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CPU Fan Direction?

Last response: in Overclocking
December 30, 2005 3:02:54 PM

I have read quite a bit about this and it seems that there are a lot of different opinions on this

What do you recommend?

The CPU fan blowing towards or away from the heatsink?

More about : cpu fan direction

December 30, 2005 3:34:05 PM

The CPU fan should blow away from the heatsink to pull off excess heat. This also helps draw air across the cooling fins. If you have a rear fan (Like my 120mm exhaust fan), then the heat that the cooler is blowing away gets exhausted from the case.
January 1, 2006 12:46:28 PM

ditto, draw it away, and make sure you get a nice feed of clean air in there.
You want the coldest air closest to the cpu, so if it draws it bottom up, it'll work better than top down.
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January 2, 2006 5:33:56 PM

Have it blow into the sink to move air across all of the other components around the CPU (voltage regulators and such) that get a bit hot. Best way to find out for your current setup it to find its max overclock one way and the the other... At least thats how I do it.
January 2, 2006 5:41:42 PM

Aree, it should blow down to the processor letting sucking the case air down and over CPU circulating cooling chipset and mem also.
My LianLi PC60plus has an intake at rear, with a duct pulling in cool outside air and blowing it towards top of CPU fan, so it can then pull cool air down to the CPU.
So down it is.
January 2, 2006 5:42:13 PM

Are we in agreement now.
January 2, 2006 7:23:44 PM

Thats interesting. Thats the reverse of the way it is normally done. However, either will work, depending on your setup. on my rig, I have seperate VRM cooling, and the best thing I can do is pull the air away from the Chip to the rear exhaust fan.

(I believe most case circulate air in through the front and out the back. in that case you want to pull away, so you are not pulling hot air across the CPU).

The most important thing to remember is to move air from the coolest source you can get to the nearset exhaust you can get. On different boards/cases, you will get different results, though I still generally recommend pulling air away.
January 2, 2006 7:37:46 PM

I've seen benchmarks where in some cases it was better to have the fan suck air up from the CPU and others where it was better to blow down on the CPU... given the wide variety of results and the impact of case/heatsink designs, I'd attempt to measure the thermal characteristics with the fan mounted each way in some sort of controlled environment. That's what I did and I believe I saved an extra degree or two.

In this case I'm not sure there is a right answer, but I could be wrong.
January 2, 2006 7:44:54 PM

one thing to note, as rodney_ws stated, it that you are probably only going to save a degree or two by switching direction, which in most cases won't matter. It may play a little into OCing, depending in the rest of your setup.
January 2, 2006 7:50:33 PM

Wooooooooahhhhh. Guys. Stop. Do some research. The only time a CPU fan should blow air AWAY from a CPU is if you have another fan blowing air IN to the CPU (i.e., dual fan setup or a large case fan on the other side blowing air to it).

Air should ALWAYS be blown on to the heatsink in 99% of setups.

And the reverse way is never the standard setup. Every HSF solution on the market blows air on the heatsink.

Enthusiasts and what not are the ones who reverse it. I too have seen comparisons on both setups, from what I've <seen>, in a case w/ good air circulation, blowing air on the heatsink always resulted in the best solution.

January 2, 2006 8:16:09 PM

LOL some people crack me up. Your stock CPU fan will not work well you reverse the rotation. PLEASE notice the fan blades are CURVED NOT FLAT. This increases air volume so that lower rotation speed can be used. If you reverse direction alone you are hurting performance of the fan. CPU coolers always blow across the the heat sink to maximize coverage area. If you suck air away from the heat sink you lose a lot of area for reason that air always take the least line of resistance and will only pull through the outer most fins thus overheating issues.
January 2, 2006 9:03:37 PM

PC-60plus also has a 120mm fan blowing out rear, along with 80mm fan blowing duct to CPU for cool air.
Damn good cooling with LianLi PC-60plus case.
January 3, 2006 12:24:53 PM

Well, the 120mm CPU fan is now setup blowing thru the SI-120's HS, and it works like a charm :) 

The air from under the fins gets vented out of the case by two 120mm fans, top and rear (p-180)
a b à CPUs
a b K Overclocking
January 4, 2006 7:09:21 AM

Well, it's obvious that the first two guys to jump in know nothing about what they're talking about. Of course I have experience and training, yeh, I went to school for this stuff. Sorry!

OK, so the first problem with fans is that they pull air from the sides. That means a fan pulling air through the cooler works less effectively than a fan blowing in. Many of the guys here would say that a pulling fan has a larger "dead spot" in the center.

The second problem relates to the first, since the fan pulls air from the side the only part of the cooler getting good airflow in the "pull" configuration is the top. Not the bottom, where the CPU is. Bad idea.

It's such an incredibly bad idea that Intel, that's the company with all the funky engineers, specifies their own designs, all of which blow into a cooler rather than sucking out of it.

