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Jester
(@jester)
Member Moderator

In order to properly cool your PC and its components, a good airflow setup is a necessity. Most pre-built PCs come with lousy airflow, thus heating up your components rather quickly. The use of fans is very important, and so is the location and orientation of the fans.

This thread is for ATX cases only.

Here is a proper airflow setup.

  • Front: Intakes
  • Bottom: Intakes
  • Side: Intakes (usually, read below for more)
  • Top: Exhausts
  • Rear: Exhausts

In some situations, you might need the side fan(s) to exhaust air out of the case. You only want to do this if you are using certain video cards that exhaust heat to the side, such as the 9800GX2 or GTX 295. This is less of an issue with the GTX 295 since the fins on the side of it are pointed to the rear of the chassis.

Here is an example of the fans put to use the way they should be.

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As you can see, the front fan takes in air since it is low. Cool air is heavier so it stays lower, hot air is lighter therefore it rises. If you have a case like the Antec 1200 where the front fans reach up near the top of the case, they should still be intakes, so you can have positive air pressure.

As I said, cool air is heavier so it remains lower. This is why you want your bottom fan(s) to intake air from outside the case and blow it all around the case.

Once again, hot air rises, therefore top fans should automatically be exhaust fans. Same goes for the rear, since they are positioned right next to the CPU which is pretty high up (except for BTX configutations). Plus, most after market heat sinks direct heat to the rear fan, and take cool air from the opposite side.

Lets get more advanced. If you use some internal fans such as the two in the hard drive cage of the CM ATCS 840 case, or a similar configuration, they should blow air around the case as well. External air ducts should exhaust heat, since dual slot video cards exhaust heat out of the case.

You also want your PSU fan (if it has one on the top of it) to face open ventilation. This is because PSU fans blow air over the PSU components, and the air is then exhausted out of the case. Lots of cases don't have proper ventilation for the power supply. But if your PSU is on the top of a case, it should face down in order to exhaust air, acting as a top exhaust fan.

If the top fans are too close to the front of your case, then you don't want them exhausting air. They would draw out air prematurely before it gets to cool your CPU and video cards. You wouldn't want them intaking air either - this can disrupt the airflow in your case and increase dust. Therefore it is best to not use any fans in such spaces.

What About Air Pressure?

The air pressure of a case matters as well. You can have positive air pressure, neutral air pressure, or negative air pressure.

Negative Air Pressure

Negative air pressure is probably the most common. It should really be avoided. In order to have negative air pressure, you must have more exhaust power than intake power. As a result, air is passively drawn in through open slots and ventilation. This would bring in more dust, and make it harder for video cards to exhaust air since the flow of air is going against it.

Positive Air Pressure

Positive air pressure is not as common in computer cases, but it is the preferred method of cooling. In a positive air pressure system, you must have more intake power than exhaust power. As a result, air passively leaves the case through open slots and ventilation. This reduces the amount of dust in the case, and it makes it easier for video cards to exhaust air since the flow of air is going with it.

Neutral Air Pressure

Neutral air pressure means you have equal intake power and exhaust power. This is a better method than negative air pressure. In a neutral air pressure system, there is less air passively moving into and out of the case. Overall I still prefer positive air pressure, because video cards can exhaust air easier which is vital for Fermi owners such as myself.

Advanced Configurations

With multi-GPU setups, especially NVIDIA's GTX 400 series, you may have to get creative with the airflow in your case. One of the cheapest yet most effective options is channeling air to your video cards. This can be done with simple plastic air ducts. Take a look at the Cooler Master HAF-X case for good examples of this.

