OT fan question: suck or blow, which is best?

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mr_buggerlugs

I'm attempting to lower my cpu temp and currently have my xp1800+
running at 1545mhz kicking out 55-60 Celsius. Case temp is 24C.

I have 4 80mm 3000rpm case fans (2 front - 2 back) and a socking great
coolermaster aluminium heatsink and fan (4200rpm) which sucks air off
the heatsink.

Is it worth my while turning the fan on the heatsink around so it
blows instead of sucking? I'm just wondering because with so much cold
air blowing through my case the heatsinks fan seems very ineffective.
 
I'm attempting to lower my cpu temp and currently have my xp1800+
running at 1545mhz kicking out 55-60 Celsius. Case temp is 24C.

I have 4 80mm 3000rpm case fans (2 front - 2 back) and a socking great
coolermaster aluminium heatsink and fan (4200rpm) which sucks air off
the heatsink.

Is it worth my while turning the fan on the heatsink around so it
blows instead of sucking? I'm just wondering because with so much cold
air blowing through my case the heatsinks fan seems very ineffective.
Click to expand...

Blowing air into the HS should work better, I've never seen a boxed
Intel or AMD HS/fan that was set up to suck air from the heatsink, if it
worked better they would set them up that way no doubt or put even
cheaper fans on them to compensate for it and save a few $. ;p

Ed
 
I would not re-engineer the heatsink/fan. You'll end up pushing hot
air back onto the CPU, rather than propelling it up and away like it's
supposed to.

It's all about smooth and properly directed airflow, not disruptive
turbulence created by too many fans. Reversing your CPU fan may have
dire consequences, and most certainly, would void any kind of
warranty. It may even kill your processor, if not immediately, than
sooner than expected. I recommend leaving it alone. If someone is
serious about reducing case and CPU temperatures to a minimum, they
will look into alternative liquid cooling systems.
 
Chiatzu said:
I would not re-engineer the heatsink/fan. You'll end up pushing hot
air back onto the CPU, rather than propelling it up and away like it's
supposed to.

It's all about smooth and properly directed airflow, not disruptive
turbulence created by too many fans. Reversing your CPU fan may have
dire consequences, and most certainly, would void any kind of
warranty. It may even kill your processor, if not immediately, than
sooner than expected. I recommend leaving it alone. If someone is
serious about reducing case and CPU temperatures to a minimum, they
will look into alternative liquid cooling systems.
Click to expand...

On my PIII/800MHz with simple cooler, the air is blown into the heatsink. So
I always thought it was the proper way. It's not??
 
On my PIII/800MHz with simple cooler, the air is blown into the heatsink. So
I always thought it was the proper way. It's not??
Click to expand...
All the CPU fans I have seen have the air blown away from the HS.
 
Andrew said:
All the CPU fans I have seen have the air blown away from the HS.
Click to expand...


Thats pretty odd since probably at least 95% of them blow onto the heatsink.

Ben
 
I'm attempting to lower my cpu temp and currently have my xp1800+
running at 1545mhz kicking out 55-60 Celsius. Case temp is 24C.

I have 4 80mm 3000rpm case fans (2 front - 2 back) and a socking great
coolermaster aluminium heatsink and fan (4200rpm) which sucks air off
the heatsink.

Is it worth my while turning the fan on the heatsink around so it
blows instead of sucking? I'm just wondering because with so much cold
air blowing through my case the heatsinks fan seems very ineffective.
Click to expand...

ooh a debate!
 
Finned heatsinks work better with the fan blowing down, but heatsinks with a
grid of vertical pins are more efficient with the fan "sucking" up.

On this page
http://www.dansdata.com/coolercomp.htm
there is a comparison of an awful lot of heatsinks. In the section about the
Alpha PAL8045, a cooler with pins, he says...

"Incidentally, the fan should correctly be installed to suck air upwards
through the heatsink, not blow air downwards onto it. In the picture of the
assembled cooler above, the fan's upside down. Mea culpa. I tested both
arrangements and the difference between sucking and blowing is 5% at most,
but you might as well have that extra 5% as not."
 
