The rule of thumb is that you pull air from outside the case through the radiator.
When you put a load on the computer, it's going to start generating heat inside the case, which in turn means warmer air traveling through the radiator on the way out of the case. You can have all the air coming into the case that you want, but if you're not venting the heat of the components effectively, it's just going to get trapped in the case. With the fans on the rad pulling air from the outside, you're making sure the coolest ambient air is being used to cool the radiator [and by extension your processor].
You still need good exhaust to vent the heat, however.
keep in mind, the above is not the end all be all. There are several schools of thought on most efficient cooling, and you have to take into account case design, graphics card airflow design [mine actually vent into the case, as opposed to something like a reference card design, which is enclosed and vents out]. I went with the above because that's what corsair recommended, and the theory seemed sound.
and don't forget, you can also add two more 120mm fans on the other side of the H100 for a push-pull configuration to help cool the radiator as well. Unfortunately, the H100 doesn't come with extra screws, but you can get the dimensions online and get them from a local hardware store : )
Edited by Sen, 15 November 2012 - 01:43 PM.
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