# CPU Fan Sucking or Blowing?



## reload (Jun 21, 2005)

When you install your cpu fan onto your heatsink is it suppose to suck air from the cpu or blow air down to keep your cpu from overheating? Thanks for any info!
Reload
[email protected]


----------



## Tumbleweed36 (May 14, 2005)

Hi,

That is a tough one. It kind of depends upon who you are talking to be quite honest. The vast majority of techs and CPU manufacturer's recommend that the heatsink fan blow DOWN on the Heatsink and CPU. I am a proponent of that and have found it to be very successful.

However, in fairness to the other position, UncleMacro on this forum has made a compelling case for the other position in a recent idea exchange on the forum. He feels that if he can suck out the hot air from the top and have that air travel into a tunnel (he hand made the tunnel) that expells it from the computer, that this is the best solution.

Since most of us don't have the tunnel or the means to manufacture one, I would suggest that you let the fan blow down on the heatsink and CPU as per manufacturer's recommendation, but I am sure you will get other opinions.


----------



## V0lt (Sep 14, 2002)

I would second that. UncleMacro's idea is compelling, and I have seen cases that do have this feature, but it just makes sense to have it blow downwards, as it displaces the air closest to the core the most vs. taking it from the sides and just expelling it.


----------



## UncleMacro (Jan 26, 2005)

You'd be surprised how a simple question like this can start a huge discussion. (Eh, Tumbleweed? :winking But if you're not doing anything unusual then you should just have the fan blow down on the heatsink. Some heatsinks work almost the same whether the fan sucks or blows whereas others run quite a lot cooler while blowing.


----------



## TheUnlimited (Dec 12, 2005)

I've had experiences with non-ducted fans going both ways (both accidental, too). If you can rig up something special like UncleMacro, that's awesome. But from my experience with a Thermaltake Spark 7, it kept cooler blowing down. Similarly, with a Vantec Aeroflow 2, the CPU temps dropped over 5 degrees Celcius when I put the fan blowing down.


----------



## reload (Jun 21, 2005)

Why I asked this question was because my ASUS PC PROBE came on and warned me that the cpu had gone beyond it's threshold which is set at default 54C/129F. The temperature showed 88C\190F in my asus probe. So I shut down my pc and turned it back on an hour later. So right now it's at cpu temperature 44C\111F. My cpu fan is blowing down and the speed of the fan is 4963 and sometimes up to 5000. I'm using a cpu acc xp-90C HSINK with a Vantec Tornado 92mm. So this is the first time that ever happened!


----------



## UncleMacro (Jan 26, 2005)

If you've got a sudden temperature rise like that without any hardware changes then I'd check to make sure the fan is spinning full speed. Another much less likely cause could be some kind of BIOS problem which set the CPU voltage too high. Heatsink grease creepage and dust can also raise the temperature but those changes are gradual rather than sudden. But if the temperature rise was that much (assuming it's not just a software problem misreading the temperature) then it's probably the fan. An XP-90 is a high capacity heatsink and the temp wouldn't really go up that much unless there's a major change in the amount of air flowing.


----------



## Ralck (Dec 10, 2004)

Another reason for increases in heat could be dust. As Uncle Marco said, it does sound like the case of a failing fan, but also get a can of compressed air and blow out your system while you have the side off.


----------



## reload (Jun 21, 2005)

Well, I'm sure I found out my problem at least hope so? The 2 front case fans couldn't get enought cool air because my tower dust filter was completely covered with a layer of dust. I just cleaned it 3 months ago and it was just full of dust. Also I removed my cpu fan which is blowing air down to my cpu. That was also covered with a layer of dust. I couldn't believe the amount of dust that I removed. So I changed the direction of air flow from my cpu to where it's blowing air away instead of sucking like before. I'll check my temperatures and see if it makes a big difference with my cpu fan blowing air away from my heat sink? If it doesn't I'll just have it sucking air like before! Right now my cpu is at 42C\105F and cpu fan speed at 4891. I checked my bios and I didn't notice any changes since UncleMarco helped me unlock my cpu and it's running at the right speed 3400MHz Thanks again everyone. I really apprecitate all the replys you people are a great help!
Bob
************************


