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CPU Fan, Up or Down?

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May 11, 2001 7:58:13 PM

I know its a silly question but here it is. I put a new HS/Fan on and had to assemble it myself. The diagram shows it with the fan blowing up, away from HS, which I imagin it would cause it to suck air in from below. Is this correct, or should I flip it over so it is blowing down on the HS.



Crap, all the good ones are already taken.

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Anonymous
a b à CPUs
May 11, 2001 8:13:24 PM

The way it comes is the way u use it
sucking air out

--call it what you wish, with this machine I can make mercury flow in 3 directions at once--
May 11, 2001 8:20:36 PM

The fan blows toward the cpu on most HSF so that is what i would do. You can try it both ways and see if it makes a difffernce. What kind of hsf is it?
mbaha

“Build your own you will love it more”
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May 11, 2001 8:20:57 PM

You want the fan blowing up, away from the heatsink. The diagram is correct.
May 11, 2001 8:25:11 PM

Actually the way you use it is up to you, Neither way is wrong. The best thing to do is try it both ways and use which way gives the lower temperatures. I have found that blowing towards the CPU usually gives the best results.

Cya


<font color=red>There are only 2 types of hard drives. Ones that have crashed and ones that are about to.</font color=red>
May 11, 2001 8:36:19 PM

The fan is supposed to blow down into the heatsink fins.

I know this because every CPU HSF I've had has the fans turned that way. The job of the fan is to force warm air out of the heatsink fins as they dissipate heat; a fan causes more pressure (taking pressure as an absolute value, not as positive or negative) on its outtake side than on its intake side. You can confirm this yourself using a common desk fan or the like; there's probably some crazy physics to explain why this is so, but I do not know the details...

Kelledin

bash-2.04$ kill -9 1
init: Just what do you think you're doing, Dave?
May 11, 2001 9:18:43 PM

Thanks all for the responses. I will try it the other way and see if it helps and if it doesnt then Ill just put it back. The other fan I had blew air down thats why i got confused, I didnt know they made them different. It seems to me from the posts that it is a "your personal preference" type thing with what works best in mind. Once again thank you.



Crap, all the good ones are already taken.
May 11, 2001 9:30:21 PM

air flow is air flow
May 12, 2001 1:03:48 AM

no, it's not as simple as that. Read the obove explanation about intake and outtake. That was a very good explanation. The fan is meant to blow on the fins forcing the heat out so they can absorb more from the bottom plate closes to the CPU.

Beer is the devil's piss.
May 12, 2001 1:08:43 AM

Well honestly you'll probably only see about 1-2 degrees (C) difference. Personally I prefer down blowing as my intakes fans are in the back directly behind the cpu blowing cool air into the cpu fan. But as I said airflow is airflow.
May 12, 2001 3:39:05 AM

To tell you the truth, there's a chance that if you shroud the heatsink, and make sure the majority of the airflow is 'inline' with the cpu, you'll get lower temps on your core. But if you use duct tape to make your shroud, you'll see all the nifty dust and dirt piling up on the outter edges of the heatsink, which makes it less effective overall.

I'd blow down on the sink, until you're got the time and are ready to modify it...
May 12, 2001 3:40:52 AM

Well I actually tried it with the fan blowing down into the fins. I however changed it back to blowing up, sucking air in from the bottom. The reason being is this; with fan blowing down I had a temp of 59C under load, and with fan blowing up my temp was 55C under load. I guess I just cant get it any cooler. I had same temps with HS/Fan that came with it so I bought a new HS/Fan, (Alpha PAL6035) and Artic Silver 2 and I gt about the amse temps. Well I am about 4C less with new HS/Fan but still 55C wow, Thats under gameing load. I get 51C when just sitting there not doing anything. 1.33GHz

Crap, all the good ones are already taken.
May 12, 2001 12:47:26 PM

Man, I was so worried about my cpu hitting 48C at load that I put 4 case fans in(including a big a$$ 12 inch mo fo on the back), I have a server tower and i took the power supply out from the middle(upper middle) and cut a hole in the top and put it there, then placed the big fan taking out right above the mobo(where the chip is) I have a small regular case fan pulling in in the front bottom, and another small one RIGHT above the hsf pulling to the big mama jama, but the COOLEST pardon the pun, fan of all is a honking sunon i mounted right below the hsf blowing on it, so ive got a sunon blowing from below through the hsf and a case fan pulling that nasty hot air up and out the back.

btw, my hs is the thermo engine and its got a delta on it.

the grand result....

91 farenheight 31C idle

and 104 farenheight 40C under load, with maybe a rare peak to 43c.

the delta is blowing on the heatsink.

oh, the cpu is 1.33@1.55 at stock voltage.

~Matisaro~
"Friends don't let friends buy Pentiums"
~Tbird1.3@1.55~
May 12, 2001 1:12:55 PM

It does make a difference which way the airflow goes. In the case of a PC case it really matters on where the hot air is pushed to. The fan will push or draw air through the fins, the important part is where the heated air goes, which ever way sends the heat out of the case is the best way, recirculating hot air through the fins is the biggest problem.

Now if you think you've got issues. Pixar (the makers of Toy Story) have just purchased a 2000 CPU UltraSPARC III rendering farm. They could melt icecaps with that sort of heat.

