Best Fan Setup?

Here's what works best for me. It builds up good air pressure and exhausts out the back

I agree. You should change the direction of the top fan so that it exhausts air out. Hot air naturally rises, so why would you want to force it back down? As regards correct airflow, my understanding of it is that it should be balanced, and in your case it very clearly is not. Fans should not be used to force air through a system, rather they should be used to assist the natural flow of air through it. A quick test of its effectiveness is to feel the temperature of the air from your exhaust fan with your hand, or measure it with a suitable thermometer, after several hours of running. Mine feels quite cool, but if it feels warm or even hot, then I would check the cooling arrangement and fan location/orientation/speed and make suitable changes so that the temperature of exhausted air is no longer excessive.

A simple analogy to your situation is a funnel. This has a wide reservoir that you pour water into, and a narrow spout from which it comes out. Upto a certain flow rate, water is able to leave through the spout at the same rate as what it enters the funnel at the other side. This is what you're aiming for. However, if you increase the speed at which water is poured into the spout, there comes a point where the flow balance is such that, although water is coming through the spout at a steady rate, it is no longer fast enough to stop a build up of water in the main body of the funnel. With a funnel, this simply needs to water overflowing. With air, as in the case of computer cooling, this leads to a rise in temperature as the air molecules are forced into a much tighter space than they would otherwise occupy. Thus, when the air finally does manage to exhaust your system it is already at a higher temperature than it should be, and that is before factoring in any heat that is generated by the components in the system.

See http://en.wikipedia.org/wiki/Combined_gas_law



From the above equation, it can be seen that in order to maintain the constant k at the same value the value of T needs to rise in proportion to the ratio of p and V. Since V is a constant (the inside volume of your system), T varies in direct proportion to p. Thus, as the pressure increases, so does the temperature.

Front to back air flow is generally the best, some fancier cases allow for you to divide the air flow up a little but I've generally found those cases to do so at the cost of airflow to some specific component that needs it.
The basic front to back works best in almost all situations. I also suggest keeping both front and back clear of objects, many people jam their computers into desks in one way or another and this generally leads to the hot air not clearing the back of the case properly and leading to heat build up over time especially if the machine is being used for any intensive process i.e. video editing/conversion, rendering, gaming etc..

To answer your original question, you should arrange that the front and side fans bring air into the case, whilst the top and rear fans exhaust it out. Size wise, you should be OK, but you might need to reduce the speed of the side fans slightly so as not to unbalance the air flow. You need to ensure that the volume of air flowing in equals the volume flowing out (see my explanation above).

monster528 said:

tw33k said:

Here's what works best for me. It builds up good air pressure and exhausts out the back

thats what i was thinking, but is the back fan strong enough to push out all the air? basically its a single fan moving all the air out. would it be better to put a stronger fan on the back?

I have an Ultra Kaze 3000 on the back. More than powerful enough

tw33k: That really seems like a lot of fans to me. I usually run with 1 front intake, 1 rear exhaust and 1 roof exhaust. Out of curiosity, do you see a massive temp increase if you were to shut off at least 1/2 of those fans? I'm just trying to figure out why some people run with just a few fans and others seem to feel that tons of fans are necessary. I've overclocked a number of machines, built at least 10 over the years, never put in tons of cooling and have never (as far as I know), ever had a heat related hardware death.

It's all about ACFM regardless of whether it's actually true in daily practice the ideal that the more air moved the better the heat is dissipated makes basic sense.
Actual cubic feet per minute - Wikipedia, the free encyclopedia

Of course most computer fans are just measured in plain CFM, same basic measure though.