View Full Version : Direction of case fan?

10th June 1999, 02:26
I have(since yesterday) a new Gigabyte motherboard,P2 400Mhz(thanks to Jammrock for rekomendig STEP),128Mb PC133 RAM, new case and finaly a CASE FAN. Now to my question, should the case fan blow air in or out?

10th June 1999, 02:56
Hi Erich,

Hvordan går det? Your case fan should (I assume it is the fan on the bottom front of your computer) should be blowing air into the case. The fan in your power supply should be blowing the air out of the case. Simple physics, cold air sinks (so to say) and hot air rises. The case fan sucks in cool air into the case. The hot air in the case rises to the top, the power supply fan blows the hot air out.


10th June 1999, 06:17
Det går ganska bra. I still have one litle problem though, it occures when I overklock my P2 to 496Mhz. When I for example play a game the computer stops for some seconds and then continues(it dosenīt crash). And my harddisc have also been erased twice. The latest haddisc problem started when I booted up, it seemd to start as normal but I got a error message when I got in to windows saying that the registry had been damaged and I needed to restart to fix it. When my computer restarted I ended up in the menu which you can get if you hit F8(donīt know its name in english). And it said that I needed to start in dos mode and run scanreg. When config.sys and autoexec.bat was executed I got some alarming error messages. Canīt find the file(or similar) on all lines in config.sys and autoexec.bat and i needed to format my harddisc to get everything to work again, my harddisc was erased after some hours of use and not the first time I started at 496Mhz. The only thing which is realy warm is my Mill G200 my P2 is not warm at all. One good thing is that my computer can start at
533(4*133) but it locks up when I see the desktop.

My specs:
P2 400, 128Mb PC133 RAM, Millenium G200(4,51,bios 2.3),2.6GB Fujitsu HD, Sound Blaster AWE 32, TEAC 32x CD-ROM,Gigabyte GA-6BXE motherboard

10th June 1999, 08:16
I have had same problem. You don't by any chance have a Voodoo 2 card in your computer? I downloaded the Quake 3 compatible Voodoo 2 drivers for my computer and everytime I install them my registry gets fried and I have to format my hard drive. Either those drivers are really bad, or there is a virus in them. I highly doubt that overclocking the CPU would cause any problems with the hard drive, though. The only possible way that this could happen is if overclocking the bus caues the hard drive timing to go bad and cause irregular read/writes. I highly doubt that is the problem, I have never heard of anyone complaining about their hard drive while overclocking. I didn't have any problem runing at 75 MHz bus (37 MHZ PCI bus) until I loaded those bad drivers. I would suggest formatting and rebuilding the partition with known good drivers and programs and keep an updated virus scanner running.


10th June 1999, 21:15
I had similar registry-whining symptoms after replacing my K6-2/300 with a K6-3/400 and Quantum 3.2 Gb IDE HD with a IBM 9.1 Gb UW-SCSI HD. The registry got mixed up, had to re-install most of software. In my case the problem was probably temperature-affiliated, the HD got too hot if case was shut. With case open everything runs fine. I'd suggest you'd check this - one 80mm fan sucking in and one out doesn't seem to be enough http://forums.gagames.com/forums/frown.gif
Specs: AMD K6-3/400, FIC VA-503+, 128Mb PC-100 SDRAM, G200, IBM UltraStar 9ES 9.1 Gb


[This message has been edited by Juza (edited 06-11-99).]

11th June 1999, 00:24
You could also try turning off UDMA and even putting your HDD down to mode 3. Most hard drives (fujitsu included) aren't fond of the high bus speed.


Intel Inside and Currently running PD 5.20.xx and BIOS 2.5xx on not that bad a PC with all sorts of bits n bobs in it helping to find ET calling home... :)

ICQ: 29468849

11th June 1999, 02:21
I second SteveC's opinion, it is almost a must to take the HD off UDMA. I had very similar problems with my PII 400 O/Ced at a 112MHz bus speed. All the problems went away when I turned UDMA to OFF. I have a question for all of you, though. I am interested in putting a new heat sink/fan setup on my PII. How do I remove the heatsink/fan that came preinstalled on the processor? There are two hexagonal screws that I can see in the two holes on the fan/hs on there now. I have some thermal grease and I am interested in getting a three fan/hs setup. Does anyone know of a good fan combo that I can purchase out of the US?


