Heatsink Test Methodology

Benchmark Reviews is obsessed with testing CPU coolers, as our Cooling Section has demonstrated over the past few years. We've solicited suggestions from the enthusiast community, and received guidance from some of the most technical overclockers on the planet. As a result, our testing methodology has changed with every new edition of our Best CPU Cooler Performance series. Because of this, each article is really its own stand-alone product, and cannot be fairly compared to the others. Benchmark Reviews continues to test CPU coolers using the stock included fan (whenever applicable), and then replace it with a high-output fan for re-testing.

Manufacturers are not expected to enjoy this sort of comparison, since we level the playing field for all heatsinks by replacing their included fan with a common unit which is then used for every CPU cooler tested. Many manufacturers include fans with their heatsink products, but many 'stock' fans are high-RPM units that offer great airflow at the expense of obnoxiously loud noise levels, or, conversely, quiet fans that sacrifice performance for low noise. By using the same model of cooling fan throughout our heatsink tests, we can assure our results are comparable across the board. This is one of the more significant changes we have made to our test methodology, since many of the benchmark tests we have conducted in the past have compared the total package. Ultimately we're more interested in the discovering the best possible heatsink, and we believe that you'll feel the same way.

For each test, ambient room temperature levels were maintained within one degree of fluctuation, and measured at static points beside the test equipment with a digital thermometer. The Cooler Master V6GT and the comparison coolers used a common Thermal Interface Material of our choosing (listed in the support equipment section below) for consistency. The processor received the same amount of thermal paste in every test, which covered the ICH with a thin nearly-transparent layer. The heatsink being tested was then laid down flat onto the CPU, and compressed to the motherboard using the supplied retaining mechanism. If the mounting mechanism used only two points of force, they were tightened in alternation; standard clip-style mounting with four securing points were compressed using the cross-over method. Once installed, the system was tested for a baseline reading prior to testing.

At the start of each test, the ambient room temperature was measured to track any fluctuation throughout the testing period. Lavalys EVEREST Ultimate Edition was utilized to create 100% CPU-core loads and measure each individual processor core temperatures. It's important to note that software-based temperature reading reflects the thermal output as reported from the CPU to the BIOS. For this reason, it is critically important (for us) to use the exact same software and BIOS versions throughout the entire test cycle, or the results will be incomparable. All of the units compared in our results were tested on the same motherboard using the same BIOS and software, with only the CPU-cooler product changing in each test. These readings are neither absolute nor calibrated, since every BIOS is programmed differently. Nevertheless, all results are still comparable and relative to each products in our test bed (see The Accuracy Myth section below).

Since our test processor reports core temperatures as a whole number and not in fractions, all test results utilize EVEREST to report averages (within the statistics panel), which gives us more precise readings. The ambient room temperature levels were all recorded and accurate to one-tenth of a degree Celsius at the time of data collection.

When each cooler is tested, Benchmark Reviews makes certain to keep the hardware settings identical across the test platform. This enables us to clearly compare the performance of each product under identical conditions. Benchmark Reviews reports the thermal difference; for the purposes of this article, thermal difference (not the same as thermal delta) is calculated by subtracting the ambient room temperature from the recorded CPU temperature.

Please keep in mind that that these test results are only valid within the context of this particular test: as the saying goes, your mileage may vary.

Intel Test System

• Processor: Intel Core i7-920 Bloomfield 2.66GHz LGA1366 130W Quad-Core Processor Model BX80601920, core voltage set to 1.375V
• Motherboard: ASUS P6T V2 Deluxe (Intel X58-Express Chipset) with BIOS 1003

Support Equipment

• Lavalys EVEREST Ultimate Edition v5.50
• MG Chemicals Heat Transfer Compound 8610-60G
• Yate Loon 120x120x25mm fan, model D12SH-12 (88 CFM advertised @ 40 dBA) 12V/0.30A

All of the tests in this article have been conducted using vertical motherboard orientation, positioned upright in a traditional tower computer case. Heatsinks are positioned so that heatpipe rods span horizonally, with the fan blowing air out the top of the chassis. The heat sink fans are connected directly to the power supply (rather than motherboard headers) and run at full speed during the test. At the start of our test period, the test system is powered on and EVEREST system stability tests are started with Stress CPU and Stress FPU options selected. EVEREST loads each CPU core to 100% usage, which drives the temperature to its highest point. Finally, once temperatures have sustained a plateau (no observed change in average temperatures for 5 minutes), the ending ambient room temperature and individual CPU core levels are recorded thus completing the first benchmark segment. The time to reach stable temperatures varied between 10 and 30 minutes for the heat sinks in this test.

The second test segment involves removing the stock cooling fan and replacing it with a high-output 120 mm Yate Loon D12SH-12 cooling fan, then running the same tests again.

The Accuracy Myth

All modern processors incorporate an internal thermal diode that can be read by the motherboards' BIOS. While this diode and the motherboard are not calibrated and therefore may not display the actual true temperature, the degree of accuracy is constant. This means that if the diode reports 40°C when it's actually 43°C, then it will also report 60°C when it's truly 63°C. Since the design goal of any thermal solution is to keep the CPU core within allowable temperatures, a processor's internal diode is the most valid means of comparison between different heatsinks, or thermal compounds. The diode and motherboard may be incorrect by a small margin in relation to an actual calibrated temperature sensor, but they will be consistent in their margin of error every time.

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