Suck or Blow? Computer Case fans.

I am in the process of building a new computer for myself. The new machine will have fans galore spread throughout. Of course the CPU will have a fan, as will the chipset (it’s a 875 chipset and the first one that I have seen that has a heatsink and a fan), the video card will have a heatsink and fan too. The new case that I bought has, now I don’t remember exactly, 6 fans. I know that there are two at the back, one on top, one on the side and I think two at the front.

Should the fans all be sucking in or blowing out or a combination? I would guess that good air flow is probably the best choice, but I just don’t know.

Not that it should matter, but the motherboard is an ABIT IC7, the CPU is a P4 2.8 and the video card is a GeForce FX 5900, and I have a 500 watt power supply.

Doesn’t matter as long as the case has plenty of gaps to let the air in/out.

Common sense says the fan should move cold air if possible, so “blow” is better.

However, convention usually has a blower at the front of the case and a sucker at the rear.

Prefer blow to suck and filter most of the blowing fans.

You should aim for slight overpressure as the case won’t be airtight and overpressure will prevent dust from sneaking in through the cracks. Usually it seems that the front fans and the side fan are blowing while the top and back fans are sucking, minimal in-case restriction (keep your ide cables tidy) also helps. Also remember the fan(s) on your power supply, as these will be suckers.

Ideally, air would come in thru one corner, flow across everything, and exit the opposite corner. In the real world, you try to approximate that.

The power supply fan probably is blowing out. Any fans on the same side as it, nearby, should do the same.

A fan in the opposite corner (e.g., lower front) should then blow in. Ditto any fans in that vicinity.

Avoid situations such as an in-blowing fan near the hard drives blowing straight to the power supply, with no air circulating in the rest of the case.

Dust will get into your system regardless of pressure unless you are one of the very few who use filters. So be prepared to clean things out regularly.

Chip fans should blow air onto the chips. Case fans should impel at the bottom and expel at the top. This is because hot air rises. A slight overpressure is a good idea as np_complete says.

ftg is correct. Your power supply blows out the back of the case, thus, any fans on the back of the case should also blow out. Any fans in the front of the case should suck into the case. Any fans on the top of the case or on the side of the case should blow out. :slight_smile:

Thanks for the input. I’ve pretty much resigned myself to the fact that there is going to be a dust problem with this machine. Almost none of the ports on the motherboard align with the cut outs on the back of the case (mouse and keyboard do, LPT and everything else do not), and I had to remove that whole section.

Okay…not a professional opinion but one from experience. You should always match computer fans sucking in with those blowing out…

Depending on what your setup is… two fans in front of your case, sucking in, power supply and rear fan blowing out.

Others with side fans or top “blowhole” fans should also balance the CFM of the airflow as close as possible. Side panel fan blowing IN to the CPU, top case fun blowing OUT.

ALso… your case will run cooler with the side panels ON rather that with them off…better airflow that way.


"Dust will get into your system regardless of pressure unless you are one of the very few who use filters. So be prepared to clean things out regularly. "

You are probably already aware of this as a system builder, but for god’s sake never use a vacuum cleaner to remove crap from the works - the intense airflow builds up a respectable static charge tha can cripple your chips.

Or even:-

for an extreme solution.

If you’re pumping dirty air into the case using fans, I don’t think cracks in the case will be the source of your dust problem.

Actually I have a case cooling question myself.

Like Adam I’m putting together a new box at the moment. (you get that 2.8 P4 at Newegg btw?)

I have 2 80mm fans pulling in from front bottom, and two fans on the back, the psu itself (2 fans, sucks into the psu, then shoots out the back) and a case fan right under the psu. I’ll also have a fan on the video card, and one on the northbridge.

Anyway my question.

I have the case fan and the psu right up against each other (they are perpendicular) and they will be pulling air out of the case. What concerns me is it looks like the CPU will fall into place right in the middle of this maelstrom. Will I have to worry about the 2 fans “stealing” air from the CPU fan?

That’s true, and that’s why I recommended filtering his blowing fans.
My intent was to say that regardless of filtering, your computer will accumulate dust if you are sucking out more air then you are blowing in, this is due to small cracks in the case. You can elimate this problem by blowing in slightly more air then you suck out, as this will create a slight overpressure.

Considering that heat rises I would want the fans near the top to blow and the ones near the bottom to suck.
Similar to a house, fans on the top to expel the heat and air intakes near the ground to supply cooler air.