Asus P2B-F, 400MHZ Pentium II (O/C to 480!!), 128MB Micron PC133, Maxtor 4GB, SB AWE 32, Sony Trinitron 17", Old Matrox Video Card

12th June 1999, 08:24
My problem are solved!!I am now running at 533Mhz(133*4)PCI at 33Mhz. But I do have one more question(perhaps two). If I want to stress my system to the max. Is running the massive1 and crusher demo in a loop a good idea or is something els better? If I want my system stable at 496Mhz, setting my HD to mode 3 is a must(have been testing all day). But how much does this effect prefomance?

Jammrock. I donīt have any Voodoo2 card in my computer. I must say that STEP have done everything they promised.Thanks again!!

16th June 1999, 03:53
A little problem have come up. As long as I donīt close my case my computer is stable as a rock but when you close the case it craches because of to much heat. I still have a case fan in the bottom front of my computer but I have bought two more but where should I place them?

16th June 1999, 06:10

Doh! Uh, well, I could give some suggestions, but there aren't any Radio Shacks in Sweden (not that I am aware of anyway). Basically what you need to do is create a really good airflow system in your case. Depending on how crazy you want to go, and how mechanically gifted you are, will determine what you can do. Basically you need additional fans in the front, to increase the inward airflow. Then you need a fan on top to suck the air out. The best way to get air out of the case is to cut a hole in the top of you case, fasten a fan in the hole that blows the air out of the case, and hook it up the power. There are a lot of things that you can do, but the more fans you have the more power the computer uses and the more noise it makes.


22nd June 1999, 10:02
In response to fan direction,
I believe the previous reader is incorrect.
Intel's ATX case white papers call for the power supply fan to pull air into the case. According to the same specs, the case fan should be blowing air out. This is a reversal of air flow from the AT form factor.
The previous reader's intuition was correct, however. Hot air does rise. Due to simple thermal dynamics, the AT case is really a better design. The reason Intel changed the specs on the fan directions was so that the CPU would get extra air from the power supply fan. The only problem with this is that the power supply, too, gets hot and you end up blowing warm air on the CPU.
The best solution if you are willing to take apart your power supply is to reverse the fan in your supply so that it is pushing air out of the case. This way, you can have the front case fan pull cool air in from outside of the case.

Hope this helps,
Ray Chow

22nd June 1999, 12:41
So basically do what I said you should do in the first place.


22nd June 1999, 17:59
Actually, it is not really the same as what you described. Your description ONLY mentions to mount the case fan so that it pulls air into the case. You incorrectly stated that the power supply fan pushes air into the case (ATX form factor). It does not. It pulls air in. Failing to mention this point is critical as it would be a very bad idea to have the case fan and the power supply fan blow into the case.
The most important thing in case cooling is air flow, not simply blowing air into the case. This can be more detrimental in that such an arrangement would likely result in a so called, "hot spot."
Ceterus paribus in an ATX case, it would be far better to have the case fan push air out of the case than to have it pull air in. One should only mount the case fan to pull if the power supply fan is reversed. Your post fails to mention this critical point.

22nd June 1999, 23:23
I said in my original post, "Your case fan should (I assume it is the fan on the bottom front of your computer) should be blowing air into the case. The fan in your power supply should be blowing the air out of the case." Meaning that the power supply fan should be taking the air out of the case. You said in your last post that I said differently, just would like to clarify a bit.

Jammrock http://forums.gagames.com/forums/wink.gif

Celeron 450 (6 x 75) w/ Step Thermodynamics YUKON cooler, 256 MB PC133 SDRAM, 18 GB WD Expert (7300 RPM), CL Encore 6x DVD w/ Dxr3 decoder, (soon will have) G400 MAX, Sound Blaster Live! (full retail), Cambridge Sound works Desktop Theater 5.1.

