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Air cooling: Suck or Blow ?

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Mar 24, 2001
I have read many discussions about the pros and cons of fans sucking or blowing. Thought I would share my own experience.

My system is setup so:
Asus A7V133/Tbird 1.2@ ~1.4 /256 Mb PC133 CAS3@CAS2

I originally used a Vantec/Delta BL to cool the bird. I managed to get a rock solid system @ 135 MHz with default voltage.CPU temp under full load is ~50-51C. I can push the FSB a bit further to roughly 137 MHz, but Windoze would eventually freeze on me, even if I increased voltage to the max (1.85V),although temp did not go above 53-54C. So ,I thought, must be the cheap generic RAM that hold me back.

Then yesterday,I switched to a PAL6035/Delta BL,with the fan set to suck air from the HS as per instruction. The first thing I noticed is the noise. It's MUCH LESS intrusive although the fan is the same, probably because of less turbulence between the HS fins. I cranked the voltage to the max, set the fsb to 137, crossed my fingers and boot into windows. Opened hardware monitor, checked the temp. OMG, 49C at idle! Must have applied that AS wrong. But too lazy to dismantle everything and redo it, so just left it as is :p Fired up Prime95 torture test, opened SSandra for some memory benchmarch at the same time, bracing myself for the CRASH. Took a peek at the temp, it has zoomed up to 55-56C! But still no crash ??! Went to bed,left Prime95 running, expecting to see a meltdown this morning :p
Turned on the screen. Prime95 is still going strong with no hiccup. Did some more benchmark, surfing, downloading a movie,... the sonovagun just woudn't quit! The temp has stabized at 55C for a while now.

So,from what I can deduce so far, a low CPU temp doesn't necessarily mean a stable system. If the fan is pushing all the heat from the core onto the adjacent chipsets, ram,transistors,etc, that could circumvent a successful overclocking. In my case, it means I can probably o/c more at lower voltage if I take the time to do it right : reapply AS and install some ducting to get the exhaust air away from the core.

That's a project to consider :)
Up to a certain fan speed, your experience is valid. Beyond a certain speed, the air washing out of the base of the heatink will aid in cooling the memory, northbridge, vcore regulators and PLL IC. My understanding of the 6035 is that it was designed to suck air out instead of blow it in.

Up to a certain fan speed, your experience is valid. Beyond a certain speed, the air washing out of the base of the heatink will aid in cooling the memory, northbridge, vcore regulators

Could be,but you must have enough room inside the case and good crossflow and/or ducting to move all that hot air out of the case. Otherwise, no cooling is possible.
Absolutely. For overclocking, it seems that a minimum ventilation system to shoot for is an 80mm fan blowing fresh air in and an 80mm fan drawing the displaced, warm air out. A pair of 92mm are even better, but that involves enlarging the case openings. It is time well spent. If you are striving to hold it to just those two fans, you can go one further, like I did and put a 120mm blowing in and a 92mm sucking out. In the conventional mid-tower, with its two add-on fan holes, if your HSF is a sucking type, given its proximity to the one case opening, it would be advantageous to put the fan drawing the air out in that spot and blow air in from the one in the front of the case. If your HSF is the kind that blows air down into the HS, then you are better off with the rear fan blowing cool air in, right above the HSF and the front fan extracting the warmed air. Forget the tenet about warm air rising. That only applies in systems with no fans. As soon as you add active airflow, it overcomes the tendency for warm air to rise, since simple convective airflow is very subtle and easily overpowered.

Last report b4 signing out: Played a movie at the same time as listening to mp3,while Prime95 continued flawlessly in the background, and still no crash !! Temp hasn't changed either,keeps at 55C.
Think I'll try that 139 fsb...:-D
I agree with Hoot on this. The decision of weather the fan should suck or blow is determined by the placement of your case fans and by how the airflow in the case works. You can mess up the airflow inside a case with a HSF.

