Sign in with
Sign up | Sign in
Your question
Closed

Which way do fans blow???

Last response: in CPUs
Share
April 29, 2007 4:37:07 PM

Some quick questions:

1. The heatsink fan over the CPU: does this blow air into the CPU (into the mobo) or up away from the CPU?

2. Side panel fan (right above the CPU when the side panel is placed back on the case): Should this blow into the case (and into the CPU) or out of the case away from the CPU?


EDIT: While I'm at it, some more questions hehe:


3. To which side do the fans blow? Blow air through the side with the sticks?

For example: http://en.wikipedia.org/wiki/Image:IMG_1549.JPG

Would this blow up or down?

4. I have different strength fans (one came w/ case, two I bought). Do I want the stronger one in the front intake, or stronger in the back for exhaust? (Or side panel fan?)

(Came w/ case: Raidmax generic 80mm; Two I bought: Antec TriCool (Adjustable 3 speed) http://www.antec.com/us/productDetails.php?ProdID=75080 )

More about : fans blow

April 29, 2007 4:48:34 PM

Quote:
Some quick questions:

1. The heatsink fan over the CPU: does this blow air into the CPU (into the mobo) or up away from the CPU?


No, it blows air away from the CPU. It takes all the hot air from the heatsink and blows it in the case.

Quote:
2. Side panel fan (right above the CPU when the side panel is placed back on the case): Should this blow into the case (and into the CPU) or out of the case away from the CPU?

It blows air out of the case.

Quote:
EDIT: While I'm at it, some more questions hehe:


3. To which side do the fans blow? Blow air through the side with the sticks?

For example: http://en.wikipedia.org/wiki/Image:IMG_1549.JPG

Would this blow up or down?

4. I have different strength fans (one came w/ case, two I bought). Do I want the stronger one in the front intake, or stronger in the back for exhaust? (Or side panel fan?)

You want the stronger one blowing air OUT of the case in the back. You always want one 80mm fan infront blowing in air, and one 120mm fan blowing air out. You wouldn't want more air blowing in than out of the case.
April 29, 2007 5:16:28 PM

Many traditional CPU coolers blow air down onto the heatsink/CPU.
Related resources
April 29, 2007 5:52:30 PM

But then you'd get dust all over your mobo and heatsink. Plus it won't blow as much air because the heatsink is in the way.
April 29, 2007 6:15:16 PM

With the exception of some OEM cases that are designed to have one fan cooling the whole system, and thus suck air up and blow it out of the case, nearly all CPU fans blow down on the CPU. Take off the fan after it's been running for a few months, you'll find dust all in the fins and on the heatsink.
April 29, 2007 6:15:32 PM

But wouldn't you want to get rid of the hot air as soon as possible, not blow it all over the mobo? Then you could have cool air from an intake cool the mobo then the heatsink, and then blow out of the case? Thats what I always thought, but I never did any tests or anything.
April 29, 2007 6:16:25 PM

Quote:

The actual fan that screws to the heatsink always have a arrow on the side showing air flow direction. This goes for case fans too.

true you hit the nail in the head :arrow:
April 29, 2007 6:19:56 PM

Quote:
But wouldn't you want to get rid of the hot air as soon as possible, not blow it all over the mobo? Then you could have cool air from an intake cool the mobo then the heatsink, and then blow out of the case? Thats what I always thought, but I never did any tests or anything.


That's what case fans are for, to suck out the hot air before it builds up. Sucking air up from around the motherboard and through the CPU heatsink would have warmer air (from the warmth of motherboard components) trying to cool the CPU, and sucking it up through gets significantly less airflow on the heatsink bottom (where the fins connect).

It just doesn't work as well. Most high-end HSF units, as mentioned, blow the air towards the back of the case these days.
April 29, 2007 6:20:05 PM

In the middle of summer, which do you prefer, the fan to be pointed right at you, or pointing away from you? That answers the CPU question.

For case fans, generally one big fan pulling in air from the front, and a side port and top port draw the air in, and a bunch of fans push it out of the back of the case.

Addendum/edit: ajfink makes a good point in that hot air does rise, and a top fan pulling air out of the case would be a very good idea. Front and side ports still seem to be where the most air is drawn in from.

