As processor speeds have hiked in past few years, manufacturers have started using fan with slow, quiet fans. Today’s processors differ in power consumption from less than 30W to more than 100W, with proportionate differences in heat production. At the bottom of that range about any decent CPU cooler can do the job with minimal noise, including the stock CPU coolers bundled with retail-boxed processors or cheap third-party units. In the middle of the range standard CPU coolers start to generate invasive noise levels, though specialty silent CPU coolers can cool a midrange processor with little noise. At the top of the range, even the quietest fan-based CPU coolers generate noticeable noise.

For a slow processor, try the stock fan unit supplied with the retail-boxed processor. If it generates too much noise, install an inline resistor to cut-down the voltage supplied to the fan, which in turn reduces the fan speed and noise.

For a midrange or fast processor, there are various options. Some of the CPU coolers mixed with Intel Pentium 4 processors are sensibly quiet in stock form, and can be quieted further while providing enough cooling by using an inline resistor to reduce the supply voltage to 7V. However, Intel uses various CPU cooler models and changes them unnoticeably.

To reduce the noise for any processor, install one of the Thermalright or Zalman units. Especially, with slow and midrange processors, Zalman “flower” coolers can be run in silent mode, which entirely takes off CPU cooler noise.