How the Case Rear Fan Improves CPU Cooling

How We Tested

We tested different situations using the same testbed system that we currently use to test CPU coolers and thermal compounds, which is fully described below. Our Core i7-860 (quad-core, 2.8 GHz) CPU, which is a socket LGA1156 processor with a 95 W TDP (Thermal Design Power), was overclocked to 3.3 GHz (150 MHz base clock and 22x multiplier), and we kept the standard core voltage (Vcore).

We used a Corsair A70 CPU cooler, which is a typical tower cooler that can be mounted with one or two fans.  We used the thermal compound that comes with this cooler.

The fan used in the rear of the case is the SilverStone FM123. We chose this fan because it is very strong and it has a potentiometer where we can set its rpm to any value we choose. We repeated each test four times with the fan turned off, at 1.000 rpm, at 2.000 rpm, and at 2.700 rpm, which is the maximum speed for this fan.

Case Rear FanFigure 1: Fan used in our tests

Room temperature measurements were taken with a digital thermometer. The core temperature was read with the SpeedFan program (available from the CPU thermal sensors), using an arithmetic average of the core temperature readings.

Figure 2 shows our test system, with the rear fan installed and only one cooler fan. Figure 3 shows it with both cooler fans installed.

Case Rear FanFigure 2: Cooler with one fan

Case Rear FanFigure 3: Cooler with two fans

Hardware Configuration

Operating System Configuration

  • Windows 7 Home Premium 64 bit SP1
  • NTFS Filesystem

Software Used

Error Margin

Since both room temperature and core temperature readings have 1 °C resolution, we adopted a 2 °C error margin, meaning temperature differences below 2 °C are considered irrelevant.

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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