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Internal Air Flow

The "first line of defense" in cooling the overall system is the fan that is used to provide overall air flow within the system case. This is normally the fan located within the power supply at the back of the case; some newer machines, especially full-tower cases, employ more than one fan, to provide more cooling.

It's important to realize that the fan (or fans) used in the case and/or power supply work by establishing a flow of air through the case. There are two basic designs used. In a standard baby AT style case, the power supply fan blows out the back of the power supply, and in doing so it draws air through the rest of the case and thereby, cools the components inside the case. In the newer ATX style of case and power supply, the power supply fan is on the inside of the case and blows inwards, pushing air throughout the case and drawing it in through the back of the power supply, exactly the opposite. In both cases, for the cooling to work properly, the flow of air must not be interrupted. The better, and stronger, the flow of air, the more cooling it will accomplish. If the flow is not established correctly, at best only some of the components will be cooled.

The flow of air also has an impact on keeping the inside of the case clean. In a standard baby AT case, the air is pushed out the back of the power supply, and replacement air is drawn in through all the small cracks and holes in the case. This tends to cause dust and dirt to be drawn into the case. One reason why the ATX form factor changed the design to blow air into the case instead of out of it, is that this isolates the in-flow of air in the case to one point, making it possible to use filters and other mechanisms to reduce dirt intake into the system unit.

Here are some rules of thumb and tips that you can use to ensure that the flow of air in your system is good, and to increase air flow in your case:

• Keep the Cover On: Many people think that running the system with the case cover removed will improve cooling since the components are exposed to the outside air. In fact, this usually makes cooling worse (unless you have something silly like a big external fan blowing right onto the system unit, which is impractical, to say the least). When you remove the case, the air that the power supply fan is pushing out the back of the case is replaced by air drawn from the room instead of being drawn across the components. As a result, many components will sit in stagnant air and get little cooling.
• Cover Exposed Expansion Slots and Holes: Any unused expansion card slots, drive bays, I/O port holes, or other crevices in the system case should be covered with inserts, faceplates, or even tape, to ensure that air flow is not being "short-circuited". Air will follow the path of least resistance, and if you have a big hole in your case near the power supply unit, most likely air will flow in there and right out the power supply, resulting in poor flow for the rest of the case.
• Use An ATX Form Factor System: The ATX form factor is better overall than the older baby AT style case and power supply. This is true not only because it provides better overall cooling, but also for several other reasons. It does cost more, however.
• Add Additional Fans: Some cases provide mounting positions for installing additional fans, and there are also fans that you can buy on cards that go into a standard ISA expansion slot. These can be useful, depending on what they are and how you set them up, although they are not necessary for most people if they follow the other suggestions listed here. A fan on an expansion card will improve air flow within the case, but not between the case and the outside world. An extra fan venting to the outside can improve air flow and cooling.
• Use a Large System Case: Larger cases have more room and therefore generally allow for better air flow and cooling of components.
• Arrange Your Internal Components Wisely: Devices that generate a great deal of heat should be kept as far away from each other as possible. If you install two hard disk drives in adjacent 3.5" drive bays in a typical system, they may end up with less than 1/4" separating them. This is simply not going to provide for cooling as good as if you had them several inches apart. This is all discussed in much more detail in this procedure dealing with internal system layout. You can also improve cooling by watching the location of ribbon cables inside the box, making sure they are not adversely affecting air flow.
• Keep the Inside of the Case Clean: Good airflow in the box doesn't help very much if none of the cool air can reach the components because they are covered with a thick layer of dust.

Next: Component Cooling

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