An exhaust fan takes the air from the case and pushes it out into the surroundings. So wouldn’t that very act of removing air from the case create lower pressure in the case, causing air from the outside to get sucked in, regardless of the existence of intake fans?
In: Technology
Yes, it does. However in order to help keep the inside of the PC clean, filters are fairly common on intake fans in order to keep as much dust, hair, etc from going in.
If you have no intake fans, any slight air crack becomes an intake from the negative pressure, and there’s no filter on that. So dust will get in easily.
If you have intake fans – preferably more than you have exhaust fans – the pressure becomes positive, and air blows OUT those cracks. With a filter on the intake fans, the inside keeps a lot cleaner.
It aids and helps control airflow. You don’t just want air to come in and then get shoved out. You need to it to flow in certain paths to help cool specific components. If you push it in at certain points and then pull it out at others it creates specific flow paths. If all you do is exhaust or intake, the air moves to escape from all the case gaps instead of the desired in/out spots.
The intake and exhaust setup also reduces the strain on the fan motors, which reduces the chances of them failing.
One big reason that you want an intake fan is to ensure that the air coming into the PC is coming from a particular direction.
If you just had rear/top exhaust fans, and had openings for air to come in from the front, bottom, and sides, you don’t really know where the air is coming from. The air the fans are pushing out could be passing through the case in such a way that they don’t really cool any of the components.
By adding intake fans, you can better control the path the air is taking through the case, which means better cooling than just passive air intake.
> causing air from the outside to get sucked in,
That’s called a low pressure configuration, and basically turns your PC into a dust trap. The air will get sucked in through connectors, random vents, PCIE slot covers, etc., bypassing most filters. If your case has decent air filters, you want positive pressure (more intake fan capacity than exhaust) so air is filtered going in, and all the random gaps have clean air going out instead of dusty air going in.
Airflow. If you only had exhaust fans in the back, there will be intake from anywhere air can come in. This means there is much less airflow in the font of the case, resulting in pockets of hot air. Adding intake ensures a path of fresh air throughout the entire case.
Intake fans create positive pressure in the case, drawing in air from where you want it. This can be over dust filters, for example. They aren’t strictly needed but tend to keep the case cleaner and cooler.
You kinda want the entire case to act as an exhaust fan, by using more intake than exhaust fans. If you only have exhaust fans, every crack becomes a vacuum intake and makes it easy for dust to get sucked in.
But, if you have more flow inwards (*going through filters)* then instead of sucking through all the cracks it will be blowing lightly and keep dust from getting inside.
Others have stated the reason quite well, but I’ll add this thought. You can push air where you want it, but you cannot pull air anywhere.
In the case of PC components, you must push air past components that need cooling. You cannot pull air past them and expect good results.
They don’t. There are millions and millions of Dell Optiplex etc. PCs with one CPU fan and one 92mm rear exhaust, or in the case of SFF PCs, just one combined CPU/exhaust fan (+the PSU as exhaust). It’s no major problem with a ~70W TDP processor, and a handful of Watts from the other components, it’s fine. (They also use beefier fans than most enthusiast PCs).
The real reason is that PC fans produce very little pressure difference, you get a little more flow with one in, one out vs two out.
Other responses are correct but they haven’t mentioned how air likes to form vortices. With no front intake fans, GPU and CPU air intake would become negatively pressurised, meaning some hot air exhausted would rush there making your pc parts unable to cool themselves. Your case would become an oven.
Intake fans are needed to create positive pressure in places so that hot air doesn’t recycle itself in the case. This also happens outside of the case, so I advise using some natural barriers to ensure this doesnt happen. Such as keeping the PC exhaust air seperated with something like a monitor.
Latest Answers