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AF vs SP fan for Rear Exhaust?


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AF, Sp is designed to push air through a radiator and is optimised for Static Pressure. AF fans are high Air Flow which is what yo need.

 

Agreed. What I'm asking though is if the honey comb mesh qualifies as enough resistance. I think I saw a Linus Tech Tip where he was saying Corsair suggests using a SP fan if there's less than 3cm of clearance. The honey comb mesh is definitely less than 3cm away from the fan. Does the mesh warrant using an SP fan?

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The 3cm is a little more important on the intake side of the fan, although the side of the fan where the resistance is located does not matter from an physics standpoint. The design of the AF series is going to pull air from a wide area. Completely restricting one side or the other (dense radiator, full stack HDD) would substantially restrict its airflow. The SP would also be heavily restricted by that resistance, but its blade design is better and pulling from a more central area and might offer better direct cooling. So if you are looking to remove the most air from the rear of the case, the AF is the one. If you have something specific you are trying to cool on the front side of that fan, then it might bear closer scrutiny.

 

If this is for the CM Cosmos 1000, that honeycomb on the rear isn't enough to qualify as heavy resistance. You are most likely going to be happier with an AF120. Generally with 120mm fans, you really need to have substantial resistance before the fat and flat blade fans win out. Most 120mm fan are hybrid blade designs anyway, so it doesn't matter. The AF120 is not, but that would still be my recommendation.

 

With 140mm fans there is a little more wiggle room. 140's in general have a wide spray pattern and the "static pressure" models in that size are often a little more open than a comparative 120mm model. I just took a SP140-like fan off my rear exhaust today. A few months ago I was quite surprised to see it did a better job evacuating air from the rear of the case than one of my AF140's, which has a definite airflow advantage. It has nothing to do with resistance, but the specific layout of my case and hardware made the more pressure orientated fan ideal for pulling air across the rear heat sinks. This is the exception to the rule.

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Thanks c-attack for that response. Although I'm quite confused by it. You seem to suggest an AF fan for the exhaust but then state that you like a SP fan better for that job.

 

Let's make this super simple...

If I were to cut the honey comb out of the exhaust port, I'm pretty sure an AF would be perfect.

But if I were to leave the honey comb in, does that resistance, less than 3 cm away from the fan warrant a SP fan?

 

My case is a Cosmos II and I'm talking only about 140mm fans.

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Get the AF140. Don't cut the mesh.

 

Sorry, I'll clarify. Any kind of rear grill is not going to be so restrictive that an airflow fan will move less air than a pressure designed blade. The AF fan is better. You need a radiator, a full stack of HDDs, or a very fine filter before this changes. With 120mm fans, it is easier to be definitive in this statement.

 

I am too tedious about fans to leave it as a blanket statement of fact and I made that example to illustrate there are no universal rules. My pressure orientated fan is doing a better job, not because of any resistance (my rear grill is removed), but because the motherboard heat sinks and left side X99 memory are benefiting from that fan being directly in-line. I have great airflow in my Air 540 and I don't need maximal rear exhaust in my system. That rear air stream is often cool, even when gaming with 970 SLI. The AF140 moves more air out of the case, but it pulls from a wider area outside of the heat sink which is the only meaningful metric I have to measure it. If you have an X99 and your VRM is 3C cooler, you notice.

 

When you move into the 140mm models, the pressure variant is a little more like an airflow fan - more space between blades, steeper rake. You are giving up less airflow on when choosing a more pressure orientated fans, but also getting less focused pressure in return. There are no 140mm fans that look like a big SP120 and you probably wouldn't want one.

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