Now there was this cooler maker nobody remembers, I think they're still around, called Alpha. They thought pulling was better, but realized that fans pulled air from the sides. So they installed a shroud around the top half of the heatsink, so that air had to be pulled from the bottom. A funny thing happened: Even though the sinks were well designed and had a lot of surface area which optimized cooling, further optimization was found by REVIEW SITES who reversed the fan, to blow inward.

This fan shroud is really obvious to dumb mechanics, as many hot rods have been found to overheat when you remove the fan shroud. Yet as previously stated, you get better results from pushing air.

One reason it's better to push air of course is the directional thing previously mentioned. But another reason is...air doesn't pull very well. It's a gas. It likes to expand. Pulling just lowers the air pressure.

So it's easier to reach the base of the cooler from a push configuration not only because it's directional, but because the pressure also helps it reach the bottom of the cooler.

All this has been discuseed numerous times of course. And there's other reasons why push works better, such as the air being cooler as you move away from the board. But when it comes down to it, you could simply search the forums and find this all explained in more detail in old posts.

And then you'd also find guys who were really good at arguing for the pull configuration...loosing. These modern geeks are too soft for that kind of debate.
January 4, 2006 8:23:06 AM

Actually, I went to school for this stuff too (though I admit I focused more on IC design than high level system design), and I have received similar results from both directions in my setup.

After reading up on the subject, I will admit that I was initially wrong and that in most cases the air should be pushed, though as I said, I think that it depends a lot on your setup. (I have a 120 blowing across almost, and another exhausting, so I don't think my CPU cooler does a whole hell of a lot of the cooling).
a b à CPUs
a b K Overclocking
January 4, 2006 7:15:13 PM

Of course you're right about configurations changing results, but I've always seen a measurable difference no matter how slight.
January 4, 2006 11:20:11 PM

I am sure you are right, like I said, I don't think my CPU fan actually does very much.
January 5, 2006 7:17:11 PM

This is very interesting. I always assumed the fan was pulling air away from the heat sink, toward the exhaust fan toward the top and back of the computer case... and new cooler air would seep in through the sides of the heat sink. I was always under the impression that the general goal was to keep the air flow in the computer case streamlined, like in those smoke chambers used to test airplane wings. Thus the heat from the CPU would be caried out of the case in a smooth efficient current of air.

Blowing the fan in toward the CPU seems like pointing a fan toward a wall. It will bounce the warmed air in all directions causing turbulence in the system, not necessarily toward the top/back of the case.

I'm not saying this is wrong (or right), I'm saying it is counter-intuitive... at least from my mindset.
a b à CPUs
a b K Overclocking
January 5, 2006 8:26:32 PM

Actually, turbulance near the base is a GOOD thing, it stirs the air at the base and causes it to be expelled when it mixes with another part of the stream.

Unfortunately that's not exactly how aerodynamics works. Actually there's a slow-stirring bubble at the center of the base, that the surrounding air rides over. But there's still some mixing effect that way.

And then you compare that to the air being pulled through the sides of the top edge ot the cooler, and pushing looks good again.
December 10, 2007 9:18:13 PM


Coming to this post a little late but have been looking into this myself and want to chuck in my tuppence-worth for anyone who comes after. My first post here too! I finally decided to register as I need to ask for assistance with some other stuff but that's another story.

I have an old ATX case. the only fans are the PSU, GFX Card and CPU fans. My processor is an Athlon Thunderbird (1.1 GHz) with a basic aluminium (?) heatsink. The heatsink used to have a generic crappy fan, which blew outward, until I replaced it a while back with a quiet Acoustifan job to reduce noise levels. Without thinking I put it on the same way, i.e. blowing away from the CPU.

I'm a little more versed in PCs these days and wanted to try a bit of OC'ing, so I upped the FSB in stages and then ran CPU Stability test until it crashed. The most I found I could get was 109MHz without errors - pretty low OC really! Anyway I ran MBM5 whilst testing the chip using the CPU Warming test and noticed it was up at 58C - pretty hot but seemed stable enough. Then I had a bright idea and turned the PCU fan around. I ran the test again and MBM5 showed 54C - a 4C difference!

I belive the fact that I have not been able to raise the FSB speed any further is due to hardware limitations rather than the CPU temp (mobo is the main suspect - has bad caps, chipset seems to have IDE trouble too) but this experiment certainly shows that, for low end computers at least, a simple change like this can have a big effect. At the very least this should extend the life of the chip a little so worthwhile doing!
December 16, 2007 1:45:18 AM you realize this thread was started almost 2 years ago?
August 20, 2009 12:51:52 PM

I have a computer that sucks air in,and no one has mentioned the amount of dust this creates in the case opening and inside the case,needs to be cleaned out every 3 months or could say i need to keep my room cleaner tho lol

Regards Rob
February 11, 2010 5:29:06 PM

Intel put the sticker with the fan sucking air from the processor, and so that's how I have mine setup.
March 16, 2010 7:58:47 AM

RichPLS said:
Aree, it should blow down to the processor letting sucking the case air down and over CPU circulating cooling chipset and mem also.
My LianLi PC60plus has an intake at rear, with a duct pulling in cool outside air and blowing it towards top of CPU fan, so it can then pull cool air down to the CPU.
So down it is.

