Opinion poll: Case pressure preference, and CPU fan direction


What is your preferred cooling setup?

  1. Positive Case Pressure, CPU fan blows onto it.

    6 vote(s)
  2. Positive Case Pressure, CPU fan blows away from it.

    1 vote(s)
  3. Negative Case Pressure, CPU fan blows onto it.

    7 vote(s)
  4. Negative Case Pressure, CPU fan blows away from it.

    2 vote(s)
By Marnomancer · 26 replies
Apr 2, 2012
Post New Reply
  1. Hello friends!
    It's summer time in this part of the world, and the need for good cooling has demanded acknowledgement again (Anyone who has lived in Texas knows what I'm talking about) :dead:
    To satisfy those needs on air cooling, I've come up with a mod which I will be posting in some time.
    Now comes the problem: The guide will be on a "works for me" basis. So how can I make it applicable for most people? :confused: To solve that problem (somewhat), I've got the option of a poll. :D

    Here are the things which need to be considered:
    1) Case pressure: Case pressure is the pressure co-efficient of your case's airflow. E.g. More intakes and less outlets create a positive pressure co-efficient, while less intakes and more outlets create negative case pressure. Note that this does not mean "all intakes, no outlets" or "all outlets, no intakes". It means intakes and outlets both working at different magnitudes.
    Though this may appear irrelevant to some, this has a lot of effect on the rate at which heat is vacated from the case.

    2)CPU Fan direction: This is a topic in which there is much disagreement. Some believe a fan blowing away from a CPU is better, some believe a fan blowing onto it is better. However, most modern systems have fans blowing onto the CPU. As this changes the airflow pattern in a case, it can fundamentally alter the scheme of my mod.

    As always, I'm open to suggestions for improvement. Any poll options will be added as necessary.

    Cheers! :grinthumb
  2. Leeky

    Leeky TS Evangelist Posts: 3,797   +117

    Added poll as per PM discussion with Marnomancer.
  3. fimbles

    fimbles TS Evangelist Posts: 1,185   +208

    Im getting " You may not vote on this poll"..

    Positive case pressure to keep dust out and cpu fan pointing out the back of case, though if i did not have a choice it would blow at the cpu, to cool the chipset too.
  4. Benny26

    Benny26 TechSpot Paladin Posts: 1,535   +51

    Same here.

    I have a 1 intake, 2 outtake setup, with the CPU fan blowing on to the processor. Never thought to change it, worked fine for years temperature wise.
  5. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    I'm getting the same "may not vote" thing. But maybe that's because I started this thread. Anyway I'll contact Leeky and let him know about the issue.

    I have exactly the same configuration as yours, with the only noticable dust being on the HDD. Do you experience a similar problem?
  6. Benny26

    Benny26 TechSpot Paladin Posts: 1,535   +51

    Yeah, spot on. The HDD that i have directly behind the intake (with the intake being at the front) gets a nice pile of dust every few month.

    It's no trouble though, comes off rather easy with one wipe.
  7. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    Exactly ;)
    TBH, even that dust can be slowed down by using filters at the intakes. I'm planning on using thinly sliced Scotch Brite Scouring Pads as filters for the mod. That should do the trick. Let's see how it works.
  8. Benny26

    Benny26 TechSpot Paladin Posts: 1,535   +51

    Not a bad idea. I have a set of double front grills myself, they give me a few extra weeks before cleaning is required.
  9. Julio Franco

    Julio Franco TechSpot Editor Posts: 7,668   +988

    Should be fixed now, go ahead and cast your vote :)
  10. Bobbye

    Bobbye Helper on the Fringe Posts: 16,334   +36

    First entry checked with no problem.
  11. SNGX1275

    SNGX1275 TS Forces Special Posts: 10,742   +421

    I have a 120mm front fan blowing air in across 3 hard drives (in the spaces between 3 drives in top, bottom, and middle of a 5 drive bay section). Then I have my graphics card which sucks air out. My CPU fan is a CNPS9500 LED with air blowing towards another 120mm case fan blowing air out. Then my PSU has a bottom intake fan, and then a fan blowing out the back. I have no side vents, but the front of my case is a wire screen backed by some low density foam rubber. That does a fair job at keeping dust out, and it allows air flow in wherever I don't have a drive. So negative pressure case, and the CPU fan blows through the heatsink fins rather than pulling air.

