The hot air then rises and goes back through the power supply heating it even more. For this idea to work you must have good heat sinks in the power supply and effective fans exhausting the air through the bottom of the case. I tried everything from adding additional fans and making sure the air flow was directed from the top to exhaust through the bottom of the case, with out much improvement. I even tried turning the power supply upside down and reversing the flow of the air, again without much improvement. I installed it that evening and my computer is now running cool.
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I know this was well worth the money. The next step is to insure there is an adequate flow of air into and out of the case. I have a great computer desk which has a compartment for my full tower computer. This compartment worked fine for my old 486 computer which had vents on the front and back of the case, but my new case has vents on the sides which were obstructed by the compartment. I drilled holes through the compartment at the level of the vents in the case.