Guide to Proper Case Airflow Design Airflow and case circulation: Airflow: Rule #1 - Airflow is best if it can flow in one direction only and it is always better off (stays stronger) flowing in a straight line of sight direction if possible. Also always cut out a hole where you mount a fan, never mount it behind those predrilled "cheese grater" holes for fans or you won’t get any kind of good airflow. cutting out the opening for the fan can increase airflow by as much as 70% more then the fan trying to get air to pass thru the holes. the newer and larger openings and fan grill designed cutouts are ok but if you aren't sure then test them by feeling the airflow with the fan outside the case then in the case and if its unrestricted you shouldn't be able to tell the difference. Redrill all those small holes in the vents at the back of the case with a 3/16" drill bit to increase air from that spot and if you have the larger hexagon shaped holes that are already larger then it should be ok the way it is. another thing to note is noise, a fan is always louder when mounted onto some type of a stamped metal grill then with it just mounted over an open hole, sometimes its way louder. Heat: Rule #2 - Heat naturally rises so to remove heat the easiest and most efficient way it is best to draw air in from the cases lowest points and exhaust it from the cases highest points. The Direction of Airflow: The airflow can be directed into the case from a few different ways as long as you remember rules 1 & 2 above. The most common setup for cases is to intake air from the bottom front and exhausted out the top and back. The reason they do it this way is it takes best advantage of rules 1 & 2 above. The air is drawn in from the coolest point (bottom front) and moves in a lazy "S" upwards to flow across the motherboard and CPU and then carry the heat from the case out the rear exhaust fans (top rear and psu fans). Fans: Side fans - side fans can and do interfere with this "S" flow of air so keep this in mind if you’re thinking of a high cfm side fan. It may improve cooling in one spot and allow a "dead spot" for airflow somewhere else. Side fans are great cooling aids for direct cooling but reek havoc on proper airflow thru the case because they just cause the air to flow in a circular pattern and the heat has trouble leaving the case so it makes one spot cooler while making everything else in the case constantly stay warmer so while side fans can be helpful, don’t go overboard with the cfms. To reduce the interference from side fans most cases use air ducts to direct the cool air right into the CPU fan so it will not interfere with airflow through the case so side fans should never be used without air ducts to prevent the whirlpooling of the case airflow. Video Cooling: VGA - the video card area tends to be a dead spot for airflow. This is why they have fans now that exhaust hot air directly out the back of the case. Adding a side fan blowing cool air into this bottom corner helps "stir" the air so heat doesn’t get trapped there and it can rise up and be exhausted by the rear fan. This works well as long as you don’t over do it to the point that it will interfere with the vga cooling fan and the airflow going through the heat sink. Just remember the fan is there to stir and mix the air in that bottom corner dead spot and that’s all. It should not blow high cfms directly across the heat sink or its fan or you could actually reduce its cooling ability by canceling out the airflow moving across and though the heat sink. you also don't want to mess with the airflow coming from the front of the case so its important to use lower cfm fans if you want to add more cooling to that area. Balanced Airflow: Push / pull or Fan In / Fan Out System - It's not as easy as just having your fan cfms and sizes matching in the front and rear because they don’t always give you evenly balanced airflow through your case due to obstructions and things like side fans or large video card fans that exhaust inside the case. This is because it is a lot harder for a fan to pull air into a case then to blow it out of the case so you need a little more cfms from your exhaust fans to equal out the airflow and help the intake fans to draw in air easier so don’t just assume two 80mm 45cfm fans in the front and two 80mm 45cfm fans in the rear will give you a balanced airflow, they wont but it should be close enough that you don't really notice it. Positive Pressure Airflow System: More Air in Than Air Out - the benefit to this type of system is supposed to be that it pulls in less dust than a negative airflow system but this is a false idea. Weather the fan draws the air in or directly blows it in it is still the same air from your room with the same amount of dust in it. If your room is dusty your case will be dusty. A simple air supply test is to just check the amount of air your system is exhausting through the small holes in the back of your case, if you can feel a gentle draft coming out then you are restricted and should adjust the airflow by reducing the cfms of your intake fans or making bigger exhaust openings to balance things out. Negative Pressure Airflow System: More Air Out Than Air In - the benefit to this type of system is they are quieter because they have slower fans that move less cfms so they run quieter. one main disadvantage is because of the slower airflow it can build up heat quickly if the airflow is restricted in any way so you need to be sure you don't block the case air intakes and the first time you test your system with the new airflow design its best to check your temperatures are in the safe ranges during heavy gaming activity when heat can build up quickly. Often people will use fan controllers to speed up fans for better but noisier cooling while gaming and yet turn them down to still have a nice quiet computer when they are just doing normal computing activities. Why does a positive airflow system get less dusty than a negative airflow system? Both systems have the exact same amount of dust moving through them but it tends to settle on things in a negative airflow system more, only because the air is moving slower. Think of a fan blowing feathers around in a small room, as long as the fan keeps blowing fast they all stay airborne but put the fan on slow speed and everything will be covered in feathers. The same applies to dust in your computer, it is the airflow "inside" the computer that determines how fast your computer gets dusty. You can reduce dust building up by putting a fan inside the case just to keep the air stirred up so dust won’t settle and it can then be exhausted out the back of the case by the fans but then everything in the case would have poorer cooling because of this air whirlpool going on. Air Supply Test: A simple air supply test is to just check the amount of air your system is exhausting (rear exhaust fan) and also checking the air your psu is exhausting is to just remove the side cover on your computer. It will always move more air with the door open so if you notice only a little difference then you are fine but if you notice a big difference then you may need to investigate where your restriction is and provide a larger or less restrictive air intake opening. A person with high cfm exhaust fans who doesn't have proper sized intake openings for his case can actually cause a slight vacuum inside the case and prevent the psu from getting enough air because it is being held back by that vacuum causing the psu to overheat. Some PSU that have high cfm fans can have the reverse effect and cancel out the rear exhaust fans ability to remove air from the case. Most problems people have with negative airflow systems are with the proper sizing of cfms and the size of the fans and not the negative airflow design itself. If you aren’t over clocking, a properly designed negative pressure airflow system will always work great with just a large 120mm rear exhaust fans only and no intake fans at all unless spot cooling is needed for a hot spot. It just needs to have an unobstructed opening (no cheese grater holes blocking the front fan spot or air filter) that is equal to or bigger than the total size and shape of the exhaust fan openings. If for example, if you have two 80mm exhaust fans (plus the 80mm psu fan) then you need an unobstructed opening that is equal to four 80mm holes with open grills. This won’t work with filters because with the extra restriction of the filters you don't get proper airflow. it also works fine with just one 120mm rear fan and the openings for the 80mm side fan and 80mm front fan will allow more then enough air in to have good balanced airflow. in this situation you would only cut out the front fan cheese grater grill not the side fan because it isn't needed and it looks better. Another overlooked obstruction is the front panel cover; it can restrict airflow no matter how big the opening is behind it so test with and without the front panel in place to see if you need to cut back the plastic in an out of sight spot such as the bottom edge or if need be then air must be brought in from a different place (maybe the bottom case panel).