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case fans blow forward ???

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June 24, 2008 1:54:26 AM


Hi,

I am about to build a system to fit my needs. My question is WHY DO ALL CASES VENT OUT THE BACK?.
In the location I plan to place the tower, desk against a wall tower by desk, it is actually cooler near the wall, not in the middle of the room. So if I vent all exhaust out the front, it will pull cooler air in from the rear. Of course the PSU will still vent out the rear. I know, I know, if I do this I will have hot air basting into the room. But perhaps better than hot air blasting out the back circulating near my feet ( I don't like hot feet). Also the hot air directly into the room would get picked up by the hot air return for the AC.
Would love comments about this.

More about : case fans blow forward

June 24, 2008 2:59:22 AM

Easier, free-er access to air?

No hot air blowing on the user?

Location of drivers versus MB?




Take the drives versus MB issue.

You want access to your floppy and optical drives, hence the drives are on the front the case. The MB takes up a big chunk of space and the drives take up a fair amout of space.

IF you were to mount the drives at the front, where do you mount the MB? The logical answer is at the rear of the case.

The drives need cooling, not a lot of cooling, but some neverless. IF you pumped air from back to front, the drives would be receiving the HOT air from the MB with only minor temperature differentials between the hot MB air and the temperatures of the drives, or in some cases the hot MB air would be warmer than the drive temperatures. Whereas in the exisiting drives to the front, MB to the back, the drives are cooled and the air from the drives flowing to the MB is only slightly warmer than ambient temperature air entering the computer.



Hot air blowing on the user?

My tower unit is mounted on my desktop, 'cause I have a corner desk unit and that is the only way the standard cables would reach my monitor. IF the air flow was back to front I would get a blast of warm air into my left ear. Not good. Guess what? Most people have similar setups, or at least the tower unit is near their monitor, often facing the user for ease of access to the drives.

Them darn drives again.



Easier, free-er access to air?

Yep. Many people use air filters on their towers. Ok, maybe not many, but there are a good number that do use air filters. The air filters must be cleaned once in a blue moon for good operation. Having the filter at the back would not encourge regular cleaning of the air filter.


Another reason is diffusion of the hot air.

Air that hits a flat wall is forced to travel in different directions (diffusion). The quicker the hot air is diffused, the less noticeable the hot air will be to persons in the room. This is especially true if the hot air was blowing from the front of the tower into the room.


There is no reason (other than those darn drives) why you have to mount your exhust fans to the rear.

Ooops, like you said, there is that pesky PSU pumping out hot air (and circulating right back into the machine through the MB fan).

But hey, just flip the PSU and MB around with their respective fans and then find another spot for your drives and you can have a machine blowing hot air into your room rather than the wall.
a b B Homebuilt system
June 24, 2008 3:07:07 AM

For a starter, Hottest air is at ceiling, coldest is at floor.

Your rear fan is center rearof case inline with CPU. Air intake is generally bottom front of case (Most cases also have a intake fan located front botttem (Generally more restrictive - less air flow) Inside of case Hot air rises.

So, Two things - 1) to reverse this flow would be counter perductive as it would be fighting the natural air currents. 2) By having the intake at the rear a part of this air would be siphend off (suck off) by the PSU fan thus reducing the air flow accrose the CPU.

Bottom line best to have rear fan blowing out, front fan blowing in for best CPU cooling.
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June 24, 2008 3:26:30 AM

Sure. Whatever you want to do. It's just fans, do em like you want.

We could discuss what direction to twist a pencil when sharpening it on a piece of sandpaper too.
a c 84 B Homebuilt system
June 24, 2008 4:09:25 AM

RetiredChief has it right.

In addition, the hot psu air would get pulled back into the case. That is why you don't see the heat/ac return duct next to the supply duct.

Also, some vga cards are a two slot type that sends the hot air out the back of the case.

Some cases have intakes on the bottom, and exhaust on the top.

June 24, 2008 4:27:46 AM

Thanks,
I knew this would stir some "hot air", but I was really curious. I guess compliance with standard design is really best. Thanks for the drives/motherboard issue, and I'll be sure to have intake low in the front, and I guess exhaust high in the rear. As far as house/office AC outlets and returns, has anyone thought about office design where some of the AC ducts are split to feed directly into the tower intakes....could be an interesting design/layout if one gave it some thought. Thanks again.
a b B Homebuilt system
June 24, 2008 3:48:35 PM

The front of my case is 4 ft from the A/C vent with a Directional cover angled toward the case. I have a temp sensor located about 2 in from the HSF. A/C off = inside case temp 80 F when A/C clicks on Case temp drops to 72. House termostat set to 77 F. This also equates to about 6 C delta on CPU core temps.
June 21, 2009 7:33:38 PM

Some way some how get a gap between (4 inches or more) the wall and case use an outside household fan to help out if needed . Everything else you mention is bunk. I once had a bunch of case fans that added more heat than they took out .I once bought a 250 mm fan that blew dust into my case, I didnt know it blew that way till I had cut a big hole in my side panel .I eventually closed off the hole just enough to add a 120 mm with a filter since they don't make filters for 250 mm's All I'm saying is experience is the best teacher and sometimes less is more.The front to back airflow is as about as good as it gets.
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