PC fan configuration questions

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Striker051

Striker051

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May 3, 2017
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Hello guys

I have recently built an gamig pc. But i can’t get fully done airflow and fan configuration. I think my config is way to unbalanced. By my calculation my computer has 184CFM as intake and 95CFM as exhaust. So i have 3 quesions:
1. How difference should i have between intake and exhaust? I’ve heard it 30CFM difference between intake and exhaust is the best. Is that true?
2. Should i add 1 more fan as exhaust to reduce their CFM difference?
3. How much CFM does dust filters such as silvertek cut(i’m planning to add filters to all my intake fans)?

Thank you all for taking your time and helping me.

Sincerely
 
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P
I agree fully with prior posts. Doing it by the numbers cannot give you an answer, and the effect on airflow rate from adding intake filters cannot be predicted precisely. Achieving near-balance with slight excess of intake is best, but it's REALLY hard to specify an "ideal" amount of "slight excess", and impossible to quantify that with numbers.

I('ll suggest another way to approach, and I suggest you try this before adding a further fan, because you may find that fan unnecessary. Do this WITH the new intake dust filters in place so they are having their effect. With the system running (and you might do this under a few different workload and fan speed situations), do this test of air flow balance. Get a small source of smoke as a...
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Eximo

Eximo

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May 27, 2010
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Not sure anyone is going to be able to answer scientifically with numbers, way too many details missing, and I doubt anyone has enough knowledge regardless. Would almost have to get a complete part listing, build digital versions, and put it all into a fluid simulation program. Or have the actual hardware and do long term testing.

If you are going for positive pressure then extra intake is good. This will prevent dust from coming in places that aren't intended to be intakes. And filtering those intakes will catch the dust that would have normally gone in.

I've not tried a neutral arrangment, I usually go for filtered intakes. Cleaning the filters somewhat often and a regular dusting on the inside is adequate.

On my build I have filtered 280mm push/pull intake, top 280mm pull exhaust, and a filtered rear 140mm intake. That seems to do pretty well.
 
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JoeMomma

JoeMomma

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Nov 17, 2010
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Don't worry about exact specifications too much.
I'm an engineer and I know when it's time to be precise and when it's Okay to "just wing it."

1. As long as you have a little more intake than exhaust, you will achieve positive air pressure.
Fan size is more relevant than CFM specs because you should never run your fans at full CFM because that is too loud.

2. You do not mention your current config. The rule of thumb is 2 fans in, 1 fan out. 3 fans in, 2 fans out.
I have 3x 140mm fans in, 3x 120mm fans out.

3. There is no way to know how much a filter will affect CFM.
There are so many random variables that I don't think anyone bothered to test it.
Add good filters, keep them cleaned often and you shouldn't have a problem.

Configuring your fan curves is the hard part. Especially with multiple fans.
Which fan is doing the most cooling?
Which fan is making the most noise?
Do I want maximum cooling and low temps?
Or am I willing to live with higher temps and slower fans so my PC will be quiet?

I have my be quiet! fans tuned to nearly full speed, because they are Silent Wings, and my other fans are pretty slow because they make more noise.
 
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Striker051

Striker051

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My current config is i have
x2 120mm fan(69.69 CFM each) in front as intake
x1 120mm fan(45 CFM) in bottom as intake
x1 140mm fan(50 CFM) in top as exhaust
x1 120mm fan(45 CFM) in back as exhaust
So there is total 184 CFM as intake and 95 CFM as exhaust. I am thinking of adding 1 more 140mm fan(50 CFM) in top as exhaust and add filters on all my intake fans. How efficient would it be?
 
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Paperdoc

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Oct 19, 2006
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I agree fully with prior posts. Doing it by the numbers cannot give you an answer, and the effect on airflow rate from adding intake filters cannot be predicted precisely. Achieving near-balance with slight excess of intake is best, but it's REALLY hard to specify an "ideal" amount of "slight excess", and impossible to quantify that with numbers.

I('ll suggest another way to approach, and I suggest you try this before adding a further fan, because you may find that fan unnecessary. Do this WITH the new intake dust filters in place so they are having their effect. With the system running (and you might do this under a few different workload and fan speed situations), do this test of air flow balance. Get a small source of smoke as a "tracer" of air currents. I've used an incense stick. Move the smoke source close to any cracks in the exterior of the case, like near front panels and drive slots. Watch how the smoke flows. If it flows into the case, you have negative pressure inside. If it flows away from the case, you have positive pressure (likely to be your situation). ROUGHLY you can gauge the amount of excess positive pressure by how fast the smoke blows away from your case. You might even try temporarily disconnecting one or another fan to see what effect that has on the smoke pattern. For example, if disconnecting one of the 70 CFM fans at the front causes smoke flow to reverse, but reconnecting that and disconnecting the 45 CFM bottom one leaves you with smoke blowing away from your case, then you already have a good combination.
 
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