The Processor Fan be it a single, dual or quad core should always "pull" the air away from the heat sinks. The idea of blowing air back onto the heat sinks is not logical. The heat only gets dispersed over the mobo and other components----in need to drawn away from the mobo.

The case fan should always be an Exhaust fan, pulling the hot air out of the case. If you have two exahuast fans, then the lower one should push air into the case and upper one pull it out.

I have a mini-tower of which 1/3 of the case cover is a vent. I put in a high-speed manual fan with low, medium and high fan speeds. In my scenario the dual processor fan pulls the heat away from the heatsink and the case fan (on constant medium speed) pulls the hot air out of the case which pulls cool air into the case from the large mesh screen near the bottom of the removable side panel. A manually controlled case fan is so much superior over a fan controlled by sensors, and you can get them for about 10 to 20 dollars. In my case, my 9800 GT 1 GB video card, 500 Watt Power Suppy and dual core AMD 64 x2 5200+ processors are all staying cooler due to the air flow and mostly due ot the medium setting on my manually controlled case cooling fan. My processors drop 8 degrees celsius and my GPU 10 degrees celsius with a manually controlled 3 speed case fan.
March 18, 2010 11:47:48 PM

Get some programs that watch the temperatures on various items in your pc and do a bechmark with it blowing in ans sucking out. My processor already has a fan sucking it. However my drives get hot so I got the drive monitor to see which direction is the most effective.
The reason I say this is everyone has diff ideas and you might as well see what works properly for you.
a c 133 à CPUs
a b K Overclocking
March 19, 2010 12:46:56 AM

Air should be blown down onto the heat sink this process also cools everything else around it including northbridge ram and the most important the VRMs. Pulling it threw could result in the motherboard overheating. Now maybe the CPU might be better cooled with it pulling up but that fan is not just for the CPU like i said its for the motherboard too.

Now since this post is so old tower heatsinks weren't popular then with a tower heatsink it still works best with the fan blowing threw the fins and pushing it to the exhaust fan. But what a lot of people don't realize is that those tower fans do nothing for the motherboard so good case cooling is essential and all high end motherboards come with big heat sinks on the VRMs and Northbridge to take more advantage of the air flowing around the case.
a b à CPUs
a b K Overclocking
March 20, 2010 4:04:00 AM

This is interesting... a 4 year old thread resurrected but still is useful albeit with the changes in technology.

I myself set the fans to push the air thru the heatsink. The push is more directional as it makes sure the air is passing thru all the fins and going straight thru. If the fan is set to pull, then a good change the pulled air will come from the sides and not thru the heatsink as it will choose the path of least resistance... By passing thru the sides, it will not effectively pull away all the heat in the heatsink.
April 5, 2010 6:25:08 AM

Well I think Cooler Master has put the push air theory to bed. The 212 neither sucks or blows. All pun intended. It does a sort of side swipe over the fins towards the back of the case. But then, they have a whole different theory of cooling as they direct contact the cooling pipes to the cpu by cutting them through the sink.
May 22, 2010 5:05:50 PM

What is missing from this thread is empirical evidence. No one says I tested my CPU temp with the fan blowing this or that direction.

Yes, this thread is several years old, but it's still a relevant topic until a processor is designed which does not need external cooling.

When I first came to this thread I suspected the fan should be blowing away from the processor to draw the heat up the sink. After reading I can see how this would limit the air inflow to just around the edges of the sink and not in the center. Blowing air toward the center will create more airflow over the entire sink, which is the ultimate goal.

One thing aside that I can tell you from personal experience is that I work on a lot of customer's PCs and they get very dirty inside. The fan is going to draw dust into the sink, it's inevitable. I've seen it time and time again, the dust collects at the point the air first touches the sink. The question is, do you want the dust collecting near the processor because the fan is blowing away from it, or do you want the dust further away from the processor because the fan is blowing toward it. Personally, I would rather have the dust collect as far away from the processor as possible and allow the dust free fins to draw heat away from the processor. Yes, I know we should all clean our computers regularly and get the dust out, but for the average joe who never cracks the case open and has years of dust collecting inside the clear advantage is to have the fan blowing toward the processor.
June 14, 2010 6:52:52 AM

OK here's a curve ball, what about if I use this CPU coolers

(Prolimatech Megahalems Rev B CPU Cooler)

...and put two fans on it (which it allows), the one nearest the back pulling air and the on on the other side pushing air through...