23rd June 1999, 07:49
Hello Jammrock,
Please understand that my comments are not meant to attack you, personally. I am just trying to help Erich out with the cooling of his case.
I was just trying to clarify things. Your original post states, "The fan in your power supply should be blowing the air out of the case." This is not really true since the power supply fan is supposed to blow air into the case (I believe there may be a typo in my former post). Again, Intel's designer sheets for the ATX form factor specify this. I agree, though, that it would be BETTER to have the power supply fan pull air out of the case. However, when one first brings an ATX case and power supply home, it should indeed, be pulling air out of the box.
Perhaps I am misunderstanding your prose, but the ATX power supply case "should" definitely NOT be blowing air out of the case (if it is, the polarity of the fan could be reversed and Erich should get it checked out...assuming it is indeed an ATX case...which it should be since it is a P2). What direction the power supply fan should be doing and what would be better are better are two different things.
If Erich has not switched the power supply fan (and does not intend to do so), he should have the case fan (lower front) blow out.

The direction of your fans really depends on many things. If you leave your case the way it is, you should definitely have your case fan blowing air out so that you have air flow. Having the power supply fan and the case fan both blowing in would be a bad idea. A good rule of thumb to follow is to have the same volume of air blowing air in as out.
I will use my box as an example:
P2 450
320 meg RAM
Abit BH-6
Matrox G200
Asus TNT2 Deluxe
Soundblaster Live Value
10 base NIC
Diamond SupraMax
8.4 Gig Fujitsu and 17.3 Gig Fujitsu
Mag DX 700T
Samsung 900 IFT 19"

As you can tell, my box is crammed full and consequently, generates tons of heat. Before cooling, I was running at 48 C. I now run at 34-37 C.
I do have my power supply fan reversed. This is easy to do, but you have to be careful not to get shocked. There's quite a bit of juice stored in that thing. One 8cm case fan blowing in...again, I would not do this unless I had my power supply fan reversed. One PCI slot fan, one 6cm vent fan, one blower on top, and two 4cm fans in one of the 5 1/4 bays (blowing out).

Note that the total area of fans is pretty much the same for in and out.

23rd June 1999, 16:32
Well, I've seen the benchmarks, and there is a significant difference between ->PS->case-> airflow, and ->case->PS->
It is *very* worthwhile to change the direction of the PS fan, if it is indeed working as an intake. I've installed new PS fans before, and it's not at all hard to undo the screws and swap the direction.
If that still doesn't do the trick, I couldn't overclock with the case on, until I added a slot fan. It occupies my highest (heightwise) slot, and blows out even more hot air.
I can't stress enough the need for exhaust fans like this. If there's not hot air being forced out of the case, there's no room for the cold air to be brought in.
Good luck, and happy clocking!


P.S. - A great stress test for the processor is called Prime95, it will suck up every idle clock tick you have. However, it doesn't stress your video setup, so if you're looking to check your heat flow, this may not be enough. However, it's great for burning in a chip http://forums.gagames.com/forums/wink.gif

503+ rev 1.2a, 128MB PC100 RAM, K6-2/350@400,Win98,G200 Millenium (SGRAM)

28th June 1999, 22:01
StingRay69, not all atx cases have atx power supplys. some atx cases have converted at power supply's, that blow air out. to be sure you have a atx p.s. the fan must draw in and the p.s. must suport atx power management comands from the mother board and windows 95/98. i happen to own one real atx case and ps. and two that have converted at supplys.

i spend way too much time and money on my 3 systems.

6th July 1999, 17:49
Well, I know I got here way late, but if anyone's still around looking for cooling options, here's a great "how-I-did-it-myself" article...


check out the whole site; it's really chock full of useful info...

who couldn't even get her K6-333 to run at 350 but wants to try again with a C300 or 366 'till she's saved enough for an Athlon.....

[This message has been edited by motub (edited 07-07-99).]