How To: Properly Plan And Pick Parts For An Air-Cooled PC, Part 1

Cooling Theory Made Easy

Energy Conservation

We don't want to bore you, but it is important to emphasize what a large undertaking the right cooling system can be. PCs are among the most inefficient appliances of all time, because much of the electrical power they use is converted directly into heat (energy). There's no getting around it; you just have to live with that reality.

Even a simple 40-watt light bulb emits enough heat to melt plastic and trigger a fire. PCs use 60 watts or more at idle. Under load, that number can quickly jump tenfold or more! Bear this mind. It'll frame our conversation and help you respect what a tough task PC cooling really is.

Heat must be dissipated, enough so that the PC’s components don't exceed a certain maximum temperature. The task is achieved in several stages:

Dissipation from the surface of the heat-producing component (be that a CPU, GPU, or motherboard voltage regulator)
Absorption in the heat sink and transport to the cooling fins
Emission of heat to the air (which, unfortunately, conducts heat poorly)
Evacuation of the hot air from the enclosure

In steps one through three, we use commercial heat sinks with fans, which are designed to fit as many interfaces as possible and can sometimes cause installation issues on more elaborate or specialized platforms. Fortunately, most of those issues are easy enough to solve. That last step, however, requires advanced planning, so we'll start by taking a look at airflow.

This is directly related, of course, to the placement of the components within your enclosure. So, on the next page, we'll start by taking a look at the basics of power supply construction, cooler direction, and case fans.

Stack Effect:

Hot air rises, while cold air sinks. So, the upper part of the housing is normally the warmest. We have to keep this basic principle of physics in mind when planning a cooling system.

Create a new thread in the US Reviews comments forum about this subject
This thread is closed for comments
111 comments
Comment from the forums
    Your comment
    Top Comments
  • Mark Heath
    Good timing as the Australian summer approaches. You guys in the US think you have it hot :S
    19
  • Other Comments
  • compton
    After reading the charts of PSU placement and the GPU cooling diagrams, I'm even more convinced that my Lian Li PCA05-NB is a great solution. The motherboard is upside down, so that GPUs (In my case an axial fan gpu) faces towards the top. The CPU is now at the bottom back of the case and with the rear fan acting as an intake and not exhaust, you get great CPU cooling. The PSU mounts in the bottome front as well. The great part of this design is all the heat ends up in the top. As an option, you can vent the top to release the heat rising from the GPUs, but I like the case because it has very little venting. Through unusual case design and careful component selection I have an almost silent system - but with overclocked CPU and GPUs. The front fan is the exhaust, but has a bezel over it. With a few bucks worth of acoustic dampening material I can even hear myself think sometimes. I regard low temps and low noise output to be two sides of the same coin, but I know that many seem to not mind loud systems and mainly just care about temps. It's never been easier to build a near-silent system, even with high performance gear.

    If you plan ahead of time, you can make a super quiet and cool running system. It's easier to build a cool and quiet system from the start than retroactively go back and try to make a noisy (and/or hot) system quiet with great temps.

    I'll be waiting for article 2.
    1
  • Mark Heath
    Good timing as the Australian summer approaches. You guys in the US think you have it hot :S
    19
  • buzznut
    Guten hunger YAH!
    0
  • JOSHSKORN
    I want my next PC to be able to play Crysis AND make me hot dogs and Iced Frappuccinos.

    All kidding aside...curious though, the test setup is on AMD CPUs. What about Intel CPUs? I would assume many of the concepts are similar.
    -4
  • 100100
    Finally! A definitive article on how to air cool effectively! :D
    8
  • frostmachine
    Great guide. I live in a perpetually hot n dusty place. This will come in handy.

    Would be better if there's some tips on dust management.
    7
  • beetlejuicegr
    heh i am just showing you a pic from my pc that the airflow is totally different because there is a watercooling system on the cpu, i hope that the picture is self explanatory for all.
    http://img828.imageshack.us/img828/7030/mypcairflow.th.jpg
    -7
  • amirp
    Hey I have a question... for the PSU you say to not put it in upside down (ie. with it's opening facing up into the chassis..) but this is how I have mine in my ANTEC300 case since there is little room between bottom of case and the PSU if mounted right-side up. So what should I do?!!
    -3
  • BulkZerker
    amirpHey I have a question... for the PSU you say to not put it in upside down (ie. with it's opening facing up into the chassis..) but this is how I have mine in my ANTEC300 case since there is little room between bottom of case and the PSU if mounted right-side up. So what should I do?!!