Best of both worlds?
June 19, 2010 4:57:11 AM

lol. my artic circle x64 cooler blows air into the fins then air goes out exhouse fan on the back. top fan blows air also. Front has fan in and now I will install side fan blowing air in and also i have Video card blowing air down onto the PSU that sits on bottom of case installed upside down blowing its air into graphic card. So now I am ready to install side fan that will blow air IN and wh IN. because when you want to cool down you put fan to blow into your face not air away from your face. The only reason you put fan away from your face is when you smoke inside the room and want smoke out, so that fan should blow lots of air right into my mobo. vga and it will be great.
LOL if pulling air out is better why don't they have air conditioners in the car that blow air out of the car instead on your face. I mean create some suction in the car ROFL. :bounce:  :lol: 
July 8, 2010 11:17:28 PM


My friend has an HP Pavilion Elite m9250f (has Q6700). I was doing some maintenance (wouldn't boot, video card fried, replaced it), and decided to check the temps. 70C idle, 86C running Prime95. Problem. Took off the fan, and sitting on top of the heat sink was so much dust you could hardly see the heat sink. Took off the heat sink, cleaned, reseated with AS5, now 40C/70C (what I was expecting).

The heatsink fins did not look aerodynamically designed for inflow - it had hard square edges (which seems like it would encourage dust buildup). Which lead me to think about this question and wind up here.

I think a HSF could intentionally be designed for outflow, not inflow. And I'm wondering if that's what I was dealing with. Directly above the HSF, in the side of the case, it's perforated. Is this to get hot air out of the system, or to get cool air into the system and over the processor (and blow warm air over everything else)?

The dust buildup, non-aerodynamic nature of the top of the heatsink, and case perforations lead me to suspect this may have been an outflow design.

If anyone can definitively answer this, I'd appreciate it.
a b à CPUs
a b K Overclocking
July 9, 2010 8:37:11 PM

Think of it like this. If you was was all hot from doing work outside and you came in to get out of the heat and wanted some air. Would you put the fan in front of you blowing air onto you or would you turn the fan around and have it suck air around you? Makes common since that you would want the fan blowing ON you. Common guys use your heads. :o  :bounce:  :fou: 
July 9, 2010 9:07:00 PM

I think I'll think of it like this.

I suspect HP took a stock heat sink, then lopped off the top of it because it was too tall, because the case was on the thin side. That left the sharp edges which gather dust so easily. So it's probably an inflow design with a kludge. But I'm just guessing. Hi HP :p 

Again, if someone can definitively answer this, I'd appreciate it.

P.S. I could design an outflow cooling system, if I wanted to. And it would make sense in some ways (ie, getting heat out of the case as quickly as possible). So, those who are crapping on the question, and insisting that there's only one answer, aren't really helpful.
September 2, 2010 1:31:11 PM

@snowonweb & that other anonymous guy who isn't rtownsend:

The reason A/C units blow air towards us is because we FEEL the cool air on our skin and that makes us more comfortable. It doesn't actually do all that much to relieve our body of heat.

@rtownsend: Hope someone can

Hope someone can help you with your problem. =o

Beaker_GJ had a good point regarding where dust collects when fans blow or suck, but in the end, I'm going to have to go with sucking air, because it performs roughly along the same lines as exhaust fans for a PC as a whole: move hot air away, and fresh, cooler air will come in to replace it. If you have decent airflow in your case, the hot air will be whisked out the exhaust fans.

Of course, this is all moot to me, because I prefer heatsinks on CPUs. Makes more sense to me, especially with the aforementioned decent airflow and exhaust fans.
December 14, 2010 3:21:34 AM

Well, if you would be an engineer you would probably check a cooling fan spec and find that it does not like overheat! Just imaging a fan always sucking hot air from a heat-sink and heating itself. Fan's operating temperature raising above the spec, it works in stressed condition. What happens to its lubricant?.. So, you have to replace a cooling fan twice a year wondering why does not it work its 20-30k hours according to the spec...
IMHO, the only reliable way to install the fan with the air flowing towards a heat-sink.
December 29, 2010 1:58:08 AM

For CPU Heatsinks with the older style fans, the air is supposed to be blowing down onto the CPU. That is why on PCs having a side intake air duct, the shape of the duct is small to large, with the large end directly over the CPU. This shape (small to large diameter) is known as a Venturi effect. It creates a cooling effect as the air moves from the smaller end to the larger opening. Besides, go to Intel's sight (or AMD's) and read the installation guide. Come on folks!
a b à CPUs
a b K Overclocking
December 29, 2010 11:54:07 AM

This topic has been closed by Mousemonkey