    There has been debate here (and elsewhere on the internet) many years ago on blowing air onto heatsink or sucking air through it. Sucking air through is a bad idea was the conclusion. I'd be interested to hear if anyone is using that on some more exotic heatsink design with more success than blowing.
  12. Leeky

    Leeky TS Evangelist Posts: 3,797   +117

    I don't even use a fan as my heatsink is the water cooler socket for my Corsair H50 water cooler.

    My preferred cooling setup is this though (Cooler Master HAF 912+ case):

    1. Front 200mm fan sucks air into the case
    2. side mounted 140mm fan blows hot air out of the case
    3. top mounted single 120mm fan (H50 rad takes up too much space to fit 2nd) blows air out of case
    4. rear exahaust has Corsair H50 radiator mounted with 2x 120mm fans (push/pull configuration) blowing air out of case.

    That seems the best for cooling for me, though the fan setup makes it a total dust magnet and I find I have to clean it weekly now I have the case mounted on the floor.

    I do find that it cools my hard disks much better this way though. When the side and top fans blew it it disrupted airflow inside the case and made them very warm on one side of the disk, and cool on the side facing the front mounted fan. This setup keeps them cool even after 18 hours of continuous running.

    My GPU is a AMD Radeon HD6870 which uses a single large fan that warms the inside of the case as well. It is not the usual reference design that exhausts out the rear of the case. So I find exhausting all hot air out of the case to work very well. Temps on the board seem okay as well, despite the lack of direct airflow onto components from any fans.
  13. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    I will take that into consideration.
    The key is that hot air should be transferred out quickly, it should not recirculate, and cool air is sucked in with the least possible impedance by filters. The only thing I have to worry about now is the HDD and RAM cooling. It isn't falling in my airflow pattern well. This project is getting far more massive than I had anticipated.
    It is captaincranky's opinion that I'm waiting for now. As much as I hate to admit it, he always has something valuable to say. Let's see what others have to say till then.
  14. fimbles

    fimbles TS Evangelist Posts: 1,185   +208

    Im curious as why so many people have chosen negative air pressure?

    I was led to believe that this encourages dust to be sucked in to all the little gaps in your case, And can cause a vacuum effect with shrouded gpus in the worst case scenario?
  15. red1776

    red1776 Omnipotent Ruler of the Universe Posts: 5,224   +164

    Negative air pressure does attract more dust, but it draws more outside (cold) air through the system. It gets the air in to equalize/diffuse with the ambient temp, and gets it out of the case faster. whereas positive pressure has the incoming air hanging around a bit longer to absorb more heat and keep the case ambient a bit higher. It traditionally has been a few degrees cooler than a positive pressure setup. But then you have a lot of different configuration and placement issues to consider....but that is why most 'enthusiast's opt for it. However you are talking about a system that only has the compulsory front intake fan and rear exhaust, you are generally not talking a huge difference. Many more people have a problem with fan layouts with airflow that work against each other (see the 'all important side-fan') before they even get to the pos/neg issue.
    fimbles likes this.
  16. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    When you have positive pressure, i.e., have more fans blowing in air, you are also blowing in dust. I wonder how people can overlook that simple logic.
    Positive case pressure brings in cool air, and tends to keep it trapped in, creating hot air pockets. Neg pressure, on the other hand, removes hot air out.
    Cooling depends on not how fast cool air is moved in, but how fast hot air is moved out.
    Looks like I'll have to explain this in more detail in the guide to clear any misconceptions.
  17. red1776

    red1776 Omnipotent Ruler of the Universe Posts: 5,224   +164

    Red1776 said:
    Marnomancer said:
    1) We said the same thing...