Blow air in. I like the example, do you stand behind the fan or in front of
the fan to cool off.


Joltjocky
 
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Andrew said:
All the CPU fans I have seen have the air blown away from the HS.
--
Click to expand...

Then all the heatsinks you have seen must be Alphas...because all the rest
blow into the HS...it really does not make much difference anyway.
 
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Donald Witmer said:
Blow air in. I like the example, do you stand behind the fan or in front of
the fan to cool off.


Joltjocky
Click to expand...
Then why do some of the best heatsinks around i.e. Alphas have the fan
sucking????...As long as the air is directed over the fins (Alphas use a
shroud to achieve this) it works either way
 
I am in the midst of an experiment running the fans in both directions. My
initial results are pretty similar both ways. Being into electronics I can
tell you that manufacturers don't want to suck the hot air over the fan
because it will lower the fans life expectancy because the bearings run
hotter. My setup is as follows

A7N8X-deluxe Rev 1.04 1007bios
2500 Barton
SLK-800 Heatsink
Vantec Stealth 80mm fan (2000rpm) for CPU
2 Panaflow undervolted to 5v case fans

My results
Stealth Fan Sucking 44-47c average use
Stealth Fan Blowing 44-47c average use

In the above case it makes more sense to blow because the fan will last
longer.

It does however seem logical that sucking would lower temps because you are
not forcing the hot air back down toward the CPU. This may work well if you
have an ambient air supply coming directly from the exterior of the case
feeding the base of the heatsink. Shrouding to direct the airflow like this
is next on my list.
I could care less about the fan life, I just want the thing to cool
efficiently and quietly.

David
 
I'd suggest opening up your case, turn off all case fans then run the
machine until temps stabilize then you have a baseline of what the heatsink
and fan is capable of in open air conditions. Flip over the CPU fan and
repeat the baseline so you'll know 100% if sucking or blowing is better.
This shows you which needs work - better case ventilation or a better
heatsink fan combo. If your temps are good without the case covers then
change the case fans around until you have the perfect setup. I would make a
table with OFF-IN-OUT and then start experimenting. Some people claim it's
better to run negative pressure and have most fans pushing out.

You should not need to use 4 fans. Also your temps seem very high so I
wonder if your heatsink is set up correctly.

After you can tell us, does blowing suck, or sucking blow ?

David
 
Echo said:
I am in the midst of an experiment running the fans in both directions. My
initial results are pretty similar both ways. Being into electronics I can
tell you that manufacturers don't want to suck the hot air over the fan
because it will lower the fans life expectancy because the bearings run
hotter. My setup is as follows

A7N8X-deluxe Rev 1.04 1007bios
2500 Barton
SLK-800 Heatsink
Vantec Stealth 80mm fan (2000rpm) for CPU
2 Panaflow undervolted to 5v case fans

My results
Stealth Fan Sucking 44-47c average use
Stealth Fan Blowing 44-47c average use

In the above case it makes more sense to blow because the fan will last
longer.

It does however seem logical that sucking would lower temps because you are
not forcing the hot air back down toward the CPU. This may work well if you
have an ambient air supply coming directly from the exterior of the case
feeding the base of the heatsink. Shrouding to direct the airflow like this
is next on my list.
Click to expand...

But, when you are blowing, you are blowing any excess air directly onto the
hottest part(s) of the HSF (nearest the CPU). When you are sucking, you are
drawing air in from all available areas of the heatsink, thus not providing
the greatest flow of air nearest the CPU. Of course, this depends on the
heatsink design and composition and how much CFM you are working with, and
even then I'm not sure it'd make a significant difference in a best-case
scenario....
 
MRdancer,
Yes you are correct. I think it is more logical to suck the air out but
again if you are a maker of heatsink fans or CPUs for that matter you can
get away using a cheaper fans because the heat will not be a major design
comsideration as the cooling air also cools the fan.

David
 
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