How many fans do I need?

I'm buying a case 2nd hand without fans (the case is a CM Praetorian). The case would otherwise come with 4 80mm fans on 4 fan slots. I was thinking of buying 4 fans and sticking them in its place, as since the case usually comes with 4*80mm fans, that is how many they recommend you using.

However a friend of mine just told me that I heat isn't too big an issue and I should me able to make do with jus 2 fans - 1 at front 1 at back, hell he even said 1 fan wouldnt really cause too many problems.

I'm buying a 3500+ and a 6800GT PCIE and 1 hard drive. I'm going to overclock the video card at the very least.

I realise the best thing for me to do is buy 2 fans and look at the temperature, and buy more if needed, but how many fans do you think I would actually need? Furthermore, CM desinged this case to run 4 fans, so not running 4 fans may disrupt the airflow, internal pressure, whatever. Will it?

Make sure to have equal air flow coming from the front of the case, side, and rear. Also, since your running a beefy system, just buy 4 80mm fans and put them in its place, also get the Nexus fan controller (The 3.5 Bay 1) and that should cool your system. 4 is way more than enough, even 1 80mm in the back is ok. Just get 4 fans with a fan controller, gl.

yep, positive case pressure is good, i have 4 in, 2 out.

I think it works out that for about 200W of heat dissipation inside your case, if your case has a free air volume of about 1 cubic foot, then it will take 4 seconds for that amount of heat to raise the temperature of the air 1C.

Therefore, to maintain case temps of 1C or less below ambient, you need to have 15 CFM airflow. Since you can get nice quietish 80mm fans that move about 30cfm, then one pulling and one pushing should be adequate for ventilating practically any case.

However, if you don't have a tidy case, and airflow inside it is, poor, you might then require more powerful or a greater number of fans to ensure adequate airflow in all parts of the case.

Also some people rely on airflow speed for local cooling of passively sinked northbridges, mosfets etc, which is why more fans might be desireable.

Proper planning and careful cable routing will however mean you can have a cool and stable machine with only 2 quiet 30CFM push/pull fans.

regards,

Road Warrior

Thankyou for your responses. Can someone explain to me how a fan controller works? Are they hard to set up? Does that adjust fan speed automatically while activly sensing temperature, or is it manual?