My new computer has a side vent that takes air to the CPU and this vent has no filter. This seems to now be universal. I could find a case with filters for the front fan but not the side vent.
My front filter after 12 months is shown below and shows that dust is a problem.












Recently a friends computer (no filters at all) with a pentium 4 3000mhz started slowing down and eventually stopped when doing intensive tasks.






You can just imagine how the fluff has packed the cooling fins below the fan.



Cleaning this part of the computer is not easy and I decided to do something about preventing it on my own computer.





Any filter placed over the side vent will have to offer very little resistance to air flow. Most fan filter frames you can buy are designed to work with the direct air connection from a fan and the full suction of the fan is available to drag air through the filter. This is not the case with the side vent. The side vent is supposed to have its internal extendable inner air guide positioned 12 to 20mm from the top of the fan (see Intel Chassis Air Guide V1.1  Sept 2003).

Note that  the correct positioning of this guide seems to often be overlooked when the computer has been assembled by smaller commercial system builders. In both of the computers mentioned here it was not extended at all..



This is the trace from SpeedFan showing parts of two identical runs of Orthos stress test. The LHS is with the air guide fully retracted and the RHS with the air guide positioned 16mm away from the top of the fan. The test shows about a 2C improvement in the CPU temperature. The inlet temperature at the time was 22C and the exit temperature at the peak 26C.  The case was to the Intel 1.1 air guide standard and was fitted with 120mm front and rear fans. Less well ventilated cases may benefit more from the correct positioning of the air guide. One simple way of checking the air guide to fan clearance is to place the end of a rule on the top of the fan and sight across the case edges. You can confirm your measurements are correct with the simple tool below.






Make something like this, then to check that you have the air guide set correctly pass it through the air holes in the case (from the inside) and with the case side back on, push it onto the top of the fan and mark the stem where it exits the case. If you have placed some graduations on the card you can read off the clearance by sighting across the air guide with the mark set.



Warning. The filter described below may cause your computer to overheat and the following description is only a report of what I did and not a recommendation that you should follow. If YOU decide to try something along these lines you should do your own temperature tests to determine its suitability and take all the responsibility for any problems upon yourself.

Two things are needed to make a filter—some kind of filter material and a frame of some sort.
I  have been on the lookout for some sort of filter material  and bought various things that caught my eye. Chux cleaning cloth was given a try but proved to restrictive. I recently noticed that my daughters cloths drier had a fine nylon mesh filter (ours uses foam). Googling revealed the suggestion the womens stockings could be used. I tested a 15 denier stocking and found it had very little air resistance and a .5mm triangular weave. The nylon mesh on my air conditioner filter is 1mm square so it seems reasonable choice.

 

15 denier stocking weave with 1mm ruler marks in background.



As a test a section of stocking was just taped across the vent. This is far from optimal as the filter area being used is only as big as the actual holes in the vent hole area.
I saw a  Short round CD/DVD container and knew I was on to something.





Cutting some way in from the edge gives the frame some strength.












This is fiddly and I had to resort to a rubber band.











Electrical tape went over the rubber band.











The base of the CD/DVD container was cut out with a fret saw and holes drilled  for the mounting screws.
There was a flange on the underside of the base that was just where the holes were to go and that was removed so the drill would not be pushed off center.
The ring could be more easily mounted with double sided tape or blue tack.













The air guide showing how it can be extended.

The special self tapping screws that had held the air guide were too short to mount to the filter base. I have seen longer ones available but instead used bolts that passed through the existing holes and will enable the original screws to the reused if the case is returned to normal. Nuts tend to come loose and can kill a computer so I painted on something to prevent that occurring.







Here is the finished result.It will look a lot better on a black case I am sure.
Taking the filter off to clean is a simple twist.
I can see fluff building up on it after a few days but its performance will require more testing.
I can not detect any rise in temperature when it is fitted after 15minutes of 100% processor load.
If the stocking filter is not your preference and you have access to something better like special low restriction filter foam, it could be made a press fit into the recessed top of the CD/DVD container.  With a limp foam you  could cut out a pattern into the top of the container to give support to the foam. Note, the filter needs to offer little resistance because the air giude (snout) when correctly positioned  is not a tight fit to the CPU fan.

The graphics card air vents below remain uncovered until I can find a frame.
My graphics card has no fan so I can get to the heat sink to clean it easily but at least now the hard to clean CPU heat sink is getting mostly filtered air.By the way. The amount of dust is proportional to the amount of air that flows (and the environment). If your computer sits for long periods with the fans running when it could be in sleep mode all you are doing is wasting electricity and adding dust to the inside. Setting your power saving options and even variable fan speed if it is available could make a huge difference to the dust build up.

Tests on my over clocked (2400MHZ) E2140 CPU @ 100% on both cores showed less than 0.5C rise with the stocking filter as shown.








Air conditioning filter manufactures are a source of filter material. This is a mesh filter that has approximately 1mm openings and attracts dust by becoming electro statically charged. The material has a 3D profile so keeping it away from the surface of the case to increase the area of air flow is not quite so important. It is quite stiff but will fray at the edges unless something is done to prevent it. Painting the edges with nail polish should do the trick.












The hook side of self adhesive velcro attachers well to the mesh and it could be placed all around the vent. The mesh is then easily removed for cleaning.

If you can get this material you could incorporate it in the "CD" mounting above for the least possible restriction or dispense with the "CD" method and just velcro a patch over the CPU vent hole.









To test how stocking compares with a commercial filter it is necessary to ensure that the same amount of air flows through each.
I took a section of the commercial filter and fixed a square of stocking on each side so that air had to pass through in one area stocking then filter and in another area filter then stocking. Simply put stocking was on the front in one area and on the back in another. I set this at the back of a pedestal fan and went dust hunting with a hand broom. the dust was dislodged from the broom and carried through the filters. Visually, the stocking collected just as much dust as the filter. However a closer look at the commercial filter at 10 X revealed that the electrostatic feature was working, see below. Very little of the lint type dust passed the stocking and was collected by the filter underneath (see picture) which is confirmation that the stocking was doing a reasonable job.

Because it has a flat surface the stocking may become clogged sooner than a commercial filter material but this is easily seen and cleaned in this application.








From this picture of the rectangular side vent filter after a few days of use, you can see that the commercial filter material traps and holds very fine particles that would easily fit through the holes in the weave. I would presume electrostatic attraction plays a part in this. Stockings that were anti static treated would not attract fine particles in this way and the fine threads used may not hold them.

Some of this material was placed under the stocking in the round holder above for a long term test. This revealed that a stocking is not that effective as it passed about 50% of mostly finer dust.


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