Myself, I have the side of my case open and a miniature box fan pointed right at the CPU and passively cooled graphics card. Doesn't help the CPU at all, but the motherboard and GPU definately appreciate it.
April 29, 2007 6:20:50 PM

Quote:
In the middle of summer, which do you prefer, the fan to be pointed right at you, or pointing away from you? That answers the CPU question.

For case fans, generally one big fan pulling in air from the front, and a side port and top port draw the air in, and a bunch of fans push it out of the back of the case.


I prefer my top fan sucking out the hot air that rises.
April 29, 2007 6:24:49 PM

heatsink fan should blow into the heatsink


case fans..... just plug them in when the case is open, turn on your computer and use your hand to feel which way they blow since some fans are different than others.


should have a faster rpm front intake than rear exhaust
April 29, 2007 6:26:41 PM

Quote:
4. I have different strength fans (one came w/ case, two I bought). Do I want the stronger one in the front intake, or stronger in the back for exhaust? (Or side panel fan?)

You want the stronger one blowing air OUT of the case in the back. You always want one 80mm fan infront blowing in air, and one 120mm fan blowing air out. You wouldn't want more air blowing in than out of the case.

Ahhh! Makes sense!

Quote:
In the middle of summer, which do you prefer, the fan to be pointed right at you, or pointing away from you? That answers the CPU question.


Aha! Good analogy!

Thanks guys
April 29, 2007 6:32:20 PM

Quote:
But wouldn't you want to get rid of the hot air as soon as possible, not blow it all over the mobo? Then you could have cool air from an intake cool the mobo then the heatsink, and then blow out of the case? Thats what I always thought, but I never did any tests or anything.


That's what case fans are for, to suck out the hot air before it builds up. Sucking air up from around the motherboard and through the CPU heatsink would have warmer air (from the warmth of motherboard components) trying to cool the CPU, and sucking it up through gets significantly less airflow on the heatsink bottom (where the fins connect).

It just doesn't work as well. Most high-end HSF units, as mentioned, blow the air towards the back of the case these days.

But you if created the same conditions as a case and you sat in a narrow tunnel with a high rpm fan in front of you, wouldn't the air being pulled into the fan cool you first? Also, wouldn't the dust build up in the heatsink cause the fan not to blow as much air? I say this because my brother gave me this computer once with the fan blowing onto the heatsink. The fan blew like no air and there was dust all over the mobo. So after I cleaned it and switched the fan the other way, it blew air like crazy.

Which way is the stock intel or amd hsf facing?
April 29, 2007 6:40:13 PM

Quote:
99% blow air down into the heatsink. Some like the AC Freezer7 pro, blow it through fins and accross heatpipes and toward the back of the case where the case fans blow it out.
Im not sure what kind of hsf the first poster has but Ive never seen one that sucks air up.. 8O
The actual fan that screws to the heatsink always have a arrow on the side showing air flow direction. This goes for case fans too.


Mine blows air towards the heatsink, he asked which way it should blow. Hot air will form in the fins of the heatsink, so you'd need the cpu fan to take the hot air and blow it towards the case so it can be blown out of the case. The side panel fans are helpful because instead of the hot air going into the case, they go directly outside the case thus resulting in a cooler environment. You never want too much air blowing inside the case, thus making the side vents useless.
April 29, 2007 6:42:46 PM

Quote:
In the middle of summer, which do you prefer, the fan to be pointed right at you, or pointing away from you? That answers the CPU question.



probably the best one 8) :lol: 
April 29, 2007 6:43:48 PM

Quote:
No, it blows air away from the CPU. It takes all the hot air from the heatsink and blows it in the case.
8O :?:
April 29, 2007 6:52:27 PM

Found interesting link on google: http://www.opentechsupport.net/forums/archive/topic/32585-1.html

The one guy says this:
"heatsinks are sometimes designed to have the airflow going a certain way. assuming you followed the instructions for that, you wont get an improvement by changing the fan around. if there werent any instructions, its usually safe to assume that the cooling wont change significantly with the airflow direction."

