Case fan installation

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I've just had to replace my PSU after the last one started smoking.  My new
PSU only has a single fan (the last had 2) and as a result I've noticed that
my PC temperatures are up.

My motherboard goes up to 41C and the CPU to around 61C when in use.  I have
a Pentium4 2.66

So, I've decided that a case fan is the way to go.

I've chosen a fan: which is the correct size and has the correct

However, having looked at the rear of my ATX case I'm a little unsure - I
was expecting lots of holes or a removable section - but I have some grilles
(marked 'Dual fan system').  The lower grill is for a 70mm fan and the upper
for an 80mm (the one I've chosen, right)?

The case looks like this from the outside:

and like this from the inside:

Note that the grilles have a kind of metal canopy over them - I presume to
prevent dust ingress?

So - how would I fit the fan?  Do I simply hold it against the inside of the
case and screw from the outside?  The picture of the fan shows a 'layered'
surround of the fan - are the screws really long and they simply screw
through the case, through the first layer and then the second?

I can also only locate 2 holes (and that's all they are - holes) for screws
I presume.  Will that suffice?

Or am I wrong and I need to remove something (there doesn't seem to be
anything to remove though).

I'm sure it's a very simple job but I don't want to make a silly mistake!



Re: Case fan installation

Kroma wrote:
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The sheet metal pattern shown in your pictures, resists the flow of air.
Bolting a fan to the two spots intended for fans, would result in a
less than spectacular airflow. In other words, the fan would make a
noise, but no air would come out the back of the computer.

You could cut and remove the material, leaving a circular hole. The
circular hole will mate with the fan, and leave low resistance to airflow.
That sheet metal is thin, and the problem will be, finding a tool that
can do a neat job of cutting the metal, without distorting or
damaging anything in the vicinity of the work area. (The metal is probably
too thick to cut easily with a nibbling tool, and a jigsaw would need a
metal cutting blade with fine teeth on it.) Before you start cutting a
hole, you'd have to strip all hardware out of the computer case, and then
vacuum out all the little metal bits, after the cutting is finished. You cannot
leave any metal filings inside the computer case, and that is why all the
hardware has to come out, before you start cutting.

Once the hole is cut, you can place a wire fan grill like this,
over the hole. The screws you get at the hardware store, to mount the
fan, should also extend through the holes on this grill, and hold the
grill in place. The grill would have to go on the
outside of the computer case, for best results. You can buy extra long
screws at the hardware store, and then cut the excess length off the
end of the screw, using a hacksaw. If you leave the nut in place on the
screw, and hole the nut and screw in a vise, you can file the metal burrs
off the end of the freshly cut screw, making the screw the exact length
needed for the job.

An alternative, would be to buy a computer case with visibly better
ventilation. Some computer cases come with lower arrestance grill covers
than the ones on your computer case. This one, for example, has hexagonal
holes punched in the sheet metal, and is almost as good as using a
wire mesh grill.
(Shows fan installed in place.)

If there is a mounting position for a fan on the side cover of the case,
you could use that location to house a fan. That is less convenient,
due to the wiring.

As for the fan you pictured, that fan has a relatively low rating, and is
quiet at the same time. In a given fan family, the fans come in low,
medium, high, and ultra capacity. Medium might correspond to 35 CFM.
High might be 60 to 72CFM or so. High is probably too much fan for
your computer. But low may not be enough to be effective.

I use a 110CFM fan on my current computer, but the fan is fed by
a variable speed control, and runs at a reduced speed. The fan is too
much for the application, but I'm using it anyway. The case air is never
hot in my computer case. (The PSU air is warm, but not the case exhaust.)

And what you are most worried about cooling in your computer case,
is the hard drive. The hard drive, by specification, has the lowest
tolerance to heat, so if you want to add cooling, the hard drive is
the thing that needs cool air. The other components in the case
can take a bit more heat. The life of the electrolytic capacitors
on the motherboard and inside the power supply, is reduced by the
heat, but with the hard drive, the issue is you might lose all your
user data, while other parts of the computer can be replaced if
something happens. So your first priority is to keep the hard drive

And to answer one of your questions - yes, you do hold the fan against
the inside of the case. The raised metal on the screw holes, should
cause the fan to clear the metal of the case. You can spin the fan
blade with your finger, before powering the computer, to check that
the fan blade is not dragging against the metal.


