Howdy all!
Did a quick search to find a similar topic, but one was not immediately apparent, so I thought I'd raise the question - should a fan blow air onto or suck air from the CPU?
I recently upgraded my CPU Cooler from the stock Intel P4 HSF to the Thermalright SI-120 fitted with a 120mm Panaflo fan. Currently I have a 120mm Thermaltake at the front sucking air in (at the bottom), another at the back top sucking air out, and an 80mm on the side blowing air over the CPU (which blows onto the new HSF). Works great overall, dropped temps by about (on average) 8-10°C.
So here lies the question (and I could try it, but I think it is an interesting topic) - should I have the side fan blowing onto the Panaflo, and that blowing onto the CPU; the side fan sucking out and the Panaflo blowing onto the CPU; or vice-versa on both those options?
Bearing in mind that the SI-120 has about 2-3cm between the CPU mounting plate and the heatsink fins (heat passed by 5 heat pipes). Does the Panaflo then blow the hot air from the fins onto the CPU mount?
Any suggestions/comments welcome......

No takers? Anyone?.......Bueller? ....Bueller?

Generally, a computers fans are set up as a 'pass through' type of deal. Theres a fan in front (sometimes) that sucks cool air into the computer, and one or more in back blowing hot air out. As long as the air flows nicely through the case without any fans cancelling (two of them blowing or sucking from the same area--instead of one blowing and one sucking) most anything you can think up will probably work. In my opinion, air should be blown on to the cpu heatsink instead of sucked from it because blowing removes hot air and in turn provides cool air, as sucking would just remove the hot air and not provide the cpu with its much needed cold air.

The 120mm fans I would mount so that they are sucking air away from the base/cpu, and cooling the bottom of the heatsink, and another on top sucking hot air away.

About the 80mm fan on the side, I personally would have it mounted facing the back of the computer (or in that general direction), sucking hot air away from the cpu, and exhausting the hot air out the rear.

Thats just how I'd do it.

-Nick

The side fan was introduced, as I understand it, because of the high heat of Pentium 4 processors. The purpose is to blow cooler outside air directly onto the processor. The fans are designed so that they usually line up directly with the processor. In fact, an Antec case I recently used had an extendable sleeve to take it right down to the processor. It would be fighting the process to have either the side fan or the processor fan blowing away from the processor. My main computer has an AMD processor but the case still has the side fan, though it does not line up exactly with the processor.

Most cases now have side fans, with the exceptions being the larger system manufacturers like Dell, HP, Emachaines etc. Actually, HP makes (or used to make) a hard plastic "port" that went from the cpu fan to the exhaust fan on the back of the case. It actually worked very well. They (different manufacturers) make "shutes" or "ducts" that are flexible and help to concentrate on removing heat away from a certain area (cpu's, vga cards etc.)

I've also heard/been told that as a rule of thumb, fans should be in odd numbers, and with with larger number being exhaust (like 3 fans, 1 intake 2 exhaust/5 fans 2 intake 3 exhaust), so that there is more heat being removed than room temperature air being drawn in. This specially stands true for computers near heating vents, or small warm rooms (laundry room w/dryer that heats up the room), as they'll suck in the warmer air raising the ambient case temp.

Something that's usually overlooked is the use of a filter on intake fans (yes, myself included in that). Intake fans will not ony suck in cool air, but also suck in the dust and whatnot in the room. We all know that dust is bad for cooling fans, specially on the cpu cooling fan itself.

My usual ordeal is.

I have a fan blowing right ontop of the CPu heatsinks. one fan blowing out exhaust in rear, one fan in the front to suck in cool air.

That way, there is a consistant "flow" of air from front to back. The side panel usually has holes or some screen that fresh air can come in as well. I rarely put a fan directly on there. so far, no probs.

Oh, and don't forget, the psu fan

On all the heatsink setups I've seen with a built-in fan, the fan blows onto the heatsink. The rule of thumb for case fans is to draw air from the bottom front, and, because heat rises, exhause out the top rear.

My dad's HP has a P4 with no side fan, no duct (as of when I removed it and flipped the case fan to blow out the back ), and a fan/heatsink combo, and it's been doing fine running all day.

Sweet! Thanks for the help. I guess that means my current setup is OK. I have the fron sucking from the bottom; the rear blowing out the top; the side sucking straight onto the HSF, which in turn blows directly onto the heatsink. On idle it sits at about 36-37°C (when the room isn't too hot) and at full tilt (on-lin BF2 at HIGH 1024-768) running about 53-55°C. Well it doesn't go over 60°C any more either way!