New fan exhale or inhale

By Sab3r
Jun 15, 2005
Topic Status:
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  1. I've seen a thread about whats better, exhaling or inhaling, but I still don't which
    is better.

    Exhaling: if it exhales it'll blow the hot air out but where would cool air come in

    Inhaling: Cool air will get in but where will the hot air go out.

    Now Inhaling will seems better since you'll get cool air in and the hot air will come
    out in the front (I've got this sort of ventilation hole which is used for cd drives....
    works pretty good actually) but Exhaling also sounds good since the hot
    air will come out faster than using a "ventilation hole".

    I haven't bought the fan (fans?) yet, I got two spots for small fans and they
    are only 5 euro's each.
    OR should I set one on exhale and the other on inhale.

    Thanks anyway :wave:
  2. howard_hopkinso

    howard_hopkinso Newcomer, in training Posts: 25,948   +19

    Depending on your case. One on the side blowing in, and one on the back blowing out.

    Just my 2 cents.

    Regards Howard :grinthumb
  3. Sab3r

    Sab3r Newcomer, in training Topic Starter Posts: 72

    thx :approve:

    but I can't really get a fan in the front, only two in the back :( .
    I'll try to give you some more info on which case I got (repeat: i'll try)
  4. howard_hopkinso

    howard_hopkinso Newcomer, in training Posts: 25,948   +19

    I didn`t say the front. I said the side.

    Even if there isn`t a hole in the side of your case, it wouldn`t be that difficult to cut one into it.

    Regards Howard :cool:
  5. Sab3r

    Sab3r Newcomer, in training Topic Starter Posts: 72

    just drill in a hole? :eek:

    thats...... erm, well I don't wanna go that far on modding, maybe i'll do that next
    year when i'm going to build my very first pc.

    anyway is it then worth it to get two fans in the back? and which way should
    they/it blow.
  6. howard_hopkinso

    howard_hopkinso Newcomer, in training Posts: 25,948   +19

    In that case. I`d have them both blowing out. As you say you`ve got a grill at the front of the case for the air intake.


    Regards Howard :grinthumb
  7. Sab3r

    Sab3r Newcomer, in training Topic Starter Posts: 72

    the intake is actually an exhaust if you will ;) , I meant that the hot air escapes
    through it.

    I made a picture of it:
    clicky

    EDIT: I also want to know how to get cold air in the pc when its summer...
  8. Tedster

    Tedster Techspot old timer..... Posts: 10,074   +13

    Generally follow the rules of thermaldynamics and you won't go wrong. Place exhaust fans near the top and rear of the case. Don't have an intake fan right next to an exhaust (like next to the power supply), you'll just create a loop.

    Place intakes near the bottom or to a side.

    If buying a video card, look for one with a fan on it.
    Use rounded cables instead of flat (the circulation is improved inside somewhat.)
  9. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    I'd like to say something about placing exhaust fans fans on top of the case. It didn't work as well as having an inhale fan there (and the numbers to back it) so I'd say it depends on a few things, such as the temperature in the case to start off, and the number, position and direction of the fans you're operating.
  10. tom_pearson

    tom_pearson Newcomer, in training Posts: 103

    Well surely an exhaust fan would be more efficient, as this will not only drag warm air out of the case but will also cause a vacuum effect thus pulling air in regardless of whether there is an intake fan or not. In my case I have about 4 exhaust fans and one intake on the front. I'm not an expert, correct me if I'm wrong!
  11. Mugsy

    Mugsy TechSpot Maniac Posts: 410

    Fan placement

    Just a note.

    When installing a fan that blows inward, *make sure* the fan does not blow on another fan! This will interfere with the second fan (cause drag), preventing it from spinning at full speed (so if you try the "one fan blows in, one blows out" method, make sure they don't line up so one blows on the other).

    I've seen a lot of people make the mistake of installing a fan right on the side of the case that blows down on the motherboard, interfering with the heatsink fan, and end up doing more harm than good.

    My experience has been that fans that blow "out" don't do a damn thing. To create enough of a vacuum to draw out heat, you'd need a fan that sounds like a jet engine inside your PC (personally, I run my PC with one side panel off. It's louder, but gets too hot boxed up).

    This should help you decide on fan direction/placement.
     