    2)Nobody is disputing that there is dust in the air, neg or positive. Negative pressure just introduces more air through the system, thus is a bit dustier.

    Marnomancer said:
    3)Any chance you might do that without your superior condescending BS attitude?
  18. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    No offence, but I'm trying to be superior. My apologies if I offended anyone. I was merely stating that it is overlooked by most. Some people state that it 'keeps dust out'. Which I found preposterous. If filters are used at every possible opening, the accelerated dust accumulation can be slowed down. I'm saying that from experience.
    Apologies again, though I'm still confused over what I'm being offensive.
  19. red1776

    red1776 Omnipotent Ruler of the Universe Posts: 5,224   +164

    You really don't know why that would be offensive?
    Because for those who are not up on the attributes of the types of case pressure, it's not 'simple logic that will be missed'
    ...sorry you weren't intelligent enough to figure that out....
    see how that works? :)
  20. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    Ahh...I see. :) :haha: :rolleyes:
  21. fimbles

    fimbles TS Evangelist Posts: 1,185   +208

    Great explanation. Thanks red :)

    I did not overlook the fact that positive fans also bring in dust, but my fans are filtered. The small gaps in my case however are not.
  22. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    I have filtered those small gaps too :haha:. My system stays clean enough. Or it could be just an environmental factor. I'm now working on making the filters more efficient. To allow more airflow, yet keep out dust. Let's see how it goes. :)
  23. Dawn1113

    Dawn1113 TS Booster Posts: 322   +65

    The planned guide will be helpful for noobs like yours truly. I had problems configuring the fans on my case and it took a while before my brother and I settled for its present arrangement. I followed Corsair's recommendation in setting up my H100 -- so I have 4x120mm fans blowing air in from the top of the case and a single 140mm fan acting as exhaust through the back. (The air blowing into the case is actually warmed by the rad -- which has always worried me.)

    I would have preferred to have the 200mm fan at the side panel of the HAF X blowing air out. But being near the PSU, my lower GTX 470 was idling at 52°C with that fan acting as exhaust. So my brother reversed its direction and used the shroud that came with the HAF X to blow cool air directly at the GPUs. That reduced their temps. They began to idle at around 42°C to 45°C. The 230mm fan in front of the case also blows fresh air into the case through my HDDs.

    So presently I have all these big fans blowing air into the case. Only the built-in exhaust systems of the GTX 470s and a single 140mm move warm air out. Seems pretty uneven, yes. But my CPU idles approximately 32°C to 35°C hottest (I used HWMonitor to check) -- which, I guess, isn't too bad. The highest I've ever seen my temps go while gaming is 45°C.

    I'm sure the guide will help me improve on my present set up -- as I do worry that it gets a tad hot inside that case.
  24. Marnomancer

    Marnomancer TS Booster Topic Starter Posts: 723   +51

    Are you sure it's the temperature of the CPU package and not just the core? I have a room temp of around 32°C, my CPU core idles at 29~31°C, and my CPU package idles at 42°C (some mods are already into place, earlier used to be 45°C). So if it's the core temp you're talking about...given your rig,we're looking at...50°C+. However, it also depends on ambient temps. Which temperature monitor do you use? SpeedFan and HWmonitor will give you the CPU package temps, i.e., the temperature of the CPU as a whole. CoreTemp only reports the core's temp, true to its name.
  25. Dawn1113

    Dawn1113 TS Booster Posts: 322   +65

    Now I'm confused. Haha! I use HWMonitor and Argus. My temps are at 33°C right now -- hottest. Ambient is around 27°C.

    Sorry for the noob error. Maybe I should correct that somewhat so as not to confuse fellow noobs. Wait a sec... There.

    Thanks for pointing that out, Marnomancer.

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