sucks or blows, which is better?


A

Al Smith

Right now I've got my case fan sucking cool air into my case from
the back and passing it over the CPU. I set it up this way because
the power supply is blowing warm out out the back of the case.

I'm wondering which is better, having a case fan suck in cool air,
or blow out hot air? The fan is reversable, but I haven't yet
tried turning it around. I did try unplugging it. Didn't make any
difference to the CPU, but the motherboard got a bit warmer. I
don't see much use in having a case fan at all, unless I can get
it to cool the CPU a degree or two.
 
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A

Al Smith

Two at the same time where each is doin one of those is the most fun.

Uhhhh, yeah... we are talking computers, right?
 
D

Dave C.

Al Smith said:
Right now I've got my case fan sucking cool air into my case from the back
and passing it over the CPU. I set it up this way because the power supply
is blowing warm out out the back of the case.

I'm wondering which is better, having a case fan suck in cool air, or blow
out hot air? The fan is reversable, but I haven't yet tried turning it
around. I did try unplugging it. Didn't make any difference to the CPU,
but the motherboard got a bit warmer. I don't see much use in having a
case fan at all, unless I can get it to cool the CPU a degree or two.

Generally, you want high mounted fans blowing out and low mounted fans
sucking in. Ideally, you want airflow in to match airflow out (and don't
forget about the PSU fans blowing OUT). Assuming the power supply has 2
fans, those are (essentially) 2 fans working together blowing OUT. That
means you want two fans sucking in. But it's better if those two fans
sucking in are mounted low (heat rises). So your two case fans sucking air
in should be mounted low in front or low on the side (some cases allow
this). But if you insist, you can have one mounted in the back blowing in.
It won't hurt anything.

OH, and your CPU has it's own cooling fan. If you want your CPU to be
cooler, you need to get a new HSF for the CPU. The case fans are for all
your other vital components. You CAN use a case fan to blow cool air toward
the CPU cooler, but that should not be a primary use for your ONLY case fan.
IMHO -Dave
 
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Guest

Al Smith said:
Right now I've got my case fan sucking cool air into my case from
the back and passing it over the CPU. I set it up this way because
the power supply is blowing warm out out the back of the case.

I'm wondering which is better, having a case fan suck in cool air,
or blow out hot air?

There's no way to know without testing the fan both ways and taking
temperatures. Be sure to test under the same conditions, with the
same software running, and wait at least an hour each time because
temperatures need that much time to stabilize (actually they usually
continue to increase for up to 3 hours). Measure external temperature
as well as internal, and use the fan direction that results in the
lowest temperature difference.

Generally the more airtight a case is, the more likely the case fan
should bring in cool air, while a leaky case will probably run cooler
when the case fan exhausts hot internal air.
 
A

Al Smith

I'm wondering which is better, having a case fan suck in cool air, or blow
Generally, you want high mounted fans blowing out and low mounted fans
sucking in. Ideally, you want airflow in to match airflow out (and don't
forget about the PSU fans blowing OUT). Assuming the power supply has 2
fans, those are (essentially) 2 fans working together blowing OUT. That
means you want two fans sucking in. But it's better if those two fans
sucking in are mounted low (heat rises). So your two case fans sucking air
in should be mounted low in front or low on the side (some cases allow
this). But if you insist, you can have one mounted in the back blowing in.
It won't hurt anything.

Well, I just turned the case fan around. It's mounted high, under
the power supply. Result, a 5 C temperature drop in my CPU
temperature under full load. It was running 63 C. Now it's running
58 C playing the same game. So I guess sucking warm air out of the
case is better than blowing cold air into it -- for my setup, at
least. It's stabilized at 58 C, meaning it isn't getting any
hotter. Flat line on the temperature graph, so that must be the
max with this configuration.

When I opened the case to turn the fan, the heat just radiated out
at me. It was hot in there! Those Athlon 64s make great space heaters.

I did get several general protection faults, but only those times
when I was exiting the game to check the CPU temperature. I don't
think this is a heat problem, I think it's a quirk with this game
and Windows XP, but I'll have to use the computer with other
games, and max out the temperature for a few days, to see if it
was only this game, or a heat problem.
 
D

David Maynard

Al said:
Right now I've got my case fan sucking cool air into my case from the
back and passing it over the CPU. I set it up this way because the power
supply is blowing warm out out the back of the case.

I'm wondering which is better, having a case fan suck in cool air, or
blow out hot air? The fan is reversable, but I haven't yet tried turning
it around. I did try unplugging it. Didn't make any difference to the
CPU, but the motherboard got a bit warmer. I don't see much use in
having a case fan at all, unless I can get it to cool the CPU a degree
or two.

The rear case fan should be exhausting out the back just as the PSU fan is.
 
D

David Maynard

Al said:
Well, I just turned the case fan around. It's mounted high, under the
power supply.

You always want that fan exhausting. Otherwise you're short circuiting case
airflow, I.E. the PSU draws it's air from that fan instead of across the
case and the front inlets, and you're recirculating warm PSU exhaust back
into the case.
 
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Gianmaria Fontana di Sacculmino

Il giorno Sat, 02 Oct 2004 22:42:48 GMT, Al Smith
I'm wondering which is better, having a case fan suck in cool air,
or blow out hot air?

I read all the replies you got and it seems that all agree with the
standard layout of the tower case: PSU on the top blowing out and low
front fan sucking in.
I do not agree on the front fan; it is rather useless especially if
the PSU has 2 fans. The airflow created by PSU is excellent and is
enough to suck air from the lower ventilation holes.
It is the same principle of the ventilated roof. If you read the paper
"AMD Athlon system cooling guidelines", they also agree that the front
fan is not essential.
 