  12. tom_pearson

    tom_pearson Newcomer, in training Posts: 103

    but surely with (in my case) 4 exhaust fans. there is bound to be air drawn in through various vents in the case whether there's an "in" fan or not. The amount of air movement is blatently enough to do this?
  13. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    The air movement will not be large enough, ESPECIALLY running the comp with the side panel off. I've run a computer with the side panel off a few years back thinking that'll cool things down, but it did just the opposite, plus tehre's all sorts of radiation coming from inside the computer which the casing is supposed to shield you from. So bottom line is DO NOT RUN THE COMP WITH THE SIDE PANEL OFF.

    Also, in theory if you have enough inhale fans, you don't need an exhale fan. But in theory, compressing air just causes it to heat up. What mean is that theory doesn't always show what will happen in real life (and hence, theory).

    So, my suggestion is, run about equal numbers of inhale and exhale fans. If you want to cool a certain component, have an inhale fan blowing onto that component, and worry about where the hot air goes to later. If it'll mean that you have 5 inhales and no exhales, but since all inhales blow onto something which needs to be cooled (and since its taking air from outside, which is cooler) that particular component will always receive cool air. Which is also the reason why alot of people place those air ducts to their CPUs.

    I've done quite abit of experimenting, and I've posted the temperatures for these experiments on a thread in this forum, but I'll just summarize here. 2 identical comps with just one exhale at the back: 50C (CPU). Add a front inhale fan: 40C. Double the wattage of a PSU exhale fan: 35C. Make your own theories there.

    Another comp with 3 fans, 1x120mm exhale (back), 2x80mm inhale (top and side). Changed the top fan to exhale (cos theoretically hot air rises), and CPU temp goes up 2-3C.

    I don't want to even try running a comp with the side panel off now (unless I'm gonna get a table fan blowing directly in there).

    So 4 exhaust fans? I'll say that there will be cool air going in from various places, but chances are that they're not reaching where they're really needed. Get some fans inhaling to parts where they're needed ASAP.

    Also, just take note of temperatures, and post so we'd know what works and what doesn't in the real world.
  14. tom_pearson

    tom_pearson Newcomer, in training Posts: 103

    Hmm I'm not too sure I agree with you when you say its best to have an equal amount of fans (in and out). IMO this doesn't seem right, I personally think the best way to cool a case is to have two intake fans which are GOOD air movers. then as many as possible near for example the power supply, the CPU, and the PCI/AGP cards. If you blow cool air onto for example the CPU the warm air will escape into the ambient areas, and in turn increase the case temperature (very slightly, but enough). If you fill the case with cool air, then drag it across the necessary areas, there will be no heat dissipation into surrounding areas. It will just be sucked OUT.

    Also I don't agree that the case is designed to stop "radiation" that could be hazardous. Unless you fill your case with nuclear waste!

    Final point. It's pretty obvious that if you have the side of the case off it will disrupt the whole flow of air around the case. This defeats the whole point of having fans on the case.


    I also have two intake fans, one at the front and one at the side. As I stated above this I think is the best method for air movement around a case.

    The ambient case temperature doesn't increase past 23*C, the CPU no higher than 45*C and the hard drive (also cooled with a HDD cooler) is roughly around 42*C (Obviously dependant on weather situations!)
  15. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    There's always some radiation emitted from any sort of electrical device. EMF or something I can't recall my Physics very well. But its only from high voltage devices where this is a problem. Which is mainly why they don't build houses under those nice big power lines, or near power pylons.

    You might think your comp runs at 12V, but remember that your PSU takes in power at 240V, which isn't really astronomical, but if you're like me, kinda lifeless sitting in front of a comp almost every waking hour, then you'd take it into account.

    I didn't say best to have equal amounts, its a suggestion if you don't want to worry about how the air flows and all that. If you can direct your air around the case perfectly, having no stagnant pockets, or having hot air going where you don't want it to, well, you can have all intake fans, no problem since only the hottest air will be expelled naturally from the pressure imbalance.

    Also, yes, if you don't mind the case temperature going up a little, no exhaust fans will do fine. But beware of other components which may not be getting that cool air, HDDs being the main target if there's no front fans. My comp with 3 fans doesn't run a front fan, but I've self designed heatsinks for my solo HDD, and so far its running pretty cool, so I'm not in a hurry to install one.

    Also, most PSU have 1-2 fans, and they're exhale fans (most, if not all). Raising your case temp will increase the running temp of your PSU, which lowers the total watts it can handle. Not a big problem, unless you're running a generic PSU with just enough Watts to go around.

    Most cases also do not have fans which blow directly into the AGP (nor can you install them) so your AGP might overheat too. Best way to overcome this is to install one of those PCI exhale fans (there you go, one exhale fan). Good on you if your case has a fan blowing at that direction, mine doesn't.