Re: Case fan installation

Kroma wrote:
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Isn't that rather violent?  There are smoking cessation pills
and/or patches available :-)

Chuck F (cbfalconer at maineline dot net)
   Available for consulting/temporary embedded and systems.

Re: Case fan installation

On Tue, 30 Jan 2007 23:51:29 -0000, "Kroma"

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OK, but  are they now TOO high?
If not too high, you are done.

Otherwise, it is a bad idea on a semi-modern system to rely
on the PSU for much of the airflow, that's what the rear
chassis fan's purpose is.

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What does "In use" mean?  The relevant temp is at full load,
running Prime95's Torture Test for 30 minutes THEN taking a
reading, for example.  You'd then compare this to the prior
temp under the old PSU configuration... which you may not be
able to do, but the key is how hot it gets at peak, now.

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You didn't have a case fan yet?
If not, yes you should('ve) had one already.

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It also has fairly low RPM/airflow, which is good for
limiting noise production, but also means lower airflow.  On
a modern system I'd use two of those on the rear of the
case, or use a different case.  Your needs may differ.

Those transparent fans are also more rigid than their black
counterparts and will transmit more vibration to the case =
louder when all else is equal.  We can't know exactly how
well balanced they are, which is also quite important, but
at least with their relatively low RPM the resultant
vibration shouldn't be very bad if they are of reasonable

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First, it looks like the replacement PSU is bad, I mean
junk.  I could be wrong but felt it may be important to
mention now.  What make, model and 12V current does it
support, and what are all the major parts in the system?

As for the rear vents, they're almost worthless.  The case
isn't usable like that, I would either replace the whole
case or strip it down (take out all parts) and cut out fan
holes for two of the above linked fans or as mentioned, two
equivalent black (plastic) ones.

Since the rear has such poor exhaust area, it wouldn't
surprise me if the front isn't much better, but I suspect
I'll see that with the below link.

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I was hoping for an inside view of the front wall of the
case, but a comment about that rear- it "looks" like it is
for 80mm fans, not big eough for 92mm unless you ignored the
original holes but that would be a more difficult way to cut
out that area so I still suggest 2 x 80mm fans, and of
course you'll need at least 4 screws, but personally I'd
drill out the holes to use 4 screws per each fan, 8 total.
By having all 4 screws you will possibly reduce vibrations
between case and fan frame, get a better seal between fan
frame and case wall (especially if cutting out the holes
makes the metal somewhat less planar afterwards), and
strengthen the area some with two larger holes in it.

It is theoretically possible to take some pliers and bend
those slots up a LOT, increasing the exhaust area exposed
behind the fan, but the resulting airflow will still be a
lot lower than cutting them out entirely, and it might be
noisier to keep them too.

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Perhaps that was the idea, but most cases don't have this
canopy design.  Since you didn't have fans installed it was
actually better (until now, since you need fans for a modern
system) that the holes be more restrictive to airflow, as
otherwise it would have created a short loop that interfered
with more passive intake through the front of the case.
Hence what I'd hoped for previously, a picture of the inside
front of the case as the rear fan effectiveness at
exhausting air depends on how well it can draw air in - and
in the front is best as the air then passes over the most
parts, may be the only method of cooling the front drive
rack and often the motherboard chipset.

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Yes after you cut out the hole or use the pliers to increase
the slit open area.

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You only need to screw through the first "layer" of the fan.

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Well it's a lot better than only one... but they should've
used 4.  You can try it with two, but I'd go ahead and drill
out the other 2 holes per fan, while the parts were out,
after cutting out the hole.

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It should've been simple to install a fan but that case
isn't designed very well.  You could just put a fan in as
you suggested and see how it does, but it would do a lot
better with the methods I've described above.

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