Kroma wrote:
> Hi,
>
> 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:
>
> http://tinyurl.com/2fle8k which is the correct size and has the correct
> connections.
>
> 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:
>
> http://tinyurl.com/3c35vq
>
> and like this from the inside:
>
> http://tinyurl.com/2qheg5
>
> 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!
>
> Thanks,
>
> Kroma

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.

http://www.tritechcoa.com/images/products/I87141.jpg

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.

http://images10.newegg.com/NeweggIma...129-018-09.jpg
(Shows fan installed in place.)
http://images10.newegg.com/NeweggIma...129-018-08.jpg

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
cool.

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.

Paul