<font color=blue> The Revolution starts here... as soon as I finish my coffee </font color=blue> :eek: 
May 12, 2001 4:12:24 PM

It all depends on the way the heatsink was desinged. I have seen both, fans blowing upwards and fans blowing down. Most of the high peformance fans do blow downwards however. More importanly is that you need to look at the airflow in the whole system as a whole, not just one singular component. For instance, on one of my comuters, the cpu is mounted towards the rear of the case. I have a delta fop 32 with a downward blowing fan. So, I installed my case fans so the the rear fan is blowing in giving the CPU fan a constant supply of cold air to draw from. This leaves the front mounted fan blowing outward to exhaust the hot air outside. Remember to look at you cooling system as a whole and you will be much better off. Just installing more fans is not always the best answer. If not properly positioned they may actually be opposing each other and not helping at all.

A little bit of knowledge is a dangerous thing!
May 12, 2001 5:17:47 PM

~ Just installing more fans is not always the best answer. If not properly positioned they may actually be opposing each other and not helping at all. ~

Listen to this man, he is on the money.


<font color=blue> The Revolution starts here... as soon as I finish my coffee </font color=blue> :eek: 
May 13, 2001 5:38:51 AM

Ok ill let ya know what I got. I have a Enlight 7237 case with a 80mm fan in bottom front panal, it is a intake. I have a Alpha PAL6035 with same fan as FOP-32, blowing away from cpu. I have a 80mm exhaust fan in rear of case right behind the cpu. And I have the PS fan with intake above cpu and in front of PS also. I am starting to think that my sensors are wrong since it says my case is 38C, I find that unlikly. Plus BIOS always reads a few degrees C lower than the PC alert program. How can I tell how accurate it is? I'm not going to do any "Crazy" mods to case or anything.

Crap, all the good ones are already taken.
May 13, 2001 5:59:42 AM

I'm no case cooling guru, but shouldn't anyone that posts cpu temps also post their ambient temp? I think it has a pretty big impact on the cpu temperature. For me, I have an 850 T-Bird at stock core voltage and 100fsb. Swiftech MC370-0A heatsink, 2x80mm High Speed Sunon fans (1 front intake, 1 rear exhaust in a generic mid-tower). At 27°C (my apartment norm...pretty darn hot...), my cpu is at 41°C, while right now, my ambient temp is around 22-23°C, my cpu temp is now at 36.9°C. Ambient temp makes a big difference, I think... :eek: 

As for my temperature readings, this was my "methodology":
I removed the heatsink and look under it, being able to see when the CPU core location is by the AS2 thermal compound. I purchased a Compunurse thermistor and taped the probe so it is as close to the core as possible (note: it's <b>not on it!</b>). BTW, the tape is on the side of the heatsink, not under it. I have no clue what kind of tape I used. It's yellow, pretty sticky...and definitely not scotch tape.

As for my ambient, I have to resort to taking out my probe and letting it hang somewhere in open air, until I can get a room thermometer.

I hope that's helpful (and a legitimate explanation) of how I test my temps.

<i>OC...unless your computer's cheezy (is that a good rhyme?)</i> :eek: 
May 13, 2001 6:11:09 AM

Before I suggest anything first tell me what the case temperature is with the side of the case removed. If it still reports at or around 38 degrees than there is nothing much else you can do. if removing the sides causes a big difference then I will suggest some changes.

A little bit of knowledge is a dangerous thing!
May 13, 2001 1:42:23 PM

My ambient temp before the mod was always 80-90 farenheight
now it is never above 76 farenheight. The KT7A RAID mobo's cpu thermal sensor is in the center of the socket right under the cpu.

~Matisaro~
"Friends don't let friends buy Pentiums"
~Tbird1.3@1.55~
Anonymous
a b à CPUs
May 13, 2001 5:14:26 PM

I've tried it both ways. The way the diagram shows the airflow to suck the air from the bottom works the best. It ran 1-2 degrees celsius cooler sucking the air air. This is especially true with copper since it spreads heat better the aluminum it does not dissipate heat better than aluminum, so to increase the efficiency it should be used as it was designed to. However, you don't want it to disturb the airflow of the case, so make sure that you're getting good exhaust out of the case. You don't want to create an absence of air in the case, nor do you want the air circulating to long. Best thing to do like some of the other posts say is phuck around with it until you get the best cooling.
May 14, 2001 12:26:54 AM

I experience the same. I have a 1,33 and when doing nothing it goes up to 51.

According to a review on Socket A on this site I should have better results. It's probably because I have a 1.33.
May 14, 2001 12:57:07 AM

Ok my room temp is 24C or 75F, and when I take the case cover off it still reads about 38C. However when it first boots up my cpu reads like 35C and case reads like 30C, but they go up very fast and then just stop at 53-55C and 38C




Crap, all the good ones are already taken.
May 14, 2001 5:29:59 AM

Try swithcing the order of the case fans and see if that helps, it does appear that your motheboard monitor is reading approx 6 degrees celsius to high. with this in mind you are almost were you should be. If you can get a few more degrees cooler you should be set.

A little bit of knowledge is a dangerous thing!
May 19, 2001 6:38:48 AM

My motherboard is away for repairs now, so I can't test just yet. But I sanded the little bumps off of the HS so mayby that will bring me down some too. Lets see as soon as I get my stinking MB back.

Crap, all the good ones are already taken.
!