    So if you're reading this and going "I can't be stuffed looking into all this", install some exhaust fans. If you've got all the time in the world (like me), go ahead, and slowly monitor that airflow (coloured gasses work pretty wel for these purposes, the same stuff they use to check a car's aerodinamics). Or maybe use what I do: just run the comp, stress every part so it produces the most heat, shut it down, open it up, and stick my hand at various components and try to guess where could do with some extra airflow. Helps to keep the side panel ready to be opened.....
  16. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    I forgot to mention that its winter here in Aussieland, so the ambient temp is about 15-20C. (this is for my results 3 posts above).
  17. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    I've used the nice flat cables to my advantage. My top tan is an intake, and I've used that to direct the air from that to the motherboard, instead of blowing into the empty space.

    I don't really want to spend money on rounded cables so I know know if it really helps.

    But then again, it seems like the cables and bend so nicely so it seems to be blowing at the m/b, plus its not restricting airflow from fans. It does restrict airflow to my CD and DVD drives (and my Audigy2 bay), but not the HDD, as those are below all that flat cables. and its SATA, so its small rounded cables.

    I don't have power cables cluttering the insides of my casing, just one power line which has been shortened to provide just enough length (and some just in case) to provide power to the 5.25" bays and FDD, which is just below the 5.25" bays. HDDs receive power from another line which goes through the front of the casing (close to the front panel, which is hidden), so all you see is a small ittle tip near the HDD. Fans are powered through the third line, which is totally out of sight behind the casing (cept for one at the side, which draws power from the HDD line, also out of sight). Took me a week to do all that.

    FDD cable (the flat one) is left alone, but doesn't interrupt any airflow as it doesn't cover anything.

    Only problem with this is when I need to put a front fan (120mm), I'd have to re-look at my cabling.
  18. tom_pearson

    tom_pearson Newcomer, in training Posts: 103

    I don't think you quite understood. Where I said you should have fans near each area of heat production (like the CPU etc) Those fans should be exhaust fans. So that all the heat that is being radiated can be extracted out of the case as quick as possible so as not to affect the ambient temp.

    I do actually spend all day (and night) sat in front of a computer so I know what you mean! :slurp:

    But, like you said, the only radiation from a PC is mainly electromagnetic. My mother is quite a hippy and she actually has whats called a "Mouse" that detects the strength of these fields. Around the actual case of the computer there is minimal radiation. The main producer of electromagnetic fields is the monitor (in my case a 22" CRT). Not too sure about TFT's. But anyway I think we're trailing away from the original post!

    To save an argument, do what ever you feel necessary to cool your case! With there being so many shape and sizes of case, different component layouts and different temperatures to deal with there probably isn't just one way of dealing with the problem
     
  19. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    yeh, I agree with you there.

    not only that the case has many shapes and sizes, the motherboard has about equal number of different layouts. what works for someone may not work for another.

    These are just what some people do, take them as advice, and not the holy word or something. Then experiment, especially if tehre are conflicting statements. In the end, its your pc you're trying to cool, not theirs. You probably won't be getting exactly the same items other people have, so the fan and motherboard layout will be different, which will require different heat management strategies.


    About radiation, you might be right again, the CRT probably has the largest EMF emission. Doesn't mean that you gotta submit yourself to more from other sources :D
  20. Tedster

    Tedster Techspot old timer..... Posts: 10,074   +13

    intake implies suction.... an intake fan sucks in cool air.

    exhaust is exactly what is says..... blows hot air out.

    You want intakes on the bottom and sides and exhausts at the top and rear/top.
  21. Mugsy

    Mugsy TechSpot Maniac Posts: 410

    Side panel

    The original topic poster did not say he's running with the side off. That would be me. And I do have a table fan blowing on it. But what you said make sense. I will try closing my case up and see what it does to my temps.

    I don't want this to sidetrack the thread from the original poster's problem, so don't bother replying.
  22. Mugsy

    Mugsy TechSpot Maniac Posts: 410

    Side panel on was worse.

    Tried putting the side panel back on and the temperature jumped 6'C in four minutes. I quickly pulled it back off.
  23. tom_pearson

    tom_pearson Newcomer, in training Posts: 103

    thats fair enough... but all im saying is. if you have the side of the case off then theres no point having exhaust fans.
  24. Mugsy

    Mugsy TechSpot Maniac Posts: 410

    Confusion

    I think you are confusing my posts with the starter of the thread.
  25. CMH

    CMH TechSpot Chancellor Posts: 2,572   +9

    We kinda did answer his question, so I suppose this thread is "hijackable".
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