Front and Rear fans

[ManBearPig]

It seems split 50/50 that people think front should be intake and rear exhaust. anyone wanna shed some light on this?

 

[pcy]

Hi,


I have never hward anybody suggest aby way other than Front Intak and Rear Exhaust.


Clearly, you want airflow through the case, so you have to have one inake and one exhaust.

But the rear must be exhaust, because it is near the CPU. It's absolutely essential that as much of the hottest air (i.e the air that has been used to cool the CPU) should be expelled out of the case. Otherwise it recirculates, and simply serves to heat up the entire inside of the case including, of course, the air used to cool the CPU.


Taht's it.




Peter

 

[VinDSL]

Sorry for being ambiguous, but whatever works for you is best...

That's probably why opinions are split on this topic!

I have a friend that builds computers (small business -- 5 employees) and he swears top exhaust is best... 😀

 

[ManBearPig]

i tried to tell by manually spinning the fan but is there any actual indication on the fans which direction is exhaust and which is intake?

 

[Zepper]

You mount the fans to blow in the direction you want. If you look carefully on the frame of most fans you will find two little arrows. One points in the direction of air flow for that fan and the other points in the direction of blade rotation. So for intake you want the air flow arrow pointing into the case, and for exhaust you want the air flow arrow pointing out of the case. Simple isn't it?

Most standard fans can be used for either intake or exhaust mounting but there are some unusual fans like some Arctic Cooling and some Silverstone units are difficult to use for intake fans on some cases. But some cases like the Rosewill/YeongYang 560x series can use such fans as intake due to the way they implemented the intake fan area. Or you could improvise a mounting to use them as intake in any case.

Generally a lower front mounting is appropriate for intake and an upper rear for exhaust since warm air naturally rises. Most find that top blow-holes don't add much to overall cooling - and provide an entry point for accidentally spilled beverages, etc. - just say no! If there is one present, block it off with something.

..bh.

 

[LOUISSSSS]

Originally posted by: VinDSL
Sorry for being ambiguous, but whatever works for you is best...

That's probably why opinions are split on this topic!

I have a friend that builds computers (small business -- 5 employees) and he swears top exhaust is best... 😀

any fan on the top of a case should be exhaust, unless under special circumstances... heat rises, it would be counter-productive if you were to have the heat rise to the fan only to push it back down to your parts

i'm planning to switch my fans to front intake, rear intake, lian li v1000 blower exhaust, top 120mm exhaust, any opinions?

 

[pcy]

Hi Guys,


The warm air rising thing is utterly irrelevant if you are using a case with ventiltion fans


The effect exists, but it's insignificant - swamped by othe considerations.


What matters is:
1. There must be aiflow through the case, so that all componenets recieve some cooling, and so that the inside of the case as a whole, and the air input to the CPU cooler in particular, remain cool
2. The CPU must be situated near an exhaust fan, so that the hot air coming off the CPU cooler exists from the case rather than re-circulating.


The conventional arrangement - intake at the bottom front and outlet through the top back meets both these criterion. In a particular case other layouts may also work well; but if the PSU is in the conventional place - i.e. above the CPU, at the back - a top exhaust fan could actually makes things worse, not better. If you have a top exhaust fan as well as a back one that's fine; but if you have only a top exhaust fan and the PSU is between the CPU and the exhaust fan, the hot CPU exhaust air will be heating up the whole machine.



Peter




Peter

 

[Zepper]

"Warm air rising irrelevant..." Well, if that is the case, why not put the exhaust fan straight across from the intake fan at the bottom of the case? I'd bet you'd get at least a 5 deg C rise in case temps. But it would be hard to test as no case maker that I know of does it that way for some strange reason... :roll:

.bh.

 

[pcy]

Originally posted by: Zepper
"Warm air rising irrelevant..." Well, if that is the case, why not put the exhaust fan straight across from the intake fan at the bottom of the case?

Because if you did that the exhaust fan would no longer be close to the CPU. If you read my post it says..

2. The CPU must be situated near an exhaust fan, so that the hot air coming off the CPU cooler exists from the case rather than re-circulating.

The conventional ATX case (bottom front in, top back out) withe the CPU close to the exhaust fan) was designed that way for a reason. Specifically, the air path traverses the case and the CPU is close to the exhaust fan.

I'd bet you'd get at least a 5 deg C rise in case temps. But it would be hard to test as no case maker that I know of does it that way for some strange reason... :roll:

Not strange at all... if you did that most of the case would recive no airflow but th bottom would be nice and cool.



After all, the same case layout works fine in desktop or rackmount mode without any help from gravity.



Peter

 

[yiranhu]

Heat rising in general is irrelevant. Your fan moves the warm air out before it has the chance to rise. Think of fire place... it takes very long for you to feel the heat generated by that fire. If you build a fire outdoors with wind, you have to put your hand very close to the fire to even feel the heat.

The only reason why the rear exhaust is on the top is because the CPU and PS and other heat generating machinery are on the top. It would actually be better if the front intake fans are on the top. Then you have a straight line of air movement from front over the CPU and out the back. Unfortunately the top is usually inhabited by DVD/HD and so on. So we compromise by putting a fan on the bottom.

 

[LOUISSSSS]

Originally posted by: yiranhu
Heat rising in general is irrelevant. Your fan moves the warm air out before it has the chance to rise. Think of fire place... it takes very long for you to feel the heat generated by that fire. If you build a fire outdoors with wind, you have to put your hand very close to the fire to even feel the heat.

The only reason why the rear exhaust is on the top is because the CPU and PS and other heat generating machinery are on the top. It would actually be better if the front intake fans are on the top. Then you have a straight line of air movement from front over the CPU and out the back. Unfortunately the top is usually inhabited by DVD/HD and so on. So we compromise by putting a fan on the bottom.

the front intake on the top of a pc case wouldn't be sucha good idea because all the parts below it (usually HDD's, video card, northbridge etc) wouldn't get any airflow at all
and psu's usually have their own exhaust fans

 

[Jhhnn]

With computer fans, the air is almost always exhausted towards the struts that support the center hub... The only exception I've ever seen is a special purpose papst fan horizontally mounted in industrial computers where I work...

If the case has good air intake openings in the front and/or down low on the side(s), then a single rear exhaust in the usual position is most often entirely adequate. Adding a front intake fan won't hurt, but it will often have negligible effect, other than creating more noise... Cases that don't breathe well generally benefit more from multiple fans than those that are well designed...

Pressure differentials are insignificant with muffin type fans, so don't get caught in that non-sequiter... it's all about flow...