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How should I run fans for intake/exhaust?
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How should I run fans for intake/exhaust?Posted:

tucker102
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I have a phanteks p400 case. I have 5 fans total. 2 on the front, 2 at the top, and 1 in the back. It is my understanding that I want to have the back and top fans exhausting air and the front intaking. But won't this great negative pressure in my case sucking in more dust? Since I will have 3 fans exhausting and only 2 intaking?
#2. Posted:
TaigaAisaka
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Not really. Any fans as intake will suck in more dust than if all fans were exhaust, the problem arises more depending on placements of the fan(s) and the living situation around you. Example, if you had a case that allowed you to have two fans on the bottom of the case, you put them as intake and you put your PC on a wooden floor, whatever dust or pet hair that is on the floor, has a much easier time getting in the case. Another example would be having your top fans as intake. Heat rises, so the temperature above your PC case is going to be warmer than at the bottom of your case. Now in this example, since you have your exhaust pushing out the air in your PC, that would naturally rise up, but because your top fans are intake, now you are pushing that air back into the PC.

There is never a perfect solution to balance out negative and positive air pressure. Every PC has some sort of hole, vent, gap, anything to help with air flow and air exhaust. Your PC would have to be in an air tight case, using a liquid that could sustain the heat generated from the PC, without dispelling it's own heat, like liquid nitrogen but that isn't reasonable by a lot of people's means. I typically tend to go for a more positive pressure in my case, but that's because the cases I use, allow me to do so with more fans. Example, I am using the Be Quiet Dark Base Pro 900 right now. Front supports 3 140mm fans and the bottom of the case supports 1 140mm, maybeeeeee 2 120mm if your PSU is very small. It supports 1 140mm on the exhaust and 3 140mm on the top or 4 120mm on the top. What I opted for is 2 140mm in the front to cover my radiator, while using the last fan spot as my optical bay drives. 1 140mm at the bottom to blow air up where the front fans are to get a nice diagonal air flow going. Exhaust is the 140mm and the top is the 4 120mm fans, all using high flow fans, except for the front fans which are high pressure fans. My intake fan at the bottom is pushing air up, which meets with the intake in the front, this creates a diagonal air flow, but also does have coverage for vertical and horizontal airflow, covering my GPU, PSU, motherboard and the bottom of my RAM sticks. Everything other fan in exhaust is taking that now hot air and discarding it away from my PC and I get some temps I am proud with. On an old case of mine - Corsair 750D, I used to have too much positive pressure, because I would mount the radiator to the front of the case, mount 2 fans onto the front of the rad as intake, then mount 2 more fans on the back of the radiator as exhaust, in which I had a total of 7 exhaust fans and only 2 intake fans which I didn't need at all and would give a really uneven airflow for air trying to escape.

Overall, 2 fans in the front is great, if you're using a radiator or an AIO, I would suggest mounting it in the front of your case so that way it's the coldest possible air hitting it, to cool the components better. 2 exhaust fans on the top and one on the back is great for a positive pressure ratio. If your case allows a fan to be installed inside on the bottom of the case and your PC isn't on carpet or on the floor with a lot of dust/dog hair, it's absolutely reasonable to have a 3:3 ratio for positive and negative airflow. Dust is going to happen regardless, just takes a minute or two to dust your desk or your PC case every day or every other day to help keep the dust minimal. If you have carpet and pets, vacuum your room every other day. If your PC is going to be under a ceiling fan or vent AC, clean them good before putting your PC there and clean them constantly if they've been in use. Try not to keep your PC near an open window since that just lets whatever is outside to come into your room, which your PC then can just suck in.
#3. Posted:
tucker102
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Thank you very much for the detailed reply. Much appreciated.
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