So maybe it also depends on type of heatsink? I always just figured that dust buildup and turbulance from the fins on the heatsink would kill airflow.

Also, I find it really annoying to have a fan blowing on me.
April 29, 2007 7:03:37 PM

Quote:
So maybe it also depends on type of heatsink?


Exactly.
a b à CPUs
April 29, 2007 7:04:59 PM

I have only had one CPU fan suck air away from the processor, and that was in a PIII 866MHz Dell.

Here is my suggestion, it is what I use for the system in my sig.

1.) A Large front fan, 120MM size, blowing in.
2.) GPU coolers that blow out the back of the case.
3.) A side fan that sends cool air directly onto the processor fan, in.
4.) A rear 80MM fan, blowing out.
5.) Most PSU have a rear fan that blows out.
6.) I have a mushroom shaped CPU cooler, so the side air duct works great.

You don't need a big rear fan because you have the GPU(s) and PS also blowing out.
April 29, 2007 7:08:54 PM

Quote:
A Large front fan, 120MM size, blowing in.


Quote:
A rear 80MM fan, blowing out.


Probably better to have these reversed.
a b à CPUs
April 29, 2007 7:15:12 PM

I think that depends on your setup. In my case, I wanted the 120 in the front and 80 in the back becaue I already had so many blowing out.
I had :
Out : 80MM rear, 120MM PSU rear, and 2x 100MM GPU rear.
In : 120MM front and 80MM side.

So in my case, I wanted a big front in fan. If you dont have as many
rear fans, you then may want to get a smaller front fan.
April 29, 2007 7:24:37 PM

I have the opposite with the 80mm in front and 120mm in rear.
I have tried a 120mm in front but seen no difference.
Didnt even see a difference going to just one rear 120mm fan.

If i turn up the fan speed then i see a big difference.
And hear it too :lol: 
a c 108 à CPUs
April 29, 2007 8:18:49 PM

I drop by the the local home improvement warehouse and buy a replacement HVAC filter. The good ones contain *MERV* ratings (Minimum Efficiency Reporting Value) which is the standard comparison of the efficiency of an air filter.

The MERV scale ranges from 1 (least efficient) to 16 (most efficient), and measures a filter's ability to remove particles from 3 to 10 microns in size.

The media maintains high air flow capacity. I prefer something around MERV 8. Using a utility knife you can carve out a filter for your intake fans.

see: http://www.home.earthlink.net/~highland1/images/fan-fil...

I use a vantec double ball bearing 92mm fan for my side intake. I think it's around 20db's.
http://www.home.earthlink.net/~highland1/images/fan-fil...
http://www.home.earthlink.net/~highland1/images/fan-fil...
I also filter my power supply (which I think blows air into the case). I intake from the front (also filtered) with an 80mm FAN) blowing across my HD's and finish if off with a 120mm exhaust in the back.

I try to balance intake/exhaust flows but if there is any question I'll pull a bit more air into the case.

I seldom have any problems with dust or overheating. It also impresses your clients - especially after you show them a fried cpu/mobo that's covered in dust . . .
April 29, 2007 8:32:43 PM

Quote:
by all means try the cpu fan sucking air up, If you can keep the pc up and running and disable any heat protection youll likely damage the cpu. Air must be forced down onto the metal surface to dissapate the heat by cooling the surface of the metal. Having it in reverse would dilute the force of air against the metal and cause overheating.

Without the air forced onto the base the fins would have to disperse most of the heat as air is sucked up, making the base warmer.


Nah I've switched them before for shits and giggles, it still works, just not as well. As long as there's a decent amount of air being moved over the heatsink most processors won't overheat.
April 29, 2007 8:46:06 PM

Cpu fans blow cooler air onto the heatsink,thereby cooling the fins and blowing the air across the board.Now sometimes you can change it around,(the fan),and it might cool better.But it is best to leave it as is for the most part.Cpu manufacturers have put a lot of time into cooling options,and they usually do fine.Although if you want better cooling,go with an aftermarket cooler as these will usually perform better than stock HSF.Goodluck.

