Case ventilation and airflow: Cooling the PC properly

In short: Good airflow brings cool air to the components and carries warm air out of the case; the number and direction of fans matter more than their quantity.

In more detail: Processor and graphics card produce heat that their coolers release into the case air. If warm air accumulates, temperatures rise, fans spin louder and components throttle down (thermal throttling). Airflow describes the path of air through the case.

In Depth

The basic principle

Warm air rises. So you draw in cool air at the front and bottom and let warm air out at the back and top. Typical: two to three front fans as intake, one rear fan and one to two top fans as exhaust. The case is then in slight positive pressure when more air goes in than out, which draws less dust through gaps.

Positive and negative pressure

• Positive pressure (more intake): dust mainly comes through the filters of the front fans, which can be cleaned.
• Negative pressure (more exhaust): draws air also through gaps and can pull in more dust. It is best kept balanced with slight positive pressure. Dust filters on all intake openings help.

Fan sizes and quality

Large fans (140 mm) move a lot of air at lower speed and are quieter than small ones (80 or 92 mm). Sleeve bearings are cheap, magnetic or fluid bearings last longer. Fans with PWM (4-pin) regulate speed by temperature. For radiators and filters, fans with static pressure are better; for free case openings, those with high airflow.

In practice

• Tidy cables so they do not block the air path.
• Remove dust every few months (compressed air or brush, hold the fan still).
• Watch temperatures with tools such as HWMonitor or sensors; under load up to about 80 °C is normal for CPUs.
• Adjust fan curves in the BIOS to balance noise and temperature.
• Cases with a mesh front are cooler than those with a closed glass front.

See also: Cooling and thermal paste, TDP and thermal throttling, Power supply and 80 Plus