Should my computer fans be sucking or blowing?

Updated: 01/24/2018 by Computer Hope

Heat sink and CPU fan

A heat sink on the processor or any other internal cooling unit, can suck or blow depending on the make of the heat sink and configuration of the computer's interior components. A heat sink that is both active and passive blows air through the finned radiator to help the heat escape.

Case fans

Computer case fan airflow

Your chassis configuration determines whether or not the fans should be blowing or sucking. Computer cases that have only one fan in the back should always be blowing the hot air out. Another common configuration is to have the fan in the back with a fan in the front portion of the case sucking in air.

As can be seen in the picture, the computer case brings in cold air from the front of the case. Because it is always open and not constrained, and as the lighter hot air rises in the case, it is blown out the back. The important thing to remember is, when working with a computer that has more than one case fan, at least one should be sucking air in and one should be blowing air out. Having all fans blowing in with cool air would give the hot air no way to escape.


It may not be necessary to have a case fan in the back of the computer if the computer has a power supply with an intake fan that blows hot air out the back.

Related questions

Should fans mounted on the top of the case suck air in or blow air out?

Because hot air rises, we suggest that if you are building a case that has additional fans added on the top, those fans should be blowing hot air out of the case.

How should side case fans be mounted?

If you are building a case and mounting fans on the side of the case, we suggest that they be blowing air into the computer.