2 fans per CPU

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hi there.  I'm building a box based on P4DC6+ board with two passive
copper coolers for both CPUs. The passive cooler isn't enough to
sufficiently cool the CPU's so I've decided to put some quiet 60mm fans
on the passive coolers.  since the fans I'm buying (20db, 12cfm) was
made to be quiet rather than move a lot of air, I was thinking about
putting two of these things per CPU, blowing the same direction,
towards the exhaust.  My question is - would this type of pairing
improve the cfm or somehow hurt the cooling capability in the overall
picture??  any thoughts will be welcome.  Thanks.

Re: 2 fans per CPU

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Bad move... You want LARGE SLOW fans.

For a 60mm fan to move enough air it will have to run pretty fast.

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Forget small fans.  If you want quiet, get an Arctic Cooling TC (thermally
controlled) heatsink with 96mm fans. On my Opteron system the CPU fan only
runs about half the time, and I don't hear it even when it is running.

Re: 2 fans per CPU

the only reason I'm sticking with the 60mm fan is because I would have
to buy some more parts to affix 80mm fan to a HS that has the dimension
of 60x60x60..  It would be nice though and I appreciate the feedback..
and the space is limited for one of the CPU bank to fit an 80mm fan
right on top of the CPU..  basically, there really isn't much clearance
between the top of the HS and the HD/HD cage..  I need to leave at
least an inch of clearance for the cooler air to make it into the fan

Simon wrote:
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Re: 2 fans per CPU

On 18 Jul 2006 12:01:34 -0700, jaykwon72@gmail.com wrote:

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I suppose it might be a silly question, but why are you
planning to use heatsinks already known to be inadequate?
Wouldn't that be a pretty clear disqualifier?  It's not as
though nobody makes P4 heatsinks, they come in so many
sizes, colors and flavors that you can try a different one
every week.

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What they are is small.
20db is their free air rating, but they'll have to have a
fair RPM to do that and it will produce turbulence in use.

In other words, using a larger fan rated for same 20db, the
result will be a quieter fan once it's actually installed.
Unfortunately there's no way to rate a fan's noise once
implemented unless it's already in a finished product
design... and in that case, there are some that want to
trick buyers by citing the fan's free-air rating still even
though the product will never have the fan running in free

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If you had two stacked on top blowing INTO a dense heatsink,
that would help a marginal amount.  Blowing in an more open
area as I suspect by your description, the benefit will be
very low if at all.

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It'll probably be about the same but noisier, even noisier
than having the two fans in completely different areas of
the system.

Is this some kind of odd case?  I have to wonder why you're
trying to reinvent the wheel here, since heatsinks that are
finished products and designed specifically to do what you
want to, are available at almost every place that sells the

To know if what you propose would work, we'd have to have a
better idea of exactly how it'll be set up, not in words but
pictures of it implemented.  Not necessarily two fans but at
last the one fan and how the airflow through the 'sink fins
will be maximized.  P4 just runs too hot for passive blow-by
from a low speed 60mm fan.  Medium speed 80mm fan and very
large heatsink would be closer to useful.

If your exhaust fan is large enough, you might be as well
off to construct a duct that causes all exhaust air to pass
through the heatsink fins.  OEMs such as Dell manage to do
this successfully, but you have to have a moderate speed ~
92mm fan in back and the duct has to be designed well.

Re: 2 fans per CPU

kony wrote:

re cpu overheating

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yes, a simple and silent method. Card plus some sort of tape that will
last well, not sellotape. Avoid long narrow ducting as it reduces


Re: 2 fans per CPU

thanks for the response..  let me clear some things up...

kony wrote:
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I say the HS is inadequate because it's a passive copper HS meant to be
duct cooled rather than a fan mounted on it directly..  The time/effort
of making even a simple duct, even out of cardboards, is something I
didn't want to get into..  And oh yeah, I'm on a limited budget so I
can't exactly go out and buy and try different heatsinks..  but I've
been eyeing one of those zalman coolers..

