Case Fans which way in or out

  • Thread starter Thread starter RogerRabbit
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RogerRabbit

What is the best way to set your case fans (3-4 fans) all in or
blowing out or somewhere in between
 
I put my fans on the front of the case to blow into the case and the fans on
the back to blow outwards.
 
What is the best way to set your case fans (3-4 fans) all in or
blowing out or somewhere in between
Click to expand...

Generally one more fan blowing in than out, taking into consideration the
PSU fan.

This creates a positive pressure in the case.

Lane
 
Lane said:
Generally one more fan blowing in than out, taking into consideration the
PSU fan.

This creates a positive pressure in the case.
Click to expand...

This depends totally on your environment. In a dusty environment, yours
is a good solution - no air and dust entering case through drive openings.

In a low dust or no dust environment, you *want* cool air flowing over
your drive devices, so exhaust fans should out number input fans, that
is, more fans blowing out than blowing in.
 
What is the best way to set your case fans (3-4 fans) all in or
blowing out or somewhere in between
Click to expand...

AMD recommends having your fan (or fans) blowing out at the back of the
case. That pulls the air through the case and over the CPU. I've noticed
that cases come set up that way these days, whereas a few years ago they
always had a fan in the front blowing in. That's the way I do it.
 
ric said:
This depends totally on your environment. In a dusty environment, yours
is a good solution - no air and dust entering case through drive openings.

In a low dust or no dust environment, you *want* cool air flowing over
your drive devices, so exhaust fans should out number input fans, that
is, more fans blowing out than blowing in.
Click to expand...

Why does more exhaust fans mean more air ?

Lane
 
Why does more exhaust fans mean more air ?
Click to expand...

Who said it does?

All I said is that having more exhaust fans than input fans (or more
accurately more exhaust fan CFM than input fan CFM) will cause cool
air to flow into the case across drive devices.

Read it again, Lane.
 
ric said:
Who said it does?

All I said is that having more exhaust fans than input fans (or more
accurately more exhaust fan CFM than input fan CFM) will cause cool
air to flow into the case across drive devices.

Read it again, Lane.
Click to expand...

Same CFM same airflow, Yes, No?

Lane
 
Lame said:
Same CFM same airflow, Yes, No?
Click to expand...

[sigh...] Yes, but:

If there is more *input* CFM than output CFM, warm internal air will flow
*out* over the drive devices.

If there is more *output* CFM than input CFM, cool external air will flow
*in* over the drive devices. This is why a low dust environment is
recommended
for this setup.

Comprende?
 
If there is more *input* CFM than output CFM, warm internal air will flow
*out* over the drive devices.

If there is more *output* CFM than input CFM, cool external air will flow
*in* over the drive devices. This is why a low dust environment is
recommended
for this setup.

Comprende?
Click to expand...

....Just my two cents...

a.) 100CFM in and 200CFM out = 100 CFM air movement (+any leakage into the
case, such as vent holes and floppy drive slots, etc.)

b.) 200CFM in and 100CFM out = 100CFM air movement (+ same leakage, except
it's from the inside out)

B is preferable to A because it does not draw dusty air from outside the
case through your floppy or CD drive (or any other hole in the case. With B,
you can filter the intake air and stop dust from entering the case.

What is MORE important is WHERE the air goes once it's inside the case...

For example, having a front fan blowing in and then a blowhole on the side
of the case over the PCI slots blowing out may rob a lot of airflow from
going over the CPU.

A good fan scenario is this...

Front fan blowing in. Blowhole over CPU blowing in. Rear fan blowing out.
Top fan (not many cases have this) blowing out. PSU should blow out. If you
can get an air intake over the PCI slots as well, blow it in. This will
force the cool air to cross the mainboard from bottom front to upper rear,
bringing cool air from the front and side of the case, blowing it over the
HDD, PCI cards and CPU, then sucking it out the back, and top (where the hot
air will want to go anyhow). Keep the rear of the case away from the wall so
you don't end up with heat buildup.
 
William said:
AMD recommends having your fan (or fans) blowing out at the back of the
case. That pulls the air through the case and over the CPU. I've noticed
that cases come set up that way these days, whereas a few years ago they
always had a fan in the front blowing in. That's the way I do it.
Click to expand...


