Roof fan setup

[Verponian]

I know this may have been asked a lot in one way or another all over the internet but I value opinions on here so thought I'd pop a question in.

I recently did a stock take after various upgrades and the like and realised I had enough in spares and old parts to build a secondary PC. I'm now trying to improve a few cooling aspects in prep for some OCing.

I have a 2500k cooled by a Hyper 212 EVO in a Zalman Plus 9 case. I've ordered a pair of SP120s for my Hyper 212 heatsink and once the led version of the AF140s / AF120s come out, will buy some for the roof for the Zalman case.

Question is this: I was just going to set both roof fans as exhausts because hot air rises etc. However, as I have my heatsink set up vertically (air drawn in from front of case, passed out at back), I wondered if having both roof fans set as exhausts might effectively steal some cool air from my CPU cooler. Putting it another way, the roof fan closest to the front of the case would be exhausting cool air before it could feed into the CPU cooler.

Therefore, would it be better to set the front roof fan as an intake to feed air down in front of the CPU cooler or stick with dual roof exhausts?

I know the obvious thing would be to just buy the fans and test it myself but I was just wondering if anyone had any experience of it or could point out a way I was being massively dense without realising it.

 

[Make]

Use 1 fan as exhaust on the roof, leave 2nd slot open. The fan will be too powerful and it will blow right past the CPU cooler so it will starve it off air. Open slot leaves space for the air to do as it pleases.

My experience in an exact situation.

 

[RHS]

As a rule of thumb when air cooling you want positive air pressure inside the case, in other words plenty of air inside to get the cooling job done.

Having 2 exhaust fans will defeat the purpose and could lead to hotter CPU temps so it may limit the maximum OC you could achieve.

 

[doyll]

Case cooling is probably the most important part of an aircooled system.. and sadly often neglected. The below might be of interest.

Spoiler

The only way to know what works best in your case (no pun) is test different combinations and see.

There is much more to cooling than good cases, good fans and good CPU / GPU coolers. Modern GPU's make more heat than CPU... and getting that heat out of the case can be a challenge.

Setting up the case to cool properly is the hardest and most time consuming part of a build... And the most neglected by most builders.

Cases, especially those with filters, usually benefit from fans with higher static pressure ratings than stock fans... "cooler" fans instead of "case" fans.

Intakes are typically more restricted than exhaust; air filter, more restrictive grill, HDD cage, etc. I prefer a little more intake than exhaust.

And don't confuse number of fans with amount of airflow... or cofuse airflow with airblow

Airflow is flowing cool air from intake to component and flowing hot air from component out of case without the hot air mixing with the cool air.

Airblow is lots of fans blowing air with some of hot air from components mixing with cool air making it warmer resulting in warm air not cooling components as well as the cool air will.

Putting fans in case as intake and/or exhaust is only the first step. These fans only move air in and out of case.

This does not mean heated air is not mixing with cool air.

Nor does it mean cool air is going to where it is needed.

Getting the air to flow inside of case properly is even more important. We still need to manage where the air flows inside the case. We can do this several ways; deflectors, cooler intake fans, exhaust fans, removing vent grills, using fans with higher pressure/airflow, building ducts to or from CPU/GPU cooler, etc.

Using a remote temperature sensor to monitor what air temps are is the key to finding out where the cool air is flowing and knowing heated air is not mixing into it. By monitoring this we can than make changes to get airflow the way we want it.

I monitor the temps with a cheap indoor/outdoor wired remote or terrarium digital thermometer. Twist a piece of stiff insulated wire into the last 8" of sensor lead so you can bend it to position sensor where you want it... like 40mm in front of your GPU cooler/radiator intake.. to see what the air temp going into CPU / GPU cooler is compared to room temp. The closer it is to room temp the better.. Shouldn't be more 5c maximum, 2-3c is what I usually end up with after 30 minutes full load on both CPU and GPU.

Spoiler

 

[Make]

As a rule of thumb when air cooling you want positive air pressure inside the case, in other words plenty of air inside to get the cooling job done.

Having 2 exhaust fans will defeat the purpose and could lead to hotter CPU temps so it may limit the maximum OC you could achieve.

That depends. Negative pressure is just as good at cooling, you just need to have a proper case for it. It might be more dusty, but it also offers you less possible hotspots when the air is sucked out, not "left to leave and circulate".

Most cases come as negative pressure by default (2 exhausts, 1 intake), and also the evga Hadron is entirely based on negative pressure only. (2 exhausts at top).

It's all good as long as you've designed it properly

I have no idea whether mine's neutral, negative, or positive, so many different fans and speeds. However changing the case fan speeds at any point except the H100i don't affect temps at all, so I guess thats a good thing..

 

[doyll]

Case only lets as much air out as there is coming in... or only lets in as much as is going going out.. Exhaust fans pull air near them out and sometimes that removes a 'hot spots', but by the same token intake fans blow air in and and that can also remove 'hot spots'.

'Positive, negative, neutral' don't cool the case. How much air moves through the case and where that air flows while inside the case determine how well it cools. One thing that cannot be disputed is we need more air flowing through the case than the CPU and GPU cooling fans use. If not, they eat their own heated exhaust air.

Many cases come with 2 intake and 1 exhaust too.

 

[Verponian]

Though I know it's a pretty imprecise way to do it, the general rule I was trying to run with was having a higher combined CFM of intake fans than exhausts in order to roughly get a positive pressure case (just because of dust).

In the same case, I was going to use a 140mm Akasa Apache as a front intake, a spare 120mm fan as a floor intake and a corsair af120 as rear exhaust. I know I could do without roof fans if push came to shove but I admit part of me wants to try out the AF140s and I'm looking for an excuse to use one or two of the new LED versions.

I was planning on getting a better fan controller with some temp probes so I might do some experimenting with a couple of the zalman 120 fans in the roof.