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Heatsink CFM > Case fans CFM question

post #1 of 12
Thread Starter 
Just a question:

Say I have a heatsink with 2 fans in push-pull @ 95CFM each and say you have 4 intake and 4 exhaust case fans @ 40 CFM each...

What kind of impact would this have on overall airflow and cooling performance?
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post #2 of 12
As long as you have the airflow from the heatsink oriented with the rest of your case airflow, temps should be fine. I suggest having the heatsink airflow exhaust towards the top of the case.
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post #3 of 12
Thread Starter 
Thanks for your input. Any other opinions? Should I get higher CFM fans? the good think about the fans I have is that they are completley silent - like 9dba @ 900 RPM. I just see so many people with fan controllers to dial back loud fan speeds and thus CFM, so why not just get these low cfm, silent fans if the heat sink won't cause any problems?

Although this has me thinking of the Frio over the Spire Thermax Eclipse II as the stock fans have built in fan controllers to dial back the speed...
Edited by grassh0ppa - 3/4/11 at 6:36am
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post #4 of 12
Quote:
Originally Posted by grassh0ppa View Post
Thanks for your input. Any other opinions? Should I get higher CFM fans? the good think about the fans I have is that they are completley silent - like 9dba @ 900 RPM. I just see so many people with fan controllers to dial back loud fan speeds and thus CFM, so why not just get these low cfm, silent fans if the heat sink won't cause any problems?

Although this has me thinking of the Frio over the Spire Thermax Eclipse II as the stock fans have built in fan controllers to dial back the speed...
CPU heatsink fans usually have a PWN controller (4 wires), which changes the fan speed according to the CPU temp. This is a pretty handy guide: http://www.overclock.net/air-cooling...uide-fans.html
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post #5 of 12
Quote:
Originally Posted by grassh0ppa View Post
Just a question:

Say I have a heatsink with 2 fans in push-pull @ 95CFM each and say you have 4 intake and 4 exhaust case fans @ 40 CFM each...

What kind of impact would this have on overall airflow and cooling performance?
Your case fans will interfere with your cpu heatsink fans. Remove your rear grill and rear fan. Leave the opening and aim the cpu exhaust there. Fewer fans = less noise. An opening means that air leaves quietly.

Quote:
Originally Posted by Eugenester View Post
. . . I suggest having the heatsink airflow exhaust towards the top of the case.
This was established by Intel, back when the motherboard had more components that needed cooling than the cpu. These days you generally need to cool the cpu and the gpu. Bottom-to-top gets you air that is warmed by mb components before it gets to your heatsink. That kind of airflow compromises your cpu cooling.

These days, feed fresh air to your heatsink.

Quote:
Originally Posted by grassh0ppa View Post
Thanks for your input. Any other opinions? Should I get higher CFM fans? the good think about the fans I have is that they are completley silent - like 9dba @ 900 RPM. I just see so many people with fan controllers to dial back loud fan speeds and thus CFM, so why not just get these low cfm, silent fans if the heat sink won't cause any problems?

Although this has me thinking of the Frio over the Spire Thermax Eclipse II as the stock fans have built in fan controllers to dial back the speed...
You have a Gigabyte board. You don't need a fan controller. You can control any fan with your mb. You can control PWM fans with PWM. With a change in your BIOS settings you can control even non-PWM fans by varying their voltage.

Quote:
Originally Posted by Eugenester View Post
CPU heatsink fans usually have a PWN controller (4 wires), which changes the fan speed according to the CPU temp. This is a pretty handy guide: http://www.overclock.net/air-cooling...uide-fans.html
That's true for the As.s you and I have. OP is not limited in this way.
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post #6 of 12
Thread Starter 
Ok, thanks for the input guys I really appreciate it. A couple more questions have arisen:

I don't see how removing the rear fan and grill would help... The air is being pushed toward the back already, and with and with no rear fan or grill it would just pass through normally... but if I left it as is wouldn't the rear fan help guide air thats going to be travelling through anyway? or would it reflect a lot of the air and bounce it around the case?

Perhaps I'll do some experiments when I get the components.
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post #7 of 12
Rule of thumb with fans: use as many as you can, as powerful as you can without costing too much or being intolerably loud. More air the better.

But yeah, lower CFM case fans and higher CFM heatsink fans is a good setup. The problem with lower CFM case fans is the air from them won't be directly hitting vital components and affecting temperatures drastically.
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post #8 of 12
Thread Starter 
Do you think 40CFM is too low for case fans?

i remember reading someone talking about how high CFM fans may not be the best choice because it takes time for the cooled air to be heated by components, and if you have high CFM fans then the heat transfer wont be as great. So there is a point where more CFM isn't necessarily better?
Edited by grassh0ppa - 3/4/11 at 6:52pm
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post #9 of 12
In my case I have several fans pushing air into the case and none pulling air out. I use lowspeed quiet intake fans. An exhaust fans would add nothing but noise.

If I had higher powered case fans, the exhaust fan would just impede air getting out of the case - it couldn't keep up.

An exhaust fan often cannot keep up with a heatsink's pull fan. Just gets in the way.

In any case, you don't need and exhaust fan. See item 2 in my sig.

Edit: 40cfm is not too low. Both of my 120mm intake fans are less than that.
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post #10 of 12
Thread Starter 
Interesting!! I think I may try the no exhaust fans and just go with 4 intake fans. The fans im using come with the arc midi, and ill buy 1 extra maybe... http://www.fractal-design.com/?view=...gory=4&prod=19 I love how quiet they are. My last rig was loud and the noise bothered me.

Would your method still work reasonably well without the fan grills removed?
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