R

Ron Reaugh

A second order effect to remember about fans is that they are electrical and
not 100% efficient. Their motors do create some heat. Any fan blowing out
carries its own heat away from the case. Any fan blowing in adds heat
inside the case.

That's why I always use outblowing fans and never inblowing fans.
 
D

David Maynard

Gianmaria said:
Il giorno Sat, 02 Oct 2004 22:42:48 GMT, Al Smith



I read all the replies you got and it seems that all agree with the
standard layout of the tower case: PSU on the top blowing out and low
front fan sucking in.
I do not agree on the front fan; it is rather useless especially if
the PSU has 2 fans. The airflow created by PSU is excellent and is
enough to suck air from the lower ventilation holes.
It is the same principle of the ventilated roof. If you read the paper
"AMD Athlon system cooling guidelines", they also agree that the front
fan is not essential.

I agree on the non essential front case fan with the exception of the swiss
cheese cases with holes stamped all over the stupid things, in which case
(pun) a front case fan can be useful, such as for directing some air over
the hard drives, because the in draft of the rear fans is going to be lost
through the chicken wire walls.
 
K

Ken

Right now I've got my case fan sucking cool air into my case from
the back and passing it over the CPU. I set it up this way because
the power supply is blowing warm out out the back of the case.

I'm wondering which is better, having a case fan suck in cool air,
or blow out hot air? The fan is reversable, but I haven't yet
tried turning it around. I did try unplugging it. Didn't make any
difference to the CPU, but the motherboard got a bit warmer.
I don't see much use in having a case fan at all, unless I can
get it to cool the CPU a degree or two.

http://w1.857.telia.com/~u85710476/docs/image/example/pcvent.png
 
T

ToolPackinMama

Gianmaria said:
Il giorno Sat, 02 Oct 2004 22:42:48 GMT, Al Smith


I read all the replies you got and it seems that all agree with the
standard layout of the tower case: PSU on the top blowing out and low
front fan sucking in.
I do not agree on the front fan; it is rather useless especially if
the PSU has 2 fans. The airflow created by PSU is excellent and is
enough to suck air from the lower ventilation holes.
It is the same principle of the ventilated roof. If you read the paper
"AMD Athlon system cooling guidelines", they also agree that the front
fan is not essential.

I just built a Athlon XP system and the only fans in it are the PS fans
and the CPU fan. The CPU temp stays under 100 f. and the sys is nice
and quiet.

It's a Biostar all-in-one mobo (onboard vid and sound) which helps it to
stay cool in there. If I started adding in a beefy video card and sound
card, etc. it probably would need another fan.
 
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Gianmaria Fontana di Sacculmino

Il giorno Sun, 03 Oct 2004 04:01:32 -0500, David Maynard
(pun) a front case fan can be useful, such as for directing some air over
the hard drives,

These modern superfast HDs really need to be cooled. Reading the HD's
user guide of 7500 and 10000 rpm drives you are told to use proper fan
toward HD. This is what I have done for the past 3 years and this is
the main reason to build a silent pc. I will build passive dissipator
for my HDs. I will post pictures when the project will be completed.
So far I have all the components on the table but the wood cabinet is
still in progress.
 
A

Al Smith

Well, I just turned the case fan around. It's mounted high, under the power supply.
You always want that fan exhausting. Otherwise you're short circuiting case airflow, I.E. the PSU draws it's air from that fan instead of across the case and the front inlets, and you're recirculating warm PSU exhaust back into the case.

What you say makes perfect sense, and I did think of it after
changing the direction of the fan's air flow. I'm surprised it
made so much of a difference, however. Five degrees C is
considerable! In my setup, a front mounted fan is not really a
good option because the ribbon cables and wires would hang down in
front of it and spoil the air flow. I mounted the rear fan high
because that's where the mounting holes were.

I wish my box were running a bit cooler. The Thermaltake fan is
fairly quiet, which is what I needed (the stock AMD fan was
driving me nuts with its buzzing), but it isn't as good at cooling
as the AMD -- simply because it runs under 3000 rpm, whereas the
AMD fan would kick up to 6000 rpm when required by CPU
temperature. Mind you, the Thermaltake is a superior heatsink and
fan, but you can't compensate with copper fins for double the fan
blade speed.

My next move, if I feel like spending the cash, will be to upgrade
my power supple to a two-fan, extra quiet PSU (I was looking at an
Ion in the local shop) that should move more air more quietly than
my present PSU. I doubt the advantage in heat reduction and noise
reduction will be very much, so I'm in no hurry to do this.

Probably what I should do is get some Arctic Silver and try
reseating my CPU heatsink -- I suspect some of the CPU heat may be
due to a poor contact with the zinc oxide paste that I applied to
the Thermaltake. Then again, reseating it may make no difference
at all.
 
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A

Al Smith

I just built a Athlon XP system and the only fans in it are the PS fans
and the CPU fan. The CPU temp stays under 100 f. and the sys is nice
and quiet.

It's a Biostar all-in-one mobo (onboard vid and sound) which helps it to
stay cool in there. If I started adding in a beefy video card and sound
card, etc. it probably would need another fan.

That's a great temperature, but is it your regular running
temperature, or your temperature under full load? My running
temperature is now (I'll just check) 42 C (107 F)for the CPU and
38 C (96 F) for the motherboard. But when I play a game, that
gradually goes up to 58 C for the CPU (with my changed fan setup)
and stays there. The motherboard doesn't change that much. Surfing
the Net or using a simple program like a word processor is not
much different from idling, I've found. Games, on the other hand,
really stress the CPU. It's all those little triangles they need
to draw.
 

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