N. Thornton said:
To run fanless you'd need a heatsink several times the size of whats
there already. You'd probably cook your CPU. Having said that, I had
one PC that ran with no CPU fan, some will.
There are options that do not produce noise, you have to transfer the
heat to a large heatsink mounted onto the case.
One possibility would be a heat pipe, which uses an easily evaporating
liquid to cool the CPU. The steam condenses at the heatsink and dribbles
back to the CPU, where the cycle starts again. A hog to design, probably
out of reach to hobbyist. Some notebooks use that sort of device.
The second way is to use water cooling. The CPU, chip set and graphic
card processor heatsinks are replaced by small devices, through which
water flows. The hot water then is cooled at the case-mounted heat sink.
The stuff is commercially available in kit form (about 200 euro). Since
water has a much higher heat capacity than air, the loud, fast blowing
fans can be replaced by a almost inaudible aquarium pump. There are
special power supply units available for use in such systems, so you can
make do without the fan in there as well (another 150 euro or so).
Whether that's worth if for a comuter that, judging by specification,
must be about 4-5 years old, you have to decide yourself.
If you do not want to spend that amount of money, you can buy large,
hence slow-turning, high quality fans with special bearings (e.g.
Papst).