New build: Fan Direction

[Dresden]

Heya-

I finally finished my most recent build, and so far it's awesome. However, I'm concerned about heat. Especially since I have two GTX 580's running in an SLI setup. I went out and bought a 120mm case fan and installed it on the window, to blow directly on my video cards. I've supplied a few pictures of my computer to show the fan locations and I'll explain their direction. My main question is which direction should the 240mm fan on the top of the case face? Should it be blowing air into the computer or acting as an exhaust. I can drop the temperature significantly if it's okay to blow into the case, but then I worry about whether or not I have enough fans acting as exhaust.

I have an Antec Twelve Hundred V3 full size tower. There are 2x120mm fans on the rear of the case (outtake), 3x120mm fans in the front (outtake), 1x120mm aftermarket fan on the window blowing directly on my GPU's, and 1x240mm fan on the top of the case (outtake):

Which direction should these fans be facing to maximize airflow? Would it be a good idea to turn around the 240mm fan?

Thanks-

Dresden

 

[hoho]

Generally you should have roughly equal air flow going in and going out. If you have too big imbalance they won't work as well and airflow will be pretty bad. For inflow you should put the fans at front-bottom, though that one blowing on the GPUs should work too. For outflow they should be in the upper back and top of case.

I'd probably make the all three front fans+side one blowing in and everything else blowing out. Not quite balanced but should be good enough.

 

[Bouncing Zabaglione Bros.]

I agree with Hoho. I would put the three on the front and the one on the side blowing in, and the ones on the top and back blowing out.

Ideally you want the GPU fans blowing out the back of the case (I don't know if the GTX 580 has an exhaust shroud), and the CPU cooler blowing to the back or top, though I'd guess that radial fan style cooler doesn't really have a particular direction.

 

[digitalwanderer]

I'd probably make the all three front fans+side one blowing in and everything else blowing out. Not quite balanced but should be good enough.

Yup, that's exactly what I'd do too. The PSU will help a bit with the exiting air, as will any crack/screen in the case. Always better to have a bit more going in than out.

 

[AlNom]

Cold air goes in at bottom and front/side, hot air rises at back and top. Simple.

 

[Davros]

North east is my favourite fan direction

 

[Pete]

Dresden, I can't quite make out what's in your pics. Can you make them any bigger? ;p

 

[Grall]

Cold air goes in at bottom and front/side, hot air rises at back and top. Simple.

Convection doesn't work on moving air, like in a PC case full of fans.

Generally, it seems positive airflow (more in than out) gives lower temps than negative. It also gives better control over how air moves inside your case, and allows you to filter the air for dust.

 

[Dresden]

Dresden, I can't quite make out what's in your pics. Can you make them any bigger? ;p

Ah, they're pictures from my phone. I should probably scale them down next time I plan on posting pictures on a forum.

Good advice, everyone! It seems the factory direction of the 6 fans pre-installed is the general consensus, so I don't think I need to change anything. I wound up moving my HDD's, which were located parallel to my GPU's and the temperature dropped significantly. I also did some cable management to improve air flow. That Antec Twelve Hundred is sick. Both side panels are removeable, and there's enough space in the right side to fit a bundle of cables in it, then cover it with the panel.

On a GPU related note, are there any programs available to determine PCI speed from your expansion slots? I thought Nvidia Inspector did it, but apparently it doesn't. My stupid motherboard isn't very clear which slot runs at which speed, nor is the description in thw manual. I've even read someone complaining his SLI configuration didn't run at x16. I uses an Asus P8P67 WS Revolution.

 

[Silent_Buddha]

Generally, it seems positive airflow (more in than out) gives lower temps than negative. It also gives better control over how air moves inside your case, and allows you to filter the air for dust.

This is the best advice. Especially if you make use of dust filters. Positive pressure is always better than negative pressure and in most cases better than equal active intakes and outputs.

Having equal active input and output of air will allow for more directed airflow at the expense of more dead space (or turbulent air where most of the air just circulates within the case) and isolated heat islands. Positive pressure (as long as there are vents at key places) negates/minimizes this dead space as air is escaping out of every possible vent.