AMD also recomends a PSU that draws it's air from the underside rather than
the front. This can have a big effect on CPU cooling.
 
ric said:
.... snip ...

If there is more *input* CFM than output CFM, warm internal air
will flow *out* over the drive devices.
Click to expand...

If this condition persists the internal pressure will eventually
explode the entire system.
If there is more *output* CFM than input CFM, cool external air
will flow *in* over the drive devices. This is why a low dust
environment is recommended for this setup.
Click to expand...

And if this condition persists you must eventually achieve an
ideal interior vacuum. Neither seems to be something to be
devoutly wished for :-)

The point is that in all cases equilibrium is reached, and air
flows from here to there. Both here and there are external.
 
Phrederick said:
...Just my two cents...

a.) 100CFM in and 200CFM out = 100 CFM air movement (+any leakage into the
case, such as vent holes and floppy drive slots, etc.)

b.) 200CFM in and 100CFM out = 100CFM air movement (+ same leakage, except
it's from the inside out)

B is preferable to A because it does not draw dusty air from outside the
case through your floppy or CD drive (or any other hole in the case. With B,
you can filter the intake air and stop dust from entering the case.

What is MORE important is WHERE the air goes once it's inside the case...

For example, having a front fan blowing in and then a blowhole on the side
of the case over the PCI slots blowing out may rob a lot of airflow from
going over the CPU.

A good fan scenario is this...

Front fan blowing in. Blowhole over CPU blowing in. Rear fan blowing out.
Top fan (not many cases have this) blowing out. PSU should blow out. If you
can get an air intake over the PCI slots as well, blow it in. This will
force the cool air to cross the mainboard from bottom front to upper rear,
bringing cool air from the front and side of the case, blowing it over the
HDD, PCI cards and CPU, then sucking it out the back, and top (where the hot
air will want to go anyhow). Keep the rear of the case away from the wall so
you don't end up with heat buildup.
Click to expand...

Sounds good to me, most newer cases have this similar scenario,
Front fan blowing in over hard drives
Back fan blowing in towards CPU
PSU fan blowing out,

This also results in positive case pressure.

Adding another fan blowing in to cool the cards is where many disagree with
me because I now have 3 fans blowing in and one blowing out, but as long as
there is adequate escape vents for the air I see no problem with it. An
additional vent hole can also be cut and a grill put over it but I see no
reason to add another exhaust fan as the air will be pushed out anyway.

Lane
 
Sounds good to me, most newer cases have this similar scenario,
Front fan blowing in over hard drives
Back fan blowing in towards CPU
PSU fan blowing out,

This also results in positive case pressure.

Adding another fan blowing in to cool the cards is where many disagree with
me because I now have 3 fans blowing in and one blowing out, but as long as
there is adequate escape vents for the air I see no problem with it. An
additional vent hole can also be cut and a grill put over it but I see no
reason to add another exhaust fan as the air will be pushed out anyway.

Lane
Click to expand...

If you want filtered incoming air it's pretty much manditory to have
double the fans (or larger sizes) blowing in than out, even if
positive pressure isn't obtained or even the goal... typically a fan
filter cuts airflow by at least 50%, +- depending on the filter
density and area.


Dave
 
Sounds good to me, most newer cases have this similar scenario,
Front fan blowing in over hard drives
Back fan blowing in towards CPU
PSU fan blowing out,
Click to expand...

You don't want this.. The back fan will cause two negative effects. First,
it will suck warmed air from behind the case (where the PSU vents) and
secondly it will push away the cool air from the front fan.
This also results in positive case pressure.
Click to expand...

This is the trick... using the front fan blowing in, and two rears blowing
out, and still keeping a positive pressure. That's why a blowhole in the
side would help, as would two front fans if you can get them.
Adding another fan blowing in to cool the cards is where many disagree with
me because I now have 3 fans blowing in and one blowing out, but as long as
there is adequate escape vents for the air I see no problem with it.
Click to expand...

Your rear fan should also blow out. Balances things and keeps all the hot
air going in one direction.
An additional vent hole can also be cut and a grill put over it but I see no
reason to add another exhaust fan as the air will be pushed out anyway.
Click to expand...

Turn your rear fan around and it will be close to balanced.
 
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