Presuming you are pushing some CFM out of a case, why do you need a intake fan pushing that sam CFM in? Would not the difference in air pressure supply exactly as much fesh air as you push out?
Jeff Heidman
Jeff Heidman
Why is an intake fan even necessary?
- Thread starter Berkut
- Start date
Bignate603
Lifer
- Sep 5, 2000
- 13,897
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Air pressure would equalize but not in a controlled way. It would suck air and dust through your floppies, cd-roms, and any other nook and cranny that isn't supposed to have air go through it. At least if it's blown in you can control where it comes from and stick a filter on the fan to keep your computer clean. It's much better to have more intakes and have air flow out of these places instead of in. Read a paper on this by Cliff Anderson, creator of the Fanbus over at www.tweak.cc
the point is well made, the usage of the intake is to get cooler air into your case and to direct it where you want it... also, if you just rely on your "exhaust" fans to bring air in, the air resistance and obstacles inside your case will prevent the suction from bringing in much air... in short, depending on your fan setup, you are either causing drag on your air flow (which isn't very useful), cauing a slight pressure build (more intake, which i thik may actually help), or have even flow which just promotes a steady reliable flow of cool air over your components...
I disagree. I believe that more exhaust (a slight vaccum) is best. (Why ya think it's COLD in Space???) AMD agrees with me too. (See the PDF file here) AMDTechDocument Basicly AMD says that under "Extreme" Conditions (read Extreme as a very hot Video card) that a front Intake fan can actually contribute to CPU heating by blowing pre-heated air into the CPU's Fan/Heatsink. The BEST way to cool a case is in 3 sections. Lower: PCI/AGP Cards with a Front Intake fan or Card cooler (Exhaust)..... Mid: CPU with an Exhaust Fan right behind the CPU ..... Top: Drives with the PS Fan (Exhaust) or a Bay Cooler. Think about it.
I don't entirely agree with you, Wolfman35 or AMD. In most cases (no pun intended) the case is a tower, so the orientation of the motherboard is vertical - with the hot video card beneath the CPU. Heat rises, and the air moving up to the CPU from the video card is going to be hot. Take a video card like a Creative Labs Annihilator2 Ultra 64MB GeForce2 Ultra, with a fan/heatsink assembply on it's processor, and heatsinks on the RAM, and 64MB of RAM to boot, and you're going to be genreating a hellof alot of heat right below the CPU.
I don't think that a properly installed front fan is going to merely recirculate the hot air. I believe that, if you have enough fans pulling air out of the case, then like Bignate603 posted, you're going to have some more control over where the air comes in form, and whether you've filtered it or not.
I don't think that a properly installed front fan is going to merely recirculate the hot air. I believe that, if you have enough fans pulling air out of the case, then like Bignate603 posted, you're going to have some more control over where the air comes in form, and whether you've filtered it or not.
The design of ATX cases means that expelling fans work more efficiently than intake fans. Six inches away from my processor there is a 47cfm fan. I would rather have this fan extracting than blowing the CPU heat all over the case: can you understand this?
Argument has been made of potential dust problems through intake over drives. I don't know of any instance where this has proved a problem.
Most cases have air intake through the front bottom, and rear to the left of the cards in tower orientation. This sounds fine for the cards but all I would worry about is certain hot hard drives.
I have never seen an airflow diagram like the ones done of cars, in a computer case. I do however think that intake fans are relatively inefficient. And they are poorly placed in computer cases. Ideally it should connect flush with the front holes on the case, but almost invariably it does not, and instead pulls almost uselessly more air from inside the case.
I think that instead of blindly following rules as to how many intake fans to extractors, one should look at the airflow design of the case. I can see successful logic in overclockers cases that use intake fans in the side and top of the case.
Argument has been made of potential dust problems through intake over drives. I don't know of any instance where this has proved a problem.
Most cases have air intake through the front bottom, and rear to the left of the cards in tower orientation. This sounds fine for the cards but all I would worry about is certain hot hard drives.
