Quiet PCs, Ducting Air from Case Fan to Heatsink?

Milo_Mindbender asks: "While listening to the whine of my heatsink fan I was wondering. It seems like a good way to get quiet cooling for the CPU would be to mount a fan in the back of my case and run a duct of some kind (folded sheet metal or some kind of hose) from the back of the fan directly onto the top of a fan-less CPU heatsink. You should be able to get the same amount of airflow with a large slow (quiet) case fan as you do with a little noisy cpu fan...and the air being blown onto the heatsink would be cooler as well. This seems like a fairly obvious idea so I'm wondering if there's some reason why it wouldn't work, or if anyone has tried it and could tell us how it turned out." Yeah, but what about the heat in the rest of the system? Depending on the size of your enclosure (and what's in it), you may or may not need more than one fan. Has anyone tried something like this and can comment on how well it worked?

Comments

Already been done

[waytoomuchcoffee]

link

Dell did this

[bartb]

I have two dell PCs, the first is 4 years old, the second 2 years. They both use a plactic duct that is attached to a fan in the back and covers the CPU entirely.
The four year old is still really quiet, the other one is starting to make more noise. But that's because of a buggy fan on the video card...
-> maybe we can apply the same strategy there?.

I just looked at a similar thing

[MiTEG]

I generally leave my computer on, and recently I realized that the noise was nearly unbearable to those who were unacustomed to it. I also realized how pleasant it might be to have a near-silent system, so I took it upon myself to see what I could do to make my system noiseless.

I think the main problem with your plan is the amount of airflow required to properly cool a CPU with just a heatsync. Unless it is a Celeron300A or C3 or something of that nature, if you use a just a heatsync you'll need an 80mm fan running at least 2000 RPM. At that speed, the noise the air makes is quite noticeable, even if you choose to get one of the ultra-quiet brands.

I finally decided to just get a new heatsync/cpu fan combo for around $30 from QuietPC and I have to say that not only is it almost silent, it keeps my system cooler than the stock Intel CPU fan. The PSU is another source of noise, and I upgraded my 300W Antec to a 370W TTGI-350SS for around $40. TTGI isn't as well known a name as Enermax or Zalman, but I've found my PSU to be just as noiselss as advertised.

I don't want to discourage you, but I don't really consider heatsync/case fan combos viable for a silent PC with an Athlon XP or P4. It might be expensive to experiment, but then again having such a quiet machine is worth it. I take great pleasure in surprising my friends by turning my monitor on the show them that my computer is already on.