The Never Exhausted Debate About Computer Air Exhaust

MERRICKMERRICK In the studio or on a stage
edited September 2004 in Hardware
One of the biggest debates in the discussion of computers is cooling. There are as many different philosophies as there are people. In my experience I have found that air intake fans in a computer rig are actually counter productive. This was first brought to my attention at the AMD website in their .pdf on cooling entitled: "AMD Athlon™ System Cooling Guidelines"

http://www.amd.com/us-en/Processors...39_2983,00.html

http://www.amd.com/us-en/assets/con...oling_guide.pdf

“8. A front cooling fan does not seem to be essential. In fact, in some extreme situations, testing showed these fans to be recalculating hot air rather than introducing cool air.”

I tried this and sure enough I brought the CPU temp down 1 degree C. I spoke with an associate who worked for years on hi tech military electronic systems and he confirmed that military cooling systems are always exclusively exhaustive.
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Comments

  • ThraxThrax 🐌 Austin, TX Icrontian
    edited June 2003
    Yep. I run all my fans on exhale. Dust be damned.

    Better temperatures than 2 exhaust, 2 intake.
  • dodododo Landisville, PA
    edited June 2003
    It seems the major reason for intake fans is to introduce outside (typically cooler) air directly onto the main heat producing components of the board (cpu, vc, hdd, etc). In the case of a side intake fan that blows fresh air on the cpu, the temperature differences are certainly lower with that fan blowing in.

    ~dodo
  • tychotycho Santa Barbara, California!
    edited June 2003
    For my rig, I have a bank of three small fans in one of my CD bays and i find that without them my CPU temp will be about 1-2 degrees higher... but i also know that my case has horrible airflow and nearly no space for naturally air intake... just my experience
  • FudgePackerFudgePacker
    edited June 2003
    I run all 4 of my systems without intake fans. The exhaust fans pull all the air they need. It's also quieter without the additional noise from intake fans.
  • ClutchClutch North Carolina New
    edited June 2003
    Interesting guys. In my main rig, I have one 80mm intake fan and 2 80mm exhaust fans, along with the psu fan. I did have a side intake also, but once I cut out my window, it eliminated that. On my next rig, I am going to try the no intake, only exahust method to see how things stack up.
  • MERRICKMERRICK In the studio or on a stage
    edited June 2003
    I would propose that people using intakes take a temp reading and then try all exhaust. You'd have to do it within a reasonable time frame since outside room temperature makes a difference. Surprisingly I found on my rig that taking the roof off did not change the temp (you'd think it would with hot air rising). One mod that was posted on Icrontic mentioned someone cutting a hole in the case right behind the CPU connection to the MB and putting a small exhaust fan for the REAR of the CPU. They said that there was a 2 degree (?) improvement. Anyone try that?
  • mmonninmmonnin Centreville, VA
    edited June 2003
    I have one side-intake and 2 rear exhaust plus PSU.

    I thought about adding a front fan.
  • ClutchClutch North Carolina New
    edited June 2003
    MERRICK said
    One mod that was posted on Icrontic mentioned someone cutting a hole in the case right behind the CPU connection to the MB and putting a small exhaust fan for the REAR of the CPU. They said that there was a 2 degree (?) improvement. Anyone try that?


    I don't recall seeing that, sounds interesting though. The hole behind the motherboard tray right?
  • MERRICKMERRICK In the studio or on a stage
    edited June 2003
    Another sad reminder of the "lost" Icrontic archives :rolleyes: but yes the original poster had made the hole in the case right behind the motherboard tray. Makes sense. There must be a bitchin' amount of heat back there!
  • leishi85leishi85 Grand Rapids, MI Icrontian
    edited June 2003
    just to throw in some info

    after reading this thread, i tried to put all my fans on my rig to exhaust, and it brought my system and CPU up by like 2C,

    my setup is 2 80mm side intake, and one rear top exhaust, and one exhaust on the PSU.
  • Omega65Omega65 Philadelphia, Pa
    edited June 2003
    Thrax said
    Yep. I run all my fans on exhale. Dust be damned.

    Better temperatures than 2 exhaust, 2 intake.

    Dust be damned is right. I just cleaned a dust carpet out of one of my computers......:aol:

    And I was wondering why it was crashing :shakehead
  • MERRICKMERRICK In the studio or on a stage
    edited June 2003
    All I can say in my defense is that my 'puter I refer to has:

    Case: Full Tower w Leadman/400W PSU

    1]CPU Cooler: Swiftech MC462w/Delta 80mm fan

    2] Lian LI MF-699 mini 3 fan Hard drive coolers on all 5 HD's (fans modified for exhaust)

    3] (1) 90mm rear exhaust fan

    4](1) 80mm rear exhaust fan.

