Why Reviewers Lock Fan Speeds in Thermal Benchmarks
Hardware reviewers frequently lock fan speeds to a fixed percentage during thermal benchmarks to eliminate variables and ensure fair, repeatable comparisons across different computer components. This article explains why isolating fan behavior is critical for accurate testing, detailing how it removes the influence of inconsistent factory fan curves, highlights the true efficiency of a cooler's physical design, stabilizes boost clocks, and provides reliable data for consumers.
Eliminating the Moving Target of Dynamic Curves
By default, computer fans operate on a dynamic curve, meaning they spin faster as temperatures rise and slow down as components cool. While this is ideal for everyday use, it ruins scientific testing. If a fan constantly changes its speed during a benchmark, the airflow changes with it. Locking the fan to a fixed percentage—such as 50% or 100%—ensures a constant, unchanging amount of airflow from start to finish. This provides a stable baseline so reviewers can measure the exact thermal output of a component without the cooling system actively fighting to change the results mid-test.
Neutralizing Aggressive Factory Settings
Different manufacturers program their hardware with different priorities. One graphics card manufacturer might prioritize silence, setting a relaxed fan curve that allows the card to run hot. Another manufacturer might use the exact same physical heatsink but program an aggressive, loud fan curve to keep temperatures low.
If a reviewer leaves the fans on their automatic settings, the louder card will appear to have a better cooling design simply because the fans are spinning faster. Locking the fans to a fixed percentage forces both products to operate under identical rules, revealing which manufacturer actually built the better cooler rather than which one set the most aggressive software profile.
Isolating Heatsink and Case Design
Thermal benchmarking is often about testing the physical metal of a heatsink, the quality of thermal paste, or the airflow layout of a PC case.
- Testing Thermal Paste: When comparing thermal pastes, the cooler and fan must behave identically every single time. A fixed fan speed guarantees that any temperature difference is solely the result of the paste.
- Testing PC Cases: When testing a computer case, locking the internal CPU and GPU fans ensures those components don't automatically ramp up to compensate for a case with poor airflow. If a case has bad ventilation, locked component fans will directly result in higher temperatures, clearly exposing the case's flaws.
- Testing Heatsinks: When testing a specific GPU or CPU cooler, locking the fan speed demonstrates how efficiently the heat pipes and radiator fins dissipate heat at a specific airflow level.
Stabilizing Modern Boost Clocks
Modern CPUs and GPUs use boosting algorithms that automatically increase their clock speeds—and consequently their heat output—if they detect available thermal headroom. If a fan is left on "Auto," it might suddenly ramp up, cool the chip down by a few degrees, and trigger the chip to boost higher and draw more power. This creates a chaotic loop of fluctuating power draw and changing fan speeds. Locking the fan speed stabilizes the thermal environment, leading to predictable power consumption and consistent benchmark scores.
Ensuring Long-Term Repeatability
Hardware reviewers often compare a brand-new product against data collected months or even years prior. For historical data to remain valid, the testing methodology must be strictly controlled. Firmware updates and driver changes can silently alter how "Auto" fan curves behave over time. By manually overriding the software and locking fans to a set percentage, reviewers guarantee that a test conducted today is performed under the exact same mechanical conditions as a test conducted a year ago.