You can see this with many of the best cooling cases on the market. Take the Raven series of cases by Silverstone for example. One that I just recently purchased for a WHS machine has 2x 180mm fans at the bottom drawing air in with only 1x 120mm fan at the top drawing air out directly above the common CPU location (to allow for using Fanless heatsinks). Even the PSU is located such that it does not contribute to airflow/pressure in the case. It draws air in either from below or from the side of the case, and immediately expells it out the other side. A plethora of key vents means there is airflow over pretty much every single component. If you add fans to the case, it is advised to have them drawing air in rather than exhausting air out.

If you look at well designed server/workstation class cases, you'll see the vast majority don't even have exhaust fans. They are mostly fitted with just intake fans nowdays. Better cooling and dust control (as long as you use dust filters). My Sun Micro workstation has 3x massive 200mm intake fans, and that's it.

Regards,
SB

 

[Blazkowicz]

a rule of thumb I read many years ago stated that more exhaust than intake is preferable.
the reason given was, it gives more incentive for the air to exit the case, which is what you want for actually cooling.

but back then we only had to cool the CPU, cards were not heating much, and I guess it made sense when choosing between a rear fan and a front end.

 

[Silent_Buddha]

The biggest benefit for greater exhaust than intake is that YOU get a bit more control over airflow. So yes, back in the day when heat was mostly concentrated in the CPU's (overclocking) then later HDD's (7200 rpm HDDs used to be hot as hell) and to a certain degree Video cards (which didn't output nearly as much heat as even today's mainstream/upper tier budget cards) directed airflow was good enough. Chipsets were generally cool. Memory was generally cool. So you really only needed to make sure that the CPU was cooled efficiently and that excess heat didn't build up.

But even then, proper exhaust vent locations combined with positive pressure can achieve similar results.

Nowdays everything outputs more heat. Although with the exception of Video Cards and memory most components are a little cooler than they were, say, 2 years ago but probably still not as cool as they were over a decade ago.

And, of course, the greatest drawback of negative pressure created by exhaust being greater than intake is that you have very little control of where air enters the case unless you make use of airtight seals on all panels and do not have any open vents without dust filters. Then again, if you don't use dust filters on your intakes, that's a moot point and dust bunnies will build up regardless. And dust buildup will defeat any sort of cooling you can come up with.

Regards,
SB

 

[Grall]

With underpressure in the case, your power supply and graphics card blower(s) (if applicable) have to compete with case exhaust fans for air, this reduces their efficiency and in the case of temperature-sensitive fans, cause them to revv up and create more noise to produce similar cooling effect.

In the past, an exhaust fan (at the CPU) might have been preferable, but then, PCs did not burn quite so much power as they do today. I remember a time when a 400W power supply was considered monstrously oversized to a point that was just uselessly ridiculous. Today you can put together a box that burns upwards of one and a half kilowatts, and suddenly things seem a little different than they did in years past...

 

[swaaye]

I really like the cases that put the motherboard at the top and the PSU at the bottom. They tend to have large fans at the back and top and this pulls the rising hot air out very effectively. The PSU gets to breathe cold air from the bottom instead of the hottest air in the case. I've found this setup to be clearly superior to the traditional PSU-at-top design.

The pressure argument is a tough one. A lot of modern cases have so much venting that it isn't much of an issue anymore. But it's of course very difficult to predict where the air in the case will flow on its own so directed fans are useful in some cases. An inlet fan in the front of the case is good for the HDDs, for ex.

 

[Vadi]

Aren't these big fans performing badly compared to smaller ones? I do use 14cm fans but when I checked specs they were supposed to move as much air as the 12cm sizes.

I use two 14cm intake fans which cover almost the entire front of the case, and they even drop GPU temperature at 600RPM. There are no exhaust fans but the case has holes everywhere (Revoltec 60 3 ).

 

[Grall]

Larger fans can produce similar airflow to a smaller fan using lower RPM, meaning less noise. They typically have worse static pressure though (meaning they perform worse with resistance to airflow), so your real-world results may vary.

 

[RudeCurve]

I use two 14cm intake fans which cover almost the entire front of the case, and they even drop GPU temperature at 600RPM. There are no exhaust fans but the case has holes everywhere (Revoltec 60 3 ).

That makes sense as you have two fans. Also remember that psychoacoustically, sound is not cumulative in amplitude only in frequency. That means that if you have two identical fans spinning at the same speed the sound level output that you hear is the same as if it were a single fan. Louder sounds drown out quieter sounds so even if you don't hear those two low rpm fans you'll still hear the loud GPU fan(s).