    No intake fans.

    I've actually seen it fly up a few inches lol. I'm a bit of a cooling freak.

    But I respect anyone who disagrees with me. BTW I have one of those neat little cheap mini vacs that I don't use. Did I mention I'm researching my next rig. "Why clean the house when ya can move out?"
  • GargGarg Purveyor of Lincoln Nightmares Icrontian
    edited June 2003
    Do you think the hard drives near the front of the case would still be properly cooled just by the air pulled by the exhaust fans? I have my front fan on (Sunon 120mm) to keep my four hard drives from glowing red :).

    Edit -> And when you all say all exhaust, is that only the rear fans and perhaps a blowhole, or do you also have a front fan on exhaust? And if so, where is it sucking in the air? Some cases have ventilated side panels that would be good for an all-exhaust application, but my case doesn't. Damned Noblesse. Looks sexy, but impractical as hell. :banghead:
  • panzerkwpanzerkw New York City
    edited June 2003
    The one intake fan I have is for blowing air right over the hard drives.
  • dodododo Landisville, PA
    edited June 2003
    panzerkw said
    The one intake fan I have is for blowing air right over the hard drives.

    Same with me....I wonder if this is why some people get higher CPU temps when using an intake fan, the air is heater over the hard drives. Of course, this intake fan probably cools the hard disks better, so its a tradeoff i guess. I personally would stick with a front intake fan over the hard disks and let my CPU temps raise 1C. I dont think an exhaust fan would cool the hard disks properly. Think about it, do you have your CPU fan blowing out?

    ~dodo
  • panzerkwpanzerkw New York City
    edited June 2003
    I have mine blowing air downard into the heatsink.

    Way I figure it, warm air rises, and the exhaust fans are up high. So whatever warm air the hard drives and CPU make will eventually be sucked out as it rises. The intake is down near the floor where the air is cooler. But the difference it makes is probably negligble.
  • profdlpprofdlp The Holy City Of Westlake, Ohio
    edited June 2003
    One thing I have found during my personal adventures in cooling is that you can't make a blanket statement to cover every situation.

    There is such a variety of cases out there that what is terrific for one might be awful for another.

    The one constant I have found is that an intake fan on the side of the case blowing directly onto the CPU/Video Card area is a good idea, provided your exhaust fans are up to snuff.

    My main rig is a full tower (generic) with gobs of places pre-drilled for installing fans. I went on a fan binge a few years back and at one point had 16 fans going! (This included two hard drive coolers which had 3 fans each, a bay cooler with 2 fans, as well as the chipset, cpu and ps fans, a slot cooler fan, twin exhaust fans on the back, an intake fan on the front, and the side fan blowing onto the cpu).

    With the exception of the mandatory fans (cpu, etc) I found that the side fan did more good than all of the rest of them put together (and I tried many, many combinations).


    Prof

    PS: My side fan is a 120V 5" fan made by a German company - it really moves the air!):cool:
  • ClutchClutch North Carolina New
    edited June 2003
    Gargoyle said
    And when you all say all exhaust, is that only the rear fans and perhaps a blowhole, or do you also have a front fan on exhaust?


    Rear fans, blow hole, and a side fan if any. I would think it would be to impractical to have a front exhaust fan. Although air does get inside your case in the smallest cracks possible, it still would be the same.

    I myself would trade 1c for my hard drives to be cooled down, especially if I had over 2 hdd's.
  • MERRICKMERRICK In the studio or on a stage
    edited June 2003
    One thing I have found during my personal adventures in cooling is that you can't make a blanket statement to cover every situation.

    That's the truth. the particular case of my case (pun) is that it came with many vents as well as predrilled fan holes. I feel the vacume created by my exhuast system has plenty of free air inlet oppertunity.

    On the subject of the exhaust hard drive coolers: My hard drives (7200rpms) are "stacked" one over the other 5 high in the front bays. Now since heat rises, that is one hot totem pole. But the moment heat disapates off each individual hard drive it is whisked away and out the case. This minimizes the upper HD's catching the heat from the lower HDs. I had to reverse the mini Lian-Li fans to do this. I honestly can' see how making these fans intake would be better. It would be blowing that hot air into the case.

    I did debate making a blow hole but I first removed the top of the case and took temps. there was no change:scratch: I couldn't believe it but I reckon it was because of the fact that I have so many fans and it is a full tower with many upper rear vents. A smaller case would probably yeild different resultd (?).