For example I have an Enlight mid tower case with a Sanyo Denki 92mm 55cfm blowing in the bottom front, Panaflow 80mm 47cfm blowing out the back right next to the cpu. The cpu fan and the 80mm exaust sit at right angles to eachother. If I put a HSF with the fan blowing they fight eachother and cooling suffers, I tested this with a FOP38. The HSF I use in the case is a hedgehog with the Delta jet sucking. With this setup prime 95 will get the TBird @ 1350 up to the high 30's. In game play low to mid 30's, idle mid 20's. In testing with the fan blowing on the hedgehog the temps went up. I know the hedgehog has gotten a lot of mixed reviews but I suspect that this has to do with poor quality control on the way the fins are attached to the base. I happen to have a good one.
I prefer one blow, one suck

I have a Duron 650 which isn't currently overclocked.
I have an exhaust fan in the PSU.
I also have a second 80mm with the ATX Power thing

If I use the 2nd one to BLOW, it idles at 24C and goes up to 32C under load
If it SUCK, I get it idling at 30C and at 36C under load.
for case cooling id blow in the front and suck in the back-but for a cpu i prefer the suck method-dont even make a joke with that-u know what i mean
Each system is totally different & you can switch the way airflows. This is how I have my system setup. I have a full tower case. I setup the case to draw air in the front & side panels & exhuast through the rear. Have 69cfm 120mm blowhole Paniflo front bottom, Vantec 13 cfm HD Heatsink Combo, Two 42cfm 92mm Paniflo on rheostat supplying air on the side panel, 47cfm 80mm Paniflo exhausting mid way rear & a 85 cfm 120mm Paniflo exhausting at rear back top. Blue Orb on the GTS with a Buss PCI Fan card. I also replaced the cheap ASUS chipset fan with a 7cfm Sunon. My Enermax P/S helps a little.

As you can see I am fan crazy. My room temp usually is between 76-80*F & my system runs a steady 41*C under load monitoring with Asus Probe program. If my room temp is 70*F or less I hang around 36*C. The loudest fan in the case is the Swiftech Delta 69cfm 80mm fan. I run it all the time on low speed. I hate the noise but I have tried different combos of fans even double stacking them & the Detla still beats them all.
I have noticed that even with the side of my case open I still get differences in cpu temps depending on what direction my fans are blowing. I have a Enermalkaix (don't know how to spell it) power supply with two fans on it. One of the fans sits about three or four inches form the top of my HSF on my cpu. When it came form the factory it was blowing down onto the cpu. My immediate thoughts were Wow, it must be blowing the hot air form the power supply and form the top of my case down onto my cpu!!! That no good young grasshopper. So I did a no no and opened up my power supply and switched it around.

(power supply capacitors can still hold a charge after you turn the PS off so keep this in mind, dremel too no go there LOL)

After making the change I had a 5^C lower cpu reading. It's amazing what fans do In a case. As I've learned you have to play around with them and test different setups. There's no fast and easy fix to anything, patience and time will prevail in the end and bring you the best results. Every case and setup is different. You should also play around with having the case open or closed. I just read a form today on that, to save you the reading we have reached the same conclusion. Test and Try all your possibilities and then use the best one.

Hope this helps. zoopa_man
When you had the fan blowing on the Alpha did you have the shroud on? I have noticed on the Pal 6035 and the Hedgehog if you leave the shroud on with the fan blowing the temps will be quite a bit higher then if you remove it. The opposite is true when the fan is sucking, best cooling is with the shroud on.
This is one of the alpha's designed with a shroud, where the fan is on the side and NOT the top, right? In a case like this, the fan sucking would be the same(basically) as the fan blowing, because of the shroud, and because of the fan being on the side. However, if the fan is on the top, and you have it sucking, basically no air will ever wash over the center of the heatsink. And where's the CPU core in-contact with the heatsink? That's right, the center. I think it depends on the positioning of the heatsink as well, in the case of alpha's anyway.
P!!!800@1GHZ CCO 1.7v

I'm blowin down on HS with PVC DUCT on sidepanel.

room @24c
idle @30c
load @36