How much cfm is enough?

GamingGod · Post by **GamingGod** » Sun Feb 23, 2003 2:10 pm

Is there a formula or a rough estament on how much cfm you need through the case. My system is a 2.4ghz p4 with a 9500pro and a seasonic 300w power supply. I will be heavily gaming, and i wanted my comptuer to be as quiet as possible but i dont know how much airflow i really need.

Gandalf · Post by **Gandalf** » Mon Feb 24, 2003 1:10 am

Oooh, such a formula would be really handy!
IMHO the Intake == Outtake does the trick just fine

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tm · Post by tm » Mon Feb 24, 2003 2:22 am

It seems a rough formula for just how much CFM you need would be:

CFM = (volume of case) * (total heat dissipated by components per minute) / (heat capacity of air at constant volume)

Although I've seen this formula:

CFM = (total heat dissipated by components per minute) / ((specific heat of air) * (density of air) * (temperature out - temperature in))

(note watts = joules per second)

Which doesn't factor in the volume of the case at all. If you want a more precise formula, you'll need to find a physicist or physics student. If you want a useful formula, find someone who works on HVAC

I would think it's probably more productive to have thermally controlled fans that handle the on-demand changes in temperature (since we're mostly concerned about not hitting dangerously high temperatures for certain components), or strategies to move heat away from those components (heatpipes, watercooling).

ChiefWeasel · Post by **ChiefWeasel** » Mon Feb 24, 2003 4:24 am

Far too difficult to say i think - even if you did get a number you would need to take into account the fact that you dont know how much CFM you will get from a fan setup after it has to contend with all the obstacles in a case.

Having said that i think i would try using 2 L1a's - 1 in, 1 out, and see how low you can drop the voltages and keep decent temps.

Post by **Ralf Hutter** » Mon Feb 24, 2003 5:34 am

It's kind of like Abe Lincoln said when someone asked him how long a man's legs should be. He replyed "just long enough to reach the ground".

You need enough cfm to keep the case cool enough for you. Some of the hardcore OCers are running so many fans in their cases it sounds like a 747 taking off, just so they can squeeze the last degree of cooling into their cases. Us quiet guys cut back on the fans to get an acceptable balance of cooling vs. noise. Somewhere in there is where you need to be but it's a subjective thing: enough cooling for you may not be enough for the next guy.

GamingGod · Post by **GamingGod** » Mon Feb 24, 2003 1:52 pm

You think 1 L1A and the power supply is enough to remove all the hot air? Ill have a 120mm intake, and I could easily cut the back fan out and fit a 120mm fan in.

ChiefWeasel · Post by **ChiefWeasel** » Tue Feb 25, 2003 4:53 am

Do you have an 80mm fan you can try it with? Doesnt have to be a panaflo, jus something with similar CFM, so that you can test what temps you get...

If its too hot then maybe try using a 120mm L1a as you suggested.

Post by **Ralf Hutter** » Tue Feb 25, 2003 5:41 am

My main system (see sig) is similar to yours and my case cooling consists of (in an Antec SX1040 case) two Panaflo L1As at 7 volts on the back wall and a 18cfm NMB at 12v on the front wall, plus the TruePower PSU fans. This setup keeps the case waaay cool, even during the most hardcore gaming sessions. Case temp is 35-37°C MAX. I live in SoCal with no AC. It gets pretty toasty in here sometimes.

What's your case? Does it have good airflow?

GamingGod · Post by **GamingGod** » Tue Feb 25, 2003 10:06 am

Ive got a few different cases, but the one ill be using is the dbox. I was thinking of cutting the back hole out and putting in a 120mm fan, that way I could put in panaflo 120mmL1A in it, and maybe even turn it down to 7v or 5v with the speed control built into the case. I will also have a front 120mm fan, but since im making a cdbay sized housing for my hardrive so it can be sidesinked and then suspended, im going to put the 120mm fan on the top of the harddrive enclosure sucking air across it via bottom intake holes, and blowing it up at an angle towards the cpu/psu/video card region. Also do you think that having air sucked across an object like i have described will be noisy? I thought the it would be okay, because it will be a fairly slow moving fan and there should be a good inch all around the harddrive, maybe even 3-4 inbetween the top of the hard drive, and top of the enclosure where the fan will be.

Gandalf · Post by **Gandalf** » Tue Feb 25, 2003 10:19 am

None of the 120mm fans (all PAPST) I have are noisy at 7v or 5v, so it probably shouldn't be too much of a problem

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