    I don't have the typical low front intake fan or any fan their for that matter. I allow those vents to be for intake.

    One thing I'll change on my next rig: I have a single fan PSU. (yeah I know). I'll go for the extra bucks next time and get a unit that has an internal intake. :cool:
  • MarkTAWMarkTAW Brooklyn, NY
    edited June 2003
    Prof - I agree, if your side fan aims directly at your CPU, getting more air to blow directly over that thing may be a good idea. From behind as well.

    I have an interesting (?), off-topic anecdote here.

    I've always been interested in air... We need it to breath, yet so many of us close all our doors and windows for much of the year.

    As I kid, I had this very powerful, all-metal window fan that was probably outlawed when someone got their finger chopped off in one. I'd stick it in the window and within moments the room would cool off... I've never had another fan like it.

    So as a kid, I experimented with it (and I still have all my fingers). I stuck it in the window and put towels in the doorway and tried to experience the changes in atmospheric pressure. Well, I can tell you first hand - you can feel it, and it does have an effect on you.

    Sticking the fan on exhaust, I felt like I was in the mountains. I'd get a little light headed and noticed things more, or like on a cold winter morning. When it was on intake, the atmosphere got a little more oppressive, and my mood showed it as well.

    I know you think I'm crazy or on drugs, but something happened today to make me think otherwise... I was blowing air into the apartment to get it to cool off, but the air outside was hot and sticky, so I flipped the (cheap plastic low power) fan around in the window and the moment I did it, the cats started running around chasing each other. Now, I think they hunt at dawn or dusk or something, and dawn and dusk are often accompanied by changes in atmospheric pressure. Could this change have told them that it was time to hunt? I think so. I might try it again to rule out concidence.

    Back on topic, I'd be interested in seeing some stats here ont he effect of a vacuum on case tempreture. If anyone has a barometer that can be read from outside the computer, something to insulate with (tape or something) to prevent air from getting in and some powerful comptur fans, I think it would be fun to see what effect a bit of a vacuum has on the temperature inside the case and on the CPU. I guess the barometer isn't completely necessary, but it adds some extra numbers to back up any other evidence.

    Is anyone up for the challenge?
  • CammanCamman NEW! England Icrontian
    edited October 2003
    old topic I see, but I figured I'd hit the ol' Search button before posting a new one, maybe one of you can answer me this question.

    I was thinking about installing a blow hole in my case to exhaust heat, but, I've been told by someone that blow holes can actually destroy PSU's by not letting the PSU fan pull the hot air out, so the blow hole pulls all the hot air back over the components inside of it, is this true?
  • Al_CapownAl_Capown Indiana
    edited October 2003
    My Thoughts:
    If that was true why woudl lian li and coolermaster install blowholes on their cases?

    From my experience, my blowhole has not killed my psu, yet...

    If i was you i'd install a side intake near the cpu socket. Be sure it pushes plenty of air. It would cool down the cpu considerably.
  • TheLostSwedeTheLostSwede Trondheim, Norway Icrontian
    edited October 2003
    ALL air that is inside the case is hotter than ambient or room temps, heat rises and to duct the warm air out is a great advice. I can´t understand why this would kill a psu though, it should be the opposite. It will still pull the air out, but the air might be cooler which would be concidered a plus. To reach good or great temps with blowholes/ducting, off course you need an intake of fresh air, and the most effective place to have that is at the front, low front the best.
  • SimGuySimGuy Ottawa, Canada
    edited October 2003
    Here's a question about air flow for all the Antec/Chieftec/Chenming SX1080 users out there.

    Everyone knows the came I'm talking about and it has 5 fans: 2 80mm intakes stacked vertically in the front of the case. The Antec SX1080 has a dust filter to prevent those awful dustbunnies from being sucked in.

    Installed in the rear are 2 80mm vertically-stacked exhaust fans.

    Installed in the left-hand side panel is 1 80mm.

    I picked up a couple of Panaflo 120mm U1A 115 CFM case fans and plan on mounting them horizontally along the base of the left-hand side panel, eliminating the 80mm intake fan located there.

    AFAIK, you are supposed to balance exhaust with intake. The location of the 2 new 120mm Panaflo's will be directly over the expansion cards and just lower than the CPU.

    Here's the question: Would having the 4 remaining 80mm case fans work as exhaust fans only instead of 2 exhaust, 2 intake fans work better with the dual 120mm's intaking? Is it wise to have that much intake pressure? Thoughts?
  • CammanCamman NEW! England Icrontian
    edited October 2003
    sounds good fellas, thanks for the responses.