----------



## Tumbleweed36 (May 14, 2005)

UncleMacro said:


> You'd be surprised how a simple question like this can start a huge discussion. (Eh, Tumbleweed? :winking


Hey Uncle,

You do have to admit that I was fair with your position and gave it equal space, eh???????:4-dontkno :4-dontkno 

We are happy that this one is at least working again, so have a great evening all you guys.


----------



## UncleMacro (Jan 26, 2005)

Tumbleweed36 said:


> You do have to admit that I was fair with your position and gave it equal space, eh???????


Yea. When I saw the suck/blow question, I cringed a bit and thought (with a smile) "Oh no. Not again!" and then saw you bringing up my duct stuff. Personally, I don't suggest that people use the suck orientation unless they've got a good reason to. Going with the design and blowing makes sense. People just seem to get their knickers in a twist over a few degrees C. People's room temperature increases more than that in the summer and yet their CPUs just keep chugging along just fine.

From the looks of the heatpipes on the XP-90 I would think it's one of those heatsinks that isn't going to particularly care which way the air is flowing. Some of the newest heatsinks have even eliminated any fin connections to the CPU and use only heatpipes to transfer the heat so the air direction wouldn't make much difference at all.


----------



## Ralck (Dec 10, 2004)

What might be interesting is to try a system of a duct bringing air from the front of the case to the CPU fan, blowing down on the heatsink. Then, a duct around the heatsink gathering the warm air and bringing it directly out the back of the case? Kind of like a form fitted wind tunnel in a sense.
You up to try that in your next build Uncle Marco and tell us how something like that would perform?


----------



## crazijoe (Oct 19, 2004)

Ralck said:


> What might be interesting is to try a system of a duct bringing air from the front of the case to the CPU fan, blowing down on the heatsink. Then, a duct around the heatsink gathering the warm air and bringing it directly out the back of the case? Kind of like a form fitted wind tunnel in a sense.
> You up to try that in your next build Uncle Marco and tell us how something like that would perform?


That's pretty much how the BTX cases work.

http://www.anandtech.com/casecooling/showdoc.aspx?i=2276&p=6


----------



## reload (Jun 21, 2005)

Well Guys I have my cpu fan where it's sucking air to the cpu and it's decreased my temperature by 5 degrees! My pc has been on for over an hour and the temperature is staying at 44C/111F. I'll just leave it the way it's suppose to be and just monitor it with my asus probe. So I'm hoping it was just a dust filled screen that wasn't letting any cool air flow through? Mucho thanks for all your info. 
Bob,
************************


----------



## UncleMacro (Jan 26, 2005)

> That's pretty much how the BTX cases work.


Unfortunately, BTX cases exhaust their hot CPU air inside the case just like standard ATX. The CPU gets cool air coming in from the front but that warmed air then goes over the rest of the components. The main point of BTX seems to be to get average cooling while cutting back on fans. It looks like something to make OEMs happy by cutting costs rather than a good cooling solution. It seems to cool pretty well considering the minimum of fans but the CPU fan is in the front of the case so it will become more of a noise annoyance as CPU heat consumption rises.


----------



## -d- (Jun 18, 2006)

Am I the only one that laughed @ the title of the thread? Ha..ha...

Blowing will cool the CPU, sucking will just ventilate it better. That's my understanding of it. If the other way works fine for you, stick to it, and hopefully it stays the extra 5 degrees down!


----------



## Ralck (Dec 10, 2004)

Well, More what I was saying, is form fitting. A duct coming from the front to mount/seal on the top of the HSF, the fan blowing down on the cpu, and another duct fitting around the side of the HSF sealing around it and 'catching' the hot air, and bringing it directly out of the case through the back.


----------

