Adding a fan to medium tower - extract or intake?

I have a medium tower system which has just been upgraded from a Duron to
Athlon XP 3200. To assist cooling in general I want to add a second fan. I
have options of a 4" fan at front or rear. I have placed some filter
material in the front of the case to reduce dust intake - this works and
gathers a lot of dust/dog hair. I was going to fit a fan as intake to the
front panel mounting posiion with the idea that this would be less likely to
draw dust into the DVD drive. I have had a problem in the past with another
machine whre the powerful extract fandrew in dust wherever possible
including the CD drive and this caused me grief.
Questionis which is better - a rear mounted 4" extract fan or a fron mounted
4" intake fan?
Richard

 

Your 4" fan mount is probably for a 92mm standard size fan.

You should have it as an intake fan so that you have positive air pressure
inside the case, this will push warm air out and, as you've already
discovered, will stop dust being sucked into the case from every available
orifice.

The filter material you've placed in the front of the case will cause
resistance to air intake, hence higher temps. If you can you should try to
raise the base unit off the floor as much as possible, even a few inches can
make all the difference and then try to see how you get on without the
filter.

 

The filter material I use is a very loosely woven type. I ran the machine
for one hour with the filter in then one hour with it out. Temperature
samples with a probe near the centre of the case (away from the CPU fan)
showed less than degree difference and the CPU temperature was unchanged so
don't think the airflow is restricted too much. In fact most air is
probable entering the case through the unused rear panel fan aperture which
is only just below the PSU fan.
I will order a low noise fan from RS today.and run some tests. I also need
to measure the sound levels which are presently below the minimum range of
my SPL meter at 6" from the case (as long as I deaden the vibration of the
very flimsy side panels of the case). Next job will also involve finding
some damping material for the panels.
Richard

 

I'd go for the (filtered) front intake. You probably already have a rear
extract (look in the PSU!), and as you've noticed having dust sucked in
through every device with a slot in (CD, DVD, FDD, etc) is not a great
plan.

 

ferrymanr wrote:
[snip]
< Next job will also involve finding

maplins do sound absorbing sticky backed stuff...
http://www.maplin.co.uk/Module.aspx?ModuleNo=32290&criteria=sound absorb&doy=13m12
I've used this, it works quite well

Douggie

 

I have a recent Antec case (small midi tower) which has a permanent 3-speed
120 m/m fan fitted at the rear, and an optional 80 m/m one that fits in the
front. I only need to use the fan at the lowest speed.

Sylvain.

 

I fitted an intake fan to my case some weeks ago and am well pleased. The
case perforations were rather small and air whistling through them made a
lot of noise so I got out the hole cutter and made a full size hole for the
fan and fitted a wireframe fan guard. Much quieter.If anything the fan is
too efficient. It is connected to the three pin connector on my Gigabyte MB
marked SYS-FAN. I'm not sure if the MB is supposed to control the fan but
it seems to run at full speed all the time (what does the tghird wire do -
just senset he fan speed?). I am considering dropping the 12V supply to
about 10V to reduce speed and noise using my old method of three series
connected diodes giving about 1.8 to 2V drop.
Richard

 

Or 7v by using the 12V and 5V lines instead - that leads to less heat
generation inside the case and often gives you enough air flow.

Cheers - Jaimie