To make these effective air ducts, all that is needed is some plastic and cutting tools. The HAF-X has a duct on the side 200mm intake fan to route air over the video cards. This can be done with any size fan.
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The object on the right shows another air duct included in the HAF-X. This is mounted on the back of the HDD cage and can accept a 120mm x 25mm fan or 120mm x 38mm fan. There is even space to route the fan cable.
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Here is an image of this air duct with a 120mm x 25mm fan mounted.
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Below you can see the air duct installed. Notice how it can channel air to three video cards, despite the fact that the HAF-X supports four video cards. So compensate for future upgrades. Create what you may need.
3305_35_full.jpg

Here is a close-up of the GPU air duct and a GPU support bracket which is included with the HAF-X. This bracket can hold an 80mm fan, and helps secure video cards. Not necessary, but no harm done.
cooler_master_haf_x_038.jpg

Here is everything installed. The VGA air duct and VGA support bracket which is covered by the side air duct. The air duct had to be rotated 180 degrees to fit the support bracket.
cooler_master_haf_x_042.jpg

So now you know how to cool a case. But what do you cool it with? Here is my list of recommended fans but first you should know about the types of bearings used.

  • Sleeve bearing fans use two surfaces lubricated with oil or grease as a friction contact. Sleeve bearings are less durable as the contact surfaces can become rough and/or the lubricant dry up, eventually leading to failure. Sleeve bearings may be more likely to fail at higher temperatures, and may perform poorly when mounted in any orientation other than vertical. The lifespan of a sleeve bearing fan may be around 40,000 hours at 40 °C. Fans that use sleeve bearings are generally cheaper than fans that use ball bearings, and are quieter at lower speeds early in their life, but can grow considerably noisier as they age.
  • Rifle bearing fans are similar to sleeve bearing, but are quieter and have almost as much lifespan as ball bearings. The bearing has a spiral groove in it that pumps fluid from a reservoir. This allows them to be safely mounted horizontally (unlike sleeve bearings), since the fluid being pumped lubricates the top of the shaft. The pumping also ensures sufficient lubricant on the shaft, reducing noise, and increasing lifespan.
  • Ball bearing fans use ball bearings. Though generally more expensive, ball bearing fans do not suffer the same orientation limitations as sleeve bearing fans, are more durable especially at higher temperatures, and quieter than sleeve bearing fans at higher rotation speeds. The lifespan of a ball bearing fan may be around 63,000 hours at 40 °C. Some fans use one ball bearing, some use two and some use one ball and one sleeve. The latter is cheaper and less effective.
  • Fluid dynamic bearing fans have the advantages of near-silent operation and higher life expectancy than even ball bearing fans, due to the lack of contact with the shaft, bearing and thrust plate. However, these fans tend to be the most expensive.
  • Magnetic bearing fans, in which the fan is repelled from the bearing by magnetism. Stabilizes the rotor axis. Noctua's Self-Stabilizing Oil Pressure Bearing (SSO Bearing) is a fluid dynamic bearing with a magnet.

Recommended Fans

Noctua NF-P14 - Very high end 140mm x 25mm fan. Limited compatibility, uses SSO bearings. Performs up to 1200 RPM/64.96 CFM/19.6 DBA. LINK

Scythe S-Flex - There is a large variety of Scythe S-Flex fans. The differences are the rotation speed, therefore the CFM and noise values are different as well. These 120mm x 25mm fans use a fluid dynamic bearing and are very high end. LINK

Scythe GentleTyphoon - There are a few GentleTyphoon 120mm x 25mm fans. The differences are the rotation speed, therefore the CFM and noise values are different as well. These fans use ball bearings and offer very good static pressure, better than all of the other 120mm x 25mm fans in this category in the same RPM range. They also run rather quiet considering their speeds. LINK

Thermalright FDB - There are four Thermalright FDB fans. The differences are the rotation speed, therefore the CFM and noise values are different as well. These 120mm x 25mm fans are identical to the Scythe S-Flex fans, however the rotation speeds are a bit different. LINK

High Airflow Fans

  • Delta - Delta has a large variety of 120mm x 38mm fans, all of which are very high quality (ball bearings), and feature unrivaled airflow. The obvious downside is noise level considering the speeds at which they spin. LINK
  • Panaflo - Panaflo has good 120mm x 38mm fans that aren't incredibly noisy and have a very good construction. They use hydro wave bearings which are very quiet and the lifespan is very long. LINK
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Posted : 01/05/2009 8:54 pm
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