How the Case Rear Fan Improves CPU Cooling

Tests with the Case Closed

We tested the effect of the rear fan on the CPU core temperature, keeping the left panel of the case closed. There was no case fan other than the rear one. The left panel itself was solid, with no mesh or air intake. This means that, in these tests, the case ran with “negative pressure configuration,” which means that there were only exhaust fans (the case fan and the power supply fan), with no fan blowing air into the case.

The temperatures were taken with the case fan turned off, and then with it at 1,000 rpm, 2,000 rpm, and 2,700 rpm (full speed).

We repeated the tests with only one fan installed on the CPU cooler, and then with both fans installed.

The following table shows our results.

Rear Fan State Room Temp. CPU Temp. with Single Fan CPU Temp. with Dual Fan
Off 16 °C 60 °C 55 °C
1,000 rpm 16 °C 57 °C 55 °C
2,000 rpm 16 °C 55 °C 54 °C
2,700 rpm 16 °C 53 °C 52 °C

In the graph below, you see the temperature difference between the CPU core temperature and the room temperature with the case closed and with different rear fan speeds. Green bars are the results with two cooler fans; red bars represent the measures taken with only one fan at the CPU cooler.

Case Rear Fan

The measures show a crystal clear reality: the rear fan helps the CPU run some Celsius degrees colder. But it also shows that the temperature drop is more dramatic when the CPU used only one fan (seven degrees) than when we used a two-fan cooler (three degrees).

When using the CPU cooler in push-pull fan configuration, the temperature drop was smaller and actually only appeared when the rear fan was set at high speeds. In this case, the rear fan running at 1,000 rpm didn’t make any temperature difference from when it was turned off.

Notice that the same result obtained with one fan on the cooler and the rear fan running at 2,000 rpm was achieved with push-pull fans on the cooler with the case fan turned off. This means that the second cooler fan can assume the same role as the case’s rear fan, helping the CPU cooler to perform better.

Author: Rafael Coelho

Rafael Otto Coelho is a physicist with a master's degree in Education, and is a college professor in Brazil.

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