I have never seen an airflow diagram like the ones done of cars, in a computer case. I do however think that intake fans are relatively inefficient. And they are poorly placed in computer cases. Ideally it should connect flush with the front holes on the case, but almost invariably it does not, and instead pulls almost uselessly more air from inside the case.
I think that instead of blindly following rules as to how many intake fans to extractors, one should look at the airflow design of the case. I can see successful logic in overclockers cases that use intake fans in the side and top of the case.
Bignate603
Lifer
- Sep 5, 2000
- 13,897
- 1
- 0
i agree that you need to look over the airflow of how air would go in and through your system. The general idea is that air flows in down near the bottom front of your case then out near the power supply. This can supplemented by extra blowholes on the side and a exhaust fan on the top. This seems to work best because the hot air rises so you just force it out the top instead of trying to suck it down to the bottom. Oh and one more thing, have you ever LOOKED inside an old drive? they're chock full of dust and crap, the collect it like crazy. Personally i don't want a drive frying on my just cause it gets clogged from crap...
A computer case fan is always working against some amount of airflow restriction- thru the grilles, around corners etc, so it always moves less air than if it were suspended out in the open. Adding an intake fan to a case with an exhaust fan helps overcome restriction, improving airflow.
The effect varies a lot from one case design to another, however. The front plastic bezel designs of most computer cases have lousy airflow characteristics, and front fans often achieve more recirculation under the bezel than actual intake. Because many cases have vent slots down low in the side panels, it is often best to put the only fan or the most powerful fan blowing out the back behind the processor. The popular Enlight 7237 is only one example like this. The front fan can't pull diddly thru the small slot under the front of the bezel, and the holes in the front are a joke. lots of air recirculates under the bezel. It does, however, have all those nice vent slots on the bottom of the side cover, so move the fan to the back and voila, better cooling.
This all changes in a case with low restriction bezel and front intake filters, of course. Then the strongest fans should be in the front, behind the filter, so that intake air is actually filtered....
The effect varies a lot from one case design to another, however. The front plastic bezel designs of most computer cases have lousy airflow characteristics, and front fans often achieve more recirculation under the bezel than actual intake. Because many cases have vent slots down low in the side panels, it is often best to put the only fan or the most powerful fan blowing out the back behind the processor. The popular Enlight 7237 is only one example like this. The front fan can't pull diddly thru the small slot under the front of the bezel, and the holes in the front are a joke. lots of air recirculates under the bezel. It does, however, have all those nice vent slots on the bottom of the side cover, so move the fan to the back and voila, better cooling.
This all changes in a case with low restriction bezel and front intake filters, of course. Then the strongest fans should be in the front, behind the filter, so that intake air is actually filtered....
Well, there isn't a set in stone answer. Every case has been looked at differently when it comes to needing more exhaust or more intake(depending on whether the case is stock, or has been modded, etc.).
My modified 7237(which is modified to help alleve the forementioned intake hole problem) works much better with the front intake fans on, rather than off.
For example, with my side 120mm and 2 front 80mm's going, the case temp is 23C and cpu temp 40.
With those intake fans off(leaving 2 92mm exhaust fans, + enermax p.s. exhausting air), case temp goes up 26, and cpu temp goes up to 43.
With only the intake fans on, my temps are 24 case, 42 cpu.
I have slightly more in-cfm's than i do exhaust-cfm's. My setup works great for me, and for me to get optimal temps, i need the intake fans going.
Pics of my case(old, but roughly the same as it is now), can be seen here My Case.
Mike
My modified 7237(which is modified to help alleve the forementioned intake hole problem) works much better with the front intake fans on, rather than off.
For example, with my side 120mm and 2 front 80mm's going, the case temp is 23C and cpu temp 40.
With those intake fans off(leaving 2 92mm exhaust fans, + enermax p.s. exhausting air), case temp goes up 26, and cpu temp goes up to 43.
With only the intake fans on, my temps are 24 case, 42 cpu.
I have slightly more in-cfm's than i do exhaust-cfm's. My setup works great for me, and for me to get optimal temps, i need the intake fans going.
Pics of my case(old, but roughly the same as it is now), can be seen here My Case.
Mike
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