You don't want all the fans blowing out if there are fans in the front and back. This will disrupt flow and cause dead spots increasing operating temperatures in certain areas of the computer. With one blowing in and one (plus power supply fan) blowing out, there is a general flow pattern.
There are many ways to keep your computer cleaner, some good and others will cause heat problems. The first thing that has to be done is figure out how much air flow is flowing through the computer.
Are the case fans 60mm, 80mm, 92mm or 120mm in size? Are the grills very restricted? (little holes for the fan to suck air through our large cutouts for free flow) The small holes will destroy your air flow as 12 volt DC fans can't handle the pressure on the blades. If the restrictive holes are cut out and you add a wire fan grill, it will increase the air flow tremendously!
Why would you want to increase airflow--won't that increase the amount of dust flowing into the computer? It sure does! The point of increasing air flow is due to a filter cutting the amount of airflow in half. A filter that is cheap and won't cut much airflow from the fan is nylon panty hose. It will catch the dust bunnies, pet hair and carpet fibers and prevent them from clogging the heat sinks.
One way to evaluate how well your airflow is going up (unrestricted fans) and see if the filters are killing airflow is to check the temperatures. There is a program called Speed Fan out there that reports the CPU on-die temperatures (AMD Athlon64 and Intel P4) tells you what the motherboard temperature is and (if your hard drives are recent) tells the hard drive temperatures.
I have these programs running and know when it is time to clean my small desktop hometheater PC. With the computer dirty, make a file and record the temperatures. Clean the computer and record the temps clean (they will be lower)
If your fan grills are restrictive, cut them out (or have a person that knows how to take computers apart cut out the grills---metal shavings and electricity don't mix) Take the temps again and see the difference...take the fans out and put a piece of panty hose over the fan (put the fan inside the panty hose so both layers will catch dirt) Install the fans and see how much the temperatures change, it should be slight.
If you want better filtration and still keep the computer cool, it can be done but takes more effort and some additional costs. This is how to do it.
Say your computer has 80mm case fans and there is space on either side of the fan for a larger 92mm or 120mm fan. Cut out the case for the larger hole (a CD is the perfect template as it is 120mm for those 120mm fans) Get a rheostat (variable resistor) and plug the fan into the device. This is to speed up and slow down the fan for adjusting the airflow. Wrap the fans with panty hose and adjust the fan flow for midway between max and minimum speed.
Take the temps again and see if it runs cooler than it did when it was clean. If it does you can either add another layer of panty hose or (if it is loud) slow down the fan to drop the airflow. Adjust to approx. the same temps as the computer is clean.
Another way to keep it clean is to not allow the heat generated by the CPU to mix with the air in the case. Yep, this is gonna cost some money, take a little effort and if you don't know what you are doing...can damage or destroy your computer.
Say you know a guy that builds his own computers and will help you replace the CPU heat sink. The stock heat sinks on computers are not the best thing to cool your computer in lower airflow conditions. The one I find works for me when it comes to this trick is the Thermalright XP90 heat pipe heat sink ($40) The good thing about the Thermalright XP90/XP120 series is the fan does not have to blow down into the heat sink to keep it cool. My fan sucks air off the heat sink and blows straight up and away from the rest of the components. The hot air blows into a short duct that exhausts hot air out the top of the case. (It is a desktop case that is about the size of a stereo receiver) If the heat is pulled off the heat producers in the case and ducted out, it will not heat up the case...just help exhaust the case.
Say you have a tower case sitting on the floor. Have your computer friend remove the stock heat sink, clean off the thermal paste (gooey stuff between the heat sink and CPU die)put a thiiin layer of new thermal paste on and slap on the much, much, MUCH larger Thermalright XP series of heat sinks. The gigantic thing will drop your CPU temps down at least 10C (18F) Make sure it works correctly and move to the next step.
Take the side panel from the computer and install a duct to match the 92mm slow speed fan (for XP92) or 120mm fan (for XP120) The plastic hose has to match were the heat sink is and should be quite a bit larger than the fan for clearance. The hose should fit over the entire depth of the fan but not cover the heat sink portion to allow airflow to the fan.
Fire it up and put your hand over the duct and feel the airflow. Check the temps again and notice how much cooler the computer is running. You can turn down the case fans a bit more if your motherboard, hard drive and CPU temps are running cool. Yep, there is another step on your quest.
It all depends on what computer you are using and if it runs a performance video card. The fastest and hottest video cards from nVidia (6600GT, 6800 and 7800 series) and from ATi (X700/X800/X850) generate some serious heat. A nVidia 6800 Ultra can generate over 80 watts of heat which is more heat than a Athlon64 3800+ (45 watts)
If your computer has a slow video card or intergrated video (most Dells, Gateways, Compaqs etc) don't worry about it. If your son is playing Doom III at high resolutions, better look at the video card! Artic Cooling makes a video card specific cooling system called the Silencer. It has a large 72mm fan blowing air across a ducted heat sink that ducts to the back of the case and out. The slot next to the video card is taken up by that beast so if you can afford the slot, your stuck.
My PC uses the Silencer and the fan runs at 7 volts (rheostat turned all the way down) The card runs 8C (15F) cooler than stock and is...well...silent. I can feel the low airflow blowing off the card at the back of the computer. I presently have an Asus X700 Pro 256MB PCI Express video card and it runs along at 35C (95F) Have the Silencer on your wazoo video card now? Any more steps? Well... yes there is!
On your motherboard there will be another heat sink on the Northbridge chip. Some of these have tiny, whiney little fans on them. Replace it with a Zalman Northbidge heat sink or Cooler Master makes one with heat pipes (they are very large and won't fit some motherboards...better get your computer buddy back at your house!) This gets ugly!
Remove the motherboard from the case and take off the Northbridge heat sink (should be two plastic push pins holding it on) Remove the pins, pull the stock heat sink off and clean the Northbridge chip of thermal goo. Follow the instructions for the Zalman or Cooler Master large heat sink and install it. Put the motherboard back in and check if the temps have changed. Most likely it won't but in my case, the motherboard thermal temp probe sits near the Northbridge and my temps fell 6C (10F)
Now your computer has huge heat pipe heat sinks/ducted video card heat sinks and large filtered fans. Check the temps and adjust the fan speeds accordingly. Are we done yet? All depends... are you the kinda guy that wants it all?
If you are running a recent Intel Pentium4 that uses the Prescott core, replace the motherboard and CPU with either a Athlon64 or PentiumM laptop processor. They generate much less heat, will turn their voltage down when surfing the net and just sitting there and in case of the Athlon64, most motherboards will turn down the CPU and case fan speeds under low load conditions. If playing a game, editing video or running the processor at 100% it will ramp the fan speeds back up at certain temperatures to cool itself. Not good enough? Yep, one LAST step!
Buy a Zalman monster tower with huge heat pipe heat sinks to transfer the heat to the outside of the case. Look Ma! No fans! Talk about lack of dust! One little thing though, it costs $1,200 for the case so...
As you can tell, it all depends on how far you want to go with this. You might of asked to borrow a minimag and I just handed you the plans for a 400+ lumen multiple Luxeon megalight, if so I am sorry.
And yes, my computer runs along very cool, almost silent and a very small case (Athlon64/X700 Pro and many cooling tricks) It has been running almost 6 months now in the severe dust of N TX and southern Turkey without a cleaning. Even without filters, the temps have only jumped 8C (15F) just in time for its cleaning cycle. It has three case fans, a XP90, Artic Cooling Silencer and large Zalman Northbridge heat sink.
Have fun with it and if you don't know how to mess with a computer... get someone who does.
