Question For the 3 top fans, can I have 2 of them as outtake and 1 of them as intake?

Jan 3, 2021
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Hi guys,

I can put 3 fans at the top of my case. I will call them: rear, mid, and front fans. I currently have the rear and mid installed as outtake fans.

I am planning to install the front fan, which is the fan that is closest to the front of the case. This fan has no heat generating components below it. It is also right next to the front intake fan. As such, if I set this fan as an outtake fan, wouldn't that fan be sucking the fresh air from the front intake fan, and immediately push it out of the case?

As such, I am planning to have this top fan as an intake fan instead. However, people tend to not use top fan as intake fan. So I was wondering whether this is okay to do?

Further, the remaining 2 top fans are outtake fan. In other words, I have three fans in a row. Two of which are blowing air out while one of which is blowing air in. Would this be a problem? For example, would the intake and outtake fan interfere with each other since they are blowing air towards two different directions?

Thanks a lot.

P.S. here's a video of my build. It might be easier for me to explain with the visual:
View: https://www.youtube.com/watch?v=9BicmCzJ0xg
 

iPeekYou

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Jul 7, 2014
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Hi guys,

I can put 3 fans at the top of my case. I will call them: rear, mid, and front fans. I currently have the rear and mid installed as outtake fans.

I am planning to install the front fan, which is the fan that is closest to the front of the case. This fan has no heat generating components below it. It is also right next to the front intake fan. As such, if I set this fan as an outtake fan, wouldn't that fan be sucking the fresh air from the front intake fan, and immediately push it out of the case?

As such, I am planning to have this top fan as an intake fan instead. However, people tend to not use top fan as intake fan. So I was wondering whether this is okay to do?
Yep, you're right in assuming that the top front fan as exhaust will just suck out air from the front fan. I generally leave that particular spot open since it's another fan to connect to, and doing absolutely nothing good in the vast majority of setup.



Further, the remaining 2 top fans are outtake fan. In other words, I have three fans in a row. Two of which are blowing air out while one of which is blowing air in. Would this be a problem? For example, would the intake and outtake fan interfere with each other since they are blowing air towards two different directions?

Thanks a lot.
In theory, it would. Fans affect the airflow of devices near to them the most, naturally, and placing fans in series (side-by-side) with opposing directions is generally avoided since the intake from one fan is largely sucked out the other fan. You can make it work by, say, putting exhaust fan towards the rear, and intake towards the front.

However, then you'll have a pair of intake fans in the front that will fight each other in airflow direction. The top blows downwards, while the front wants to blow rearwards. Poor airflow in general. Again, this is why I leave the front spot open since after testing it for myself, there's zero benefit and even some loss fitting a fan over there.

In practice, it's always a toss-up. Airflow in PC case is difficult to really analyse short of empirical testing, or CFD simulation. Personally, I expect either no gains at all or even a slight loss.

A very good article on airflow. I've linked the summary page, and one of the points was about top fan near the front of the case.

3. If you have a roof mount that’s located nearer the front of the case than the CPU cooler, leave it open. Fitting a fan here only causes problems.
 
You can try it but my first thought is it will likely make the ‘mid’ fan exhaust air that the front fan has just dropped in. If the airflow between front and mid becomes at half loop then the mid fan is less effective at removing hot air from the case as it is mainly expelling cool air taken in by ‘front’ fan.
 
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dorsai

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The fan setup you have running right now is ideal with 3 in and 3 out. There's no reason to change anything.

You "might" be able to drop a degree or two off your GPU temps by moving the rad to the top of the case with the fans blowing out and moving the two fans from the top to the front as intake fans but I wouldn't bother...your setup looks pretty slick as it is.
 
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