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Proper fan config....

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DarkMask

Member
I had an idea... and it also has to do with a question of mine. I was wondering what the optimal configuration for fans was? I just reconfigured it so my back exhaust fan is now an intake fan, becoz it is so close to the processor and it seems like a negative airflow is created and creates more heat. But I was looking on AMD's site and they said that exhaust was the way to go in the back, and have intake on the front (which does make sense). I was just wondering what the best config was, and thought maybe u (the forum posters of anandtech) could list the best configs for different fans and fan placement configurations. Thanks
 
i think intake in the back is not good because the air coming in would be heated because it is under the powersupply. plus the intake in the back would be in the middle to the top of the case because the bottom is reserved for the PCI and AGP cards. since heat rises, its easier to remove it from the top of the tower than push it towards a low placed exhaust, as in the reverse setup you describe.
 
Proper air flow is what's important. By making the back fan into an intake, you are creating a loop in which air coming in from the back fan is sucked out by the PSU fan, which will then get sucked in again through the back fan. Not the best in cooling. However, by making the back fan the exhaust, air flows from the front of your case out through the back. You are again making a loop, since the air returns to the room, but a much bigger loop in with heat is allowed to dissipate more.
 
Intakes go low at the front of the case, exhausts go near the top at the back of the case. This way, cool fresh air is blown into the case at the bottom and rises both due to it taking heat from hot components (hot air naturally rises above cold air, heat convection) aswell as the draw from the top-rear fans which suck it out.

If you do it the other way around, the fans are working against natural heat convection. Also the heat from your CPU (easily the biggest heat provider, well maybe except PSU - which is also heating the air in that area) would be getting blown right back into the case, rather than sucked straight out. Always consider the air currents when adding or changing the fan setup in your case 🙂

BTW try to make volume of intake & exhausted air roughly equal, so if possible have the same model of fan (or fans rated with similar CFM)at each end. Some people make the intake a little stronger which preassurises the case slightly. This means all the little holes/spaces in the case blow a tiny amount of air out, so all dust goes via the intake fan which you can add a filter to. With more exhaust than intake, its the other way round and you'll notice all the little holes (PCI slot spacers, spaces around external drives fronting) start accumulating dust 🙂. There's probably an effect on the heat transfer qualities of e.g. HSF aswell, but not sure which way round and probably insignificant anyway.
 
Originally posted by: Davegod

BTW try to make volume of intake & exhausted air roughly equal, so if possible have the same model of fan (or fans rated with similar CFM)at each end. Some people make the intake a little stronger which preassurises the case slightly. This means all the little holes/spaces in the case blow a tiny amount of air out, so all dust goes via the intake fan which you can add a filter to. With more exhaust than intake, its the other way round and you'll notice all the little holes (PCI slot spacers, spaces around external drives fronting) start accumulating dust 🙂. There's probably an effect on the heat transfer qualities of e.g. HSF aswell, but not sure which way round and probably insignificant anyway.
Click to expand...

wouldnt a stronger exhaust than intake improve cooling? if a strong intake cause the pressure inside the case to rise, wouldnt a stronger exhaust cause the pressure to drop. and according to the ideal gas law of P * V = n * R * T, low pressure directly relates to lower temperature.
 
I did a few tests on my Dragon case to verify those specs by AMD, and believe it or not, the setup that AMD/Intel, everyone recommends, is basically the best for air cooling. I still prefer the idea of having the computer in a fridge 🙂
 
Actually, with my Fong kai FK-320 case, the 92mm rear fan is an intake by default. Then, with the addition of the shroud, it blows cool air directly over the CPU, and keeps the CPU very cool, especially compared with the rest of the case. However, this makes the rest of the case very warm, as only thre CPU is being fed cool air, and creates enormous positive pressure, since only the PSU is exhausting the hot air. However, this set up is working perfectly for my server at the time being, albeit with the addition of a 7-Volted 80mm fan to help exhaust the hot air.

The other problem with this is that if you install a front fan, it would only make sense to set it as an intake, since there is nothing down there generating heat, and it would do no good since hot air rises. So, once you install a front fan, you have incredible positive air pressure, and it completely disrupts the airflow in the case. So, if you do have a front intake fan (an exhaust would be silly in the front), it is logical to have a rear exhaust fan to create a nice stream of air and create more equivalent air pressure.

Since this is the way most cases work, it is usually best to have the rear fan set as an exhaust. However, if you have some other exhaust fans, say a blowhole in the top, and can match airflow reasonably well, then you could have both the front fan and the rear fan as intakes, and your CPU would be very cool. If you're not careful though, you can severely disrupt your airflow and make things worse.

Also, there are benefits to both ways... Having the rear fan drawing in cold air does give the CPU a fresh supply of cool air, but at the expense of other components in the case. Having it exhauist hot air keeps said air from collecting around the CPU, and keeps other components cool, but the CPU is a bit warmer. It's a give-and-take, and in most cases, the rear fan works better when its exhausting.

BTW, neither positive nor negative pressure is better. It is best to have equal airflow throughout, and people will tell you one way or another, but they both have adcantages and disadvanteg. Positive airflow keeps dust out better, but negative airflow draws the hot air out quicker. Equal has the best of both worlds 🙂
 
I have now done both, and I can positively conclude that exhaust is best in the back. Thanks for all the help people.
 
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