If positive pressure is generally better...

if positive pressure is generally better, ie more intake air than exhaust, then y do the big oems usually use negative pressure. Usually its only one exhaust fan. im sure the big companies spend lots of resources making sure their pc's are going to last awhile, because no one wants thousands of angry callers saying their computer broke. so if positive pressure is better, why do the big guys use negative?

i'd say because those computers dont have that much airflow anyway. by the time enough dust builds up to cause problems, the computers are at least 3 years old, usually 4 or 5. a five year old computer is out of warentee, and according to the company out of its usefulness lifespan, and therefore needs replacement, by a new expensive machine that will also be worthless in five years.

DUST

ProBoner said:

DUST

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so they use negative to create dust......? i relly dont think theyd WANT to do that. care to elaborate?

positive makes dust, since it sucks more air in the dust gets drawn in and dumped on your pc, needs to be cleaned more

actually i believe negative has more dust because air seeps in little cracks and settles to make dust. Positive will not do that.

Zerileous said:

actually i believe negative has more dust because air seeps in little cracks and settles to make dust. Positive will not do that.

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yea thats the general consensus (sp?) around here.

i think another reason is to save money (less fans) and for some it makes thier pcs quieter, and i have to admit, my old 8100 is barely audible.

more in than out and more out than in will both pull dust in, just in different ways. i also think the big oem's dont care about dust because by the time there is enough to hurt the hsf (and therefor the porcessor/stability) your computer will be old and may "need replacement"

that said, a friend of mine's mom is still working on a 6 yr old computer that does not need replacement, so it could be that the oem's are doing it on purpose to ensure that buyers will purchase again soon... i wouldn't put it past them

im not sure that most of them use negative pressure. the old dell(p3 800) that my family has and an hp(amd 2600+) that a friend has both had either balanced pressure or maybe only slightly negative or positive. on both the dell and the hp, the only exhaust was through the psu. the fan placement at the back was actually used as intake and was ducted to the cpu heatsink.

In my opinion, the box makes use as few fans as possible.
For both less noise and to save costs. In most cases they
have only one fan exhausting the air near the HS&F.

Just repaired my friend's old P3 HP system and it
only has one fan with a 90 degree plastic vent drawing the air
from directly around the HS&F out the back. From what
I've seen this type of flow config is pretty much normal for stock
boxes. They aren't Overclocked and need less cooling than our
stressed rigs.

Just my two cents.

are you sure the fan was pulling out of the case? i am not positive, but i think in the hp and dell computers ive seen, the fans attatched to the 90 degree ducts were blowing into the case.
if you think about it, if the case fan was sucking air out, the fan on the heatsink would be struggling to get air onto the heatsink

With low airflow generated by a single low-RPM exhaust fan, there won't be as much dust as in more typical custom PCs.
The single exhaust fan is probably the most efficient scenario in low-end cooling. Compare it to having a single (front) intake; the intake will blow some random air into the case, which will seep out anywhere. Not much air is moved where it is needed most -over the CPU. The sole exhaust fan focuses the airflow much better. It's probably also less noisy to the user, because it is located at the back of the case.

right on the head, noise is in hte back. tehy dont care much for coolinhg or dust, if iether become a problem the warentee is already expired and they will just make htre user buy a new one. if the warentee isnt expired, tehy'd charge to fix it and do a **** poor job of doing so.

id say negative pressure is better... I have 10 fans in my case (one in the front blowing in, one in the bottom back blowing in, two next to the cpu blowing out, two in the psu blowing out (and the other 5... videocard and nb cooler and cpu and two around my hdds)


Ive done some testing... running seti for an hour and my current setup is the coolest of all the combinations I tried... there are 2 intake and 4 exhaust.... every time I changed one of the exhaust into an intake the temps in my computer went up. any combination other then my current one went up at least 2-3C.

like Vio1 said, configuring your fans is a matter of testing and retesting for what works best for you. i used to have a top blowhole exhausting the hot air, but i turned it around so now all 3 case fans are intake (PSU is still exhaust) and i got a 2C drop to 34C load. to balance it out though i had to remove one of the drive covers so the air has somewhere to go, and i really can feel it move. so youhave to do some testing for yourself to see what it better.

I Know that the avionics in the helicopters we have use negative airflow to cool the "black Boxes". So if the the aviation comunity uses negative pressure and OEM does maybe there on to something

they're on to spending money to clean stuff out. woo! dust. yummy.

skitlets said:

if positive pressure is generally better, ie more intake air than exhaust, then y do the big oems usually use negative pressure. Usually its only one exhaust fan. im sure the big companies spend lots of resources making sure their pc's are going to last awhile, because no one wants thousands of angry callers saying their computer broke. so if positive pressure is better, why do the big guys use negative?

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Big companies use the rule of "GOOD ENOUGH"... They set standards, then once those standards are met they no longer need to expend any more time or resources on the subject. You can't have every Joe Sixpack in your organization making decisions for themselves; this keeps things working smoothly and economically.

I wouldn't recommend that anyone misconstrue their use of a single exhaust fan as a universal indication that exhaust is better than intake though.

In truth, it really doesn't matter which kind of pressure you have in your case unless you are using filters with the intake fans. If you are using filters then you want to have positive pressure - this way no dust can get in through fans and no dust can seep in through cracks or openings.

If you don't use filters, then + or - pressure will both create dust.

Overall, your first consideration should be total airflow - are your fans working together well? (Typically this should mean that you have close to neutral pressure) After that, unless you are going to filter your intakes, you are fighting a losing battle against dust.

Originally posted by Zip22

are you sure the fan was pulling out of the case? i am not positive, but i think in the hp and dell computers ive seen, the fans attatched to the 90 degree ducts were blowing into the case.
if you think about it, if the case fan was sucking air out, the fan on the heatsink would be struggling to get air onto the heatsink

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Dell's and HP's both exhaust with the duct... There is only one fan incorporated with the duct, not a case fan and a HS fan so there is no struggle for air. The single fan pulls enough air to cool the HS sufficiently and at the same time is exhausting the case air.

Re: Re: If positive pressure is generally better...

IMOG said:

[...]
Dell's and HP's both exhaust with the duct... There is only one fan incorporated with the duct, not a case fan and a HS fan so there is no struggle for air. The single fan pulls enough air to cool the HS sufficiently and at the same time is exhausting the case air.

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Yes, that's right - the Dell 2GHz P4 at my feet has 1 exhaust fan and no HS fan. There's a very nicely shaped green plastic duct from a double opening in the case to the HS. 0.84 watt fan, looks like 92 mm, in the duct.

It's a great way to go because it makes sure the HS is not getting any air heated by the heatsink already.

So you can get away with very minimal fans.

Of course, dust will build up in the case, since there are no air filters. But I'm guessing Dell doesn't regard that as their problem.

the wesson

my friend has an hp pavilion 735n with an amd 2600+ it has the duct connected to the case fan and the stock amd heatsink/fan combo.