    PSU's don't pull that much air, normally. So unless your Unit kicks it's fan speed way up there then don't royy abotu it and do as suggested. If it doesn't work then you can always just flip it back to where it was.
    2
  • darkrydr3
    BeetlejuiceGr, your cpu core temps are pushing 70 or 90 degrees C... thats hot!
    5
  • MAGPC
    Mark HeathGood timing as the Australian summer approaches. You guys in the US think you have it hot :S


    LOL, you both in the US and Australia think that it is hot at your home.
    Come taste the hot weather + high humidity in the Gulf countries.
    6
  • marraco
    Great article. It would be good to have also words on noise and dust (filters)
    7
  • amk-aka-Phantom
    MAGPCLOL, you both in the US and Australia think that it is hot at your home.Come taste the hot weather + high humidity in the Gulf countries.


    Seconded :D
    1
  • ickarumba1
    This is a decent article.

    However, the compilation of articles on Silent PC Review provide much more thorough details on air-cooling effectively. SPCR also comments on noise characteristics, with detailed comments on specific component selection. It makes this article kind of redundant.
    2
  • v73
    So how is cooling in system with bottom PSU, downdraft cooler, top and rear exhaust and NO side fans (without any holes for silent system)?
    -2
  • Anonymous
    Based on this the tower format is a heat failure as the best orientation would be for the motherboard to be laid on the floor of the case. One other aspect that wasn't mentioned and I don't know how much of an affect it would have, is Bernoulli principle that dictates moving air to have reduced pressure and temperature over surrounding static air. Tunnel structures for airflow to assist air speed inside the case?
    0
  • jemm
    Great work! As someone pointed out, dust intake is a problem when you have lots of fans pulling the air inside the case. While not all places are dusty, my place sits behind a school and there are dust everywhere. So my solution come from Organza, a thin, plain weave, sheer fabric traditionally made from silk. I fixed the fabric outside the case, and it works to filter the air.
    2
  • ojas
    great article, was going to revamp my cooling system in december anyway, this article helped a lot, and confirmed a lot of my suspicions (like the side fan).
    only prob with the side fan is that most manufacturers don't include dust filters on the side went, even if the front and psu intakes have it. you can always make/buy one though...

    MAGPCLOL, you both in the US and Australia think that it is hot at your home.Come taste the hot weather + high humidity in the Gulf countries.

    i was going to make a similar comment regarding Indian summers :D. I only see my hard drive below 30*C during winter!
    3
  • Anonymous
    You did not address or test air pressure. I spent many days testing multiple formats such as the tests above at my previous position and when I included air pressure, the whole story changed.

    Positive air pressure in a case, that has optimal channels for air movement, will cool components better than neutral, or negative pressure.

    All else equal, the positive air pressure creates more small eddies that pull more heat from the surface of components, which would otherwise be missed.

    You can test this, grab a good tower case, with a bottom mounted PSU, well groomed cabling, and make sure the case has no perforated walls (which defeats the purpose of air pressure testing). If you have 6 fans, 3 point in and 3 point out, in any configuration, it will cool less effectively than arranging the same 6 fans in a 4 in 2 out configuration.

    Try it and see if you get the same results...also any thermodynamic engineers care to join in? I am no engineer, just interested.
    3
  • ramicio
    A 60 watt light bulb emits approximately 90% of its energy through heat, so about 54 watts of heat. A computer drawing 60 watts at idle isn't going to be a particularly warm one. The power supply alone is 80%+ efficient. You just can't compare a light bulb's heat output to a computer's. Plus, a computer's heat is spread out over a higher area.

    As for the case you're working with in this article...I would not recommend it to anyone. These cases with the hard drives mounted sideways may be slightly handy, but there is basically no airflow over them. I don't see why a person with a simple tower would need quick removal. If you want server-type features, man up and buy real server hardware. Hard drives don't need much airflow to stay cool. There is no need to add anything to a hard drive to cool them, they should be properly cooled in the first place.
    -6