blowing directly onto the GPU fan? ( The GTX285 is a HUGE card).
  6. captaincranky

    captaincranky TechSpot Addict Posts: 10,014   +716

    Oh, Before I start; crunchie, you're quite welcome.

    Well, with a bottom fan "exhausting" out the bottom of the case, first, you're trying to reverse the natural flow of hot air rising. Second, since the GPU fan is trying to suck air in at the same time, all you're doing is removing the source of that air, and forcing the GPU fan to find air in a vacuum.

    If you point the bottom fan blowing at the video card, it then creates a high pressure area over the card, and actually starts to work as a "turbocharger", taking some of the load off the GPU fan, and causing it to spin faster.

    So, you can do whatever your heart desires, but someday when I'm rich and famous, and have a case that accepts a bottom fan, I'm going to install it to blow into the case.

    The best way to track your cooling progress / adventures is to open up your hardware monitor, and run a program that uses most or all of the CPU (Spybot SD16 will do this), then light up a cigarette and blow some smoke into the case and watch where it goes.

    In a complicated fan arrangement such as the one you describe, a dedicated fan controller is a necessity. First, to balance the airflow, since you can do as much harm as good letting all the fans run at full blast, and second as a noise control measure, since if you're not gaming, and/or it's a nice cool day, you don't need all that cooling, and it gives you a chance at a little peace and quiet.

    You also have to take into consideration that having a case that has more fan holes than the other guy's, is partly a bunch of marketing BS.
  7. tunk

    tunk Newcomer, in training Topic Starter Posts: 25

    Cranky, thanks for helping out! Lemme describe my case fan situation as quick and painless as possible...view my public profile, threads started, and go to the one with the title "My computer randomly is shutting down" (read my opening post then #16 & #19) and you'll see what exacly is happening!

    My computer area is upstairs and even with central air it is sooo frickin hot up here! I've been blowing a "house" fan on my rig with the side panel off ever since that discussion. I've finally procrastinated enough and now adding the fans and closing the side panel to see if my rig doesn't shut down.

    If that doesn't work Im gonna have to move my computer area to the basement where it's MUCH cooler and/or get a new case with better airflow and/or keep blowing a housefan on my rig!

    BTW, I definetly will switch the bottom fan to intake instead of exhaust!
  8. captaincranky

    captaincranky TechSpot Addict Posts: 10,014   +716

    Exactly, since you have a first floor full of cold, dense, heavy air. Most older HVAC systems are only half a** designed to balance the cooling anyway. You would need really powerful fans in the air return ducts to yank that hot air back down into the basement to be cooled. If the attic isn't adequately insulated, that could add to the problem.
    Now yer talkin'! Computer geeks are supposed to live in the basement anyway, at least until they're thirty five or so...:rolleyes: Just be mindful of the humidity, basements tend to be quite damp.


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