Last night I tried putting in a makeshift duct which routed air from outside the case directly onto the CPU...

A couple of months ago I was also looking for the ultimate cooling solution for my Pc. That's why I ended up with watercooling, but I did try it with multiple fans first.

I came to the conclusion that is was generally a better idea to remove heat by blowing the hot air out of the PC than by blowing room-temperature-air into the case.

I first tried this by making a smal tunnel through which the heat from the CPU was directly blown out of the case, so that it couldn't add to the temperature inside the case. I used those paper toilet rolls for that. Worked pretty well, but it could be improved.

I also had another idea, that I could do a pairs of quiet 40mm fans in certain spots on the case that don't accept an 80mm fan. I remember seeing somewhere an ad for a very quiet 40mm fan, I'll see what I can come up with.

I wouldn't do that if I were you. No matter how "quiet" these little fans are supposed to be, they will ALWAYS be more noisier than their bigger brothers. The reason is simple : a small fan has to rotate faster to move an equal amount of air as a larger fan, and thus tends to be noisier.
It's for this reason that I modded my case with a dremel tool so that 120mm fans would fit. The ideal setup is one 120mm fan on the front bottom of your case blowing fresh air into the case and one 120mm fan at the back pulling the hot air out. That way you get as sort of "continuous air flow" through your case. That, combined with a good CPU cooler will give you the best results.

Of course, not all case can be equiped with 120mm fans, not even after using a dremel tool on them. In that case I woud still advise you to use 80mm fans where possible, and avoid small fans as much as you can. Adding lots of little fans to your system WILL increase the noise it makes tremendously, even if they are so-called "silent fans".

I'll add a few pics of my setup to show you what I mean.


This is the backside of the case. You can clearly see the big 120mm hole that I made with the Demel tool. Through the hole you can see the other 120mm hole I made in the front of the case.


This is the big hole in the front of the case up close.

This is with the 120mm fan on. The fan is a Vantec "stealth" fan, supposed to be very quiet. (and it is). You can also see the pump and the reservoir of the water cooling system. The big black thing in the upper left corner is the radiator.

I'm very pleased with the result. The mod is invisible (because there's still a metal and a plexi plate with holes in it on the front of the PC) and performs very well. Also, because the fan is also behind the harddisk tray, my harddisk stays nice and cool.