    A long time ago I got this 120mm monster from "3dfxcool.com" , cant remember the name of the site now, like 2coolcpu or osmething? but anyway, I think I might try that for a side intake.
  • Mt_GoatMt_Goat Head Cheezy Knob Pflugerville (north of Austin) Icrontian
    edited October 2003
    What about putting all case fans to exhaust as mentioned but adding a "cold air induction" for the CPU so all the cool incoming air goes over the HS. In addition I would conclude that having a 120mm fan for the intake and gradually tapering down the tunnel to the size of the fan on the HS so as to increase velocity of the incoming air and there fore cooling it slightly.
  • LeonardoLeonardo Wake up and smell the glaciers Eagle River, Alaska Icrontian
    edited October 2003
    Principle. It's all about physics. The more air, up to a point, that you can pass over a heated solid object, the more heat will be washed away. Assuming you have a case that has zero drag at the intakes - zero obstructions, then yes, it would seem logical that an intake fan would not be necessary. Due to most case designs, air exhausts with much less restriction than air can passively enter the front. Without the front case fan(s) most of our computers will have negative air pressure relative to the environment outside the case. I don't have any data, but it just seems like even a slight vacuum would allow for pockets of hot air in the case that wouldn't get flushed out.

    Again, not talking about a rule here, but a principle. As a couple other posters said, I think you just have to experiment with every case setup. I've got homemade airfilters at the front of both of my home computers. Without the air intake fans, case and CPU temps are elevated.
  • danball1976danball1976 Wichita Falls, TX
    edited October 2003
    Seeing as how I see a lot of LRU's on the B-52, other than the air duct cooling system thats on the B-52 for most of the larger LRU's, most smaller ones have a fan the pulls air out of the LRU.
  • Geeky1Geeky1 University of the Pacific (Stockton, CA, USA)
    edited October 2003
    Actually, the G5's case is almost ideal from an airflow standpoint. I've been trying to design something somewhat similar for an ATX computer... If you were to set up a computer case with several large fans blowing across the motherboard and CPU at a 90* angle (e.g. a blowhole) and had the rest of the case open enough for the air to escape, you could keep the MB and cards near room temperature. I've run boards outside of the case, and if you put one or two of those rotron 6.75" fans blowing across the board, everything drops to a few degrees above ambient, except for the CPU, chipset, and video card (although if you have a really good cooling setup on them, they'll drop a great deal too.

    I just haven't found a design I'm happy with yet...
  • Straight_ManStraight_Man Geeky, in my own way Naples, FL Icrontian
    edited October 2003
    Typically, the traditional case flow is from low in front to high in back.

    Where you have a hyper hot CPU and the best heatsink and thrmal compund you can get (Arctic Silver Ceramique after about 200 hours of runtime comes to mind), and you still have an overheat problem, I woudl try this:

    Put an extra or higher CFM back exit fan, and move the case so it has 8-10 inches between it back and the wall so the heat can rise up and flow away from computer.

    Then, if still having problems, put a blowhole fan of about 20-25 CFM aligned with CPU cooler to vent air from the CPU fan exhaust.

    If you still have issues, check your voltages real versus right with a voltage\heat monitor software and see if the CPU is misvoltaged or the 3.3 or 5 volts lines are misvoltaged. If they are test your surge strip and the wall outlet. running too much juice through CPU will heat it up big time, and PSUs can vary high or low, so sometimes you have to compensate with the BIOS settign to allow for a cronic under or overvoltage from the wall outlet or give the box the present of a UPS that will chop to batery at +\- 8% or so. If a UPS is present and you still get lots of misvoltaging, probably time for anew bigger PSU.

    The other reason for a blowhole is sometimes a cheap PSU mfr will make it vent INTO the case, or misassmble the fanning and get a fan blowing into case, and in that case (especially with the nice insulation of a plastic or polycarbonate window compared to a heat-conductive metal case side) a low to mid volume outward venting blowhole fan is nice to both make up for the extra heat holding of a plastic window AND to help compensate where some idiot has a computr that blows heat from PSU right on CPU heatsink instead of sucking air AWAY from heatsink.

    NOTE, you do not want a high volume blowhole fan, instead use high volume exhaust fans in back-- otherwise, the effects of the exhaust fan in blowhole on side interfere with the normal front/low to back/high airflow. blowhole should only supplement if NEEDED.

    John.
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