total numpty question

[Monkey boy 1]

On a pc case, does the fan suck air in or blow it out ?
Need to fit a new fan & wasn't too sure which way round it goes

[ThePassenger]

Short: Depends.

Long: Generally speaking if the fan is at the lower front of the case it's a sucker (brings cool air in). If it's midway or top rear it's a blower (vents heated air). Some clever sods design systems around negative pressure in the case (everything sucks, thus cold air is drawn in from the vents) or positive pressure (everything blows, hot air is blown out the vents).
Heatsink fans seem to be a personal preference, some like it pumping air down, some like it drawing cold air up. And finally side panel fans tend to blow, depositing addtional cold air to the HSF assembly and to the PCI/AGP/PCI-E card areas.

Edited by ThePassenger on Friday 8th June 17:01

[Monkey boy 1]

Right, clear as mud then


thanks anyway

[dilbert]

Monkey boy 1 said:

Right, clear as mud then


thanks anyway

Doesn't matter......

Make sure that there is a continuous path for the air, into and out of the box. Make sure that no two fans conflict.

[lazy_b]

ThePassenger said:

Short: Depends.

Long: Generally speaking if the fan is at the lower front of the case it's a sucker (brings cool air in). If it's midway or top rear it's a blower (vents heated air). Some clever sods design systems around negative pressure in the case (everything sucks, thus cold air is drawn in from the vents) or positive pressure (everything blows, hot air is blown out the vents).
Heatsink fans seem to be a personal preference, some like it pumping air down, some like it drawing cold air up. And finally side panel fans tend to blow, depositing addtional cold air to the HSF assembly and to the PCI/AGP/PCI-E card areas.

Edited by ThePassenger on Friday 8th June 17:01

Absolutely correct.

IIRC the original ATX specification relied solely on the PSU fan at the top/right (top = tower, right = desktop) of the case. The CPU was (is) located close to the PSU and relied on the airflow from inlets at the front of the case - through the PSU - for cooling.

With increased CPU (and graphics chip) power, separate fans are usually incorporated on the motherboard. Nevertheless, the rule-of-thumb stays the same - In at the Front, Out at the Back.

[ThePassenger]

Monkey boy 1 said:

Right, clear as mud then


thanks anyway

... Sorry, I thought that post was simple enough. In at front/bottom out at top/rear, it can't be made simpler than that. Unless your asking which way round the label goes??

[Monkey boy 1]

ThePassenger said:

Monkey boy 1 said:

Right, clear as mud then


thanks anyway

... Sorry, I thought that post was simple enough. In at front/bottom out at top/rear, it can't be made simpler than that. Unless your asking which way round the label goes??

It was clear, just that as you said it really doesn't make a difference how you put the fan in, as long as there is a clear path of fresh air going through the case.
Thanks again for the help all you out there in PH land

[TheKeyboardDemon]

To help, most fans have an arrow on the side showing which way the air will blow, some even have a second arrow to show what direction the fan will turn in.

[Monkey boy 1]

sussed that one out, Thanks

[TheKeyboardDemon]

It took me a while, I don't know how many times I took fans out and reinserted to get the blowing in the right direction. ho hum...

[sadako]

Long story short, put them to blow into the case if you are fitting it at the bottom of the case, and put it to suck out of the case if you are fitting it at the top of the case.