Dahak

AMD X2-4400+@2.6 TOLEDO
EVGA NF4 SLI MB
2X EVGA 7950GT KO IN SLI
4X 512MB CRUCIAL BALLISTIX DDR500
WD300GIG HD/SAMSUNG 250GIG HD
ACER 22IN WIDESCREEN LCD 1600X1200
THERMALTAKE TOUGHPOWER 850WATT PSU
COOLERMASTER MINI R120
3DMARK05 13,471
a c 108 à CPUs
April 29, 2007 8:55:21 PM

Yeah . . .I kinda worry about the pci bus . . I convince myself that the front fan blows a little air in that direction. I try to keep the case as tight as I can to keep the bad stuff out . .

I'd be a little more concerned with dead air if I had the same number of intakes/exhausts thereby creating the type of *equalization* I think you're talking about. By pulling air in three places and exhausting at one I figure I'm at least moving air around . . . even if it's like the hot air floating around here sometimes . .. :p 

Be interesting for THG to do *case air flow* dynamics investigation . . .
April 29, 2007 9:06:10 PM

Quote:
by all means try the cpu fan sucking air up, If you can keep the pc up and running and disable any heat protection youll likely damage the cpu. Air must be forced down onto the metal surface to dissapate the heat by cooling the surface of the metal. Having it in reverse would dilute the force of air against the metal and cause overheating.

Without the air forced onto the base the fins would have to disperse most of the heat as air is sucked up, making the base warmer.


Nah I've switched them before for shits and giggles, it still works, just not as well. As long as there's a decent amount of air being moved over the heatsink most processors won't overheat.

did you load your cpu with orthos or prime to see how well it didnt work?

Nope, but the temps (while folding) only changed a few degrees.

On a related note, I have to keep my P4 folding rig's side open to keep the temps below 50C. It's a Northwood, can't imagine what a Prescott would be like. It's a really old case that came with a 466 Celeron system, so cooling wasn't a big deal when it was put together. One 60mm intake and one 80mm exhaust.
April 29, 2007 9:06:31 PM

When it comes to heatsinks, it a matter of simple physics for having the fans blowing air onto them. The air blows onto the heatsink, across the fins absorbing the heat, and continues to move away from the heatsink. Air is the medium that absorbs heat and carries it away. If the fan was blowing away from a heatsink, especially stock ones with vertical fins, it would create a low pressure area over the heatsink. This results in less air contacting the heatsink to remove heat. Yes, some air would be "sucked" through the fins and out the fan. But the reisitance of the air having to be sucked through the fins and from air being sucked into the fan that has not passed through the heatsink first would result in less air coming in contact with the fins. This would result in far less cooling.
April 29, 2007 9:17:40 PM

I have (a different) P4 folding rig, 2.6C in a Gateway rig. It's one of the ones that is designed for single-fan cooling. It's always opened up because the proprietary PSU went bad and it's running off of a standard, really cheap ATX PSU at the moment (like $15 from Newegg). Anyway, I just took off the fan and flipped it on end (so it was blowing down on the CPU) and the temp went from 53C to 49C. The heatsink is tiny and sucks, but the mounting bracket (and the screws that hold the bracket on) are, of course, also proprietary, otherwise I'd have a better HSF on it.

So, even even systems designed to have air sucked over the HSF don't always work the best that way. The heatsink is very small, thus allowing for the most amount of air contacting the base of the heatsink, but even that doesn't remove the deficit.
January 21, 2012 9:27:04 PM

ajfink said:
With the exception of some OEM cases that are designed to have one fan cooling the whole system, and thus suck air up and blow it out of the case, nearly all CPU fans blow down on the CPU. Take off the fan after it's been running for a few months, you'll find dust all in the fins and on the heatsink.

Please don't pretend to offer misinformation as qualified advice. A CPU fan is an exhaust fan - in other words it is designed to evacuate heat. The air inside a case is warm to hot, so the idea of blowing hot air onto a CPU can be equated to a convection oven which would act to melt your CPU. For the case exhaust fan to effectively evacuate hot air from the case, adequate ventilation (i.e. air flow drawn across the case) is ideal and is accomplished by installing a blower fan opposite the exhaust fan to draw air into the case.
a c 190 à CPUs
January 22, 2012 12:37:17 AM

This topic has been closed by Hunter315
!