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the HS has 60x60x60 dimension and the top and the two opposite sides
are opened. I was thinking about putting two fans on two sides that are
open and blocking the top open area by soldering a piece of copper
plate or something directly onto the HS..  these two weak fans will
blow in the same direction, pulling in air from the front through the
HS - out the other fan and onto the RAM banks..

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I'm putting this into a Silverstone TJ-05..  it's a fairly large case
and it's actually the second time I'm using this box ..

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what it comes down to is that I'm trying to use the parts I already
have as a fun project to get my mind off of things..  I would really
prefer to make a duct out of acrylic material but I just don't have the
finesse and the tools to get it done..  And I've been reading about
sharp turns in air ducts actually hurt the cooling performance..
smooth, rounded out air duct would take me a while to fashion so that's
why I'm pointing to the setup where fans are used in place of air

I did get my fans the other day and experimented a bit..

I covered the top open end of the HS with a piece of paper and
basically put the two weak fans on the side open ends of the HS, again
blowing in the same direction - front to back..

And I tried another variation where a single fan is just sitting on top
of the HS blowing directly into it and exhaust out the side open ends..

the result was that in either situations, idle temp was at 41c and full
load temp was at 50c - using CPU Burn-in app..

This test was run naked, outside of a case and I suspect that the temp
readings would be higher once I stuff everything into a case..

I think my only saving grace would be the 120mm fan on the power supply
(Nexus nx-5000) sucking the heat out of the case..  but the PSU isn't
here yet and neither is the case.

I'll post some more results when I get the parts together and into a

Re: 2 fans per CPU

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Lets say each of your fans can move 10cfm of air. So now you've got fan #1,
pushing 10cfm...you add fan #2. Together they are now moving... (come on
now, guess......) 10cfm. Yup... Fan #2 is still only capable of moving
10cfm... having fan #1 won't help it much.

Another example... You've got two cars. Both can go 100km/hour. Car #1 is
going at 100km/h. Put car #2 behind it.... and they both only go 100km/h.

Re: 2 fans per CPU

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Actually. The Zalmans I have are the loudest coolers I have in my PC's. They
definately aren't loud, but they aren't silent either.

I didn't see what type of CPU you are using, but something like this cools
well and is VERY quiet:


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I was never a fan of the Silverstone cases. Quite expensive. Their media PC
cases also had atrocious layouts as well. Looking at the case you want I can
see a bunch of design flaws. This is definately overengineered and

Look at the rear fan port. I'd say that it's 75% blocked up simply due to
how it's punched out. Cut vent wide open and you'll see a BIG improvement.
Same problem in front... I don't see a lot of venting area for the 120mm fan
in front to do it's job.

The side vents are two low. A fan mounted here will have much of the airflow
blocked by PCI cards. One low and one higher vent would work better.

My suggestion? Turn the back 120mm fan around so it blows inward, across
your heatsinks. Let the PSU fan pull the warm air out. You could also
consider turing the front 120mm fan around to help in venting as well.

Personally, I'm running in this:


..and if you really like the LCD on your Silverstone, you could add this to
a better designed case


Re: 2 fans per CPU

" If you had two stacked on top blowing INTO a dense heatsink,  that
would help a marginal amount."

good of you to mention this..  I've been reading about fan stacking and
apparently, one needs to rotate the blades in the opposite direction,
but the same direction..  I want to do this too if at all possible.
However, if I flip the polarity on one of the fans, does that
effectively flip the wind direction as well??

Re: 2 fans per CPU

I didn't make sense just now.  what I meant was,

two fans, stacked on top of each other..

one fan rotating clock wise and another fan rotating counter clockwise
- blowing in the same direction...

sorry about that..

blah00000 wrote:
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Re: 2 fans per CPU

On 19 Jul 2006 12:34:12 -0700, "blah00000"

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Unless you're stuck on a remote island somewhere with no way
to get fans, the obvious choice is a larger fan, thicker
fan, or larger heatsink.

Yes you can stack them and it will maintain the air pressure
better into a 'sink, but it's not common to find two decent
fans that rotate opposite directions and you can't flip it
over to achive that, nor reverse the power polarity.

It doesn't do as well as a thicker fan, it's not really all
that useful in most situations.

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