Given an option, should PSU pull air from inside or out?

[TopGun]

Hey guys,

Can someone please explain why, given an option, would someone want to pull air from inside the case vs. turn the PSU "upside-down" and pull air from outside the case (bottom mounted of course).

Some things I'm just guessing or have questions about...but feel free to add more I haven't mentioned...

-right side up...would help pull warmer air out of case?
-is the PSU supposed to be fan side up (like by manufacturer's specs?), or does it matter at all (longevity-wise or functionality-wise)?
-upside-down...pulling air from outside the case in its own closed loop...does this keep the PSU cooler and last longer/function better than from pulling through warm case air?
-upside-down...does this help you keep more inflow of air from your case fans?...I read somewhere you want more inflow of air than outflow to keep the interior pressure up to help keep out dust from coming in through cracks or holes that don't have filters?

My guess is that for whatever reason it's better to pull from outside...based mostly on why would case manufacturers be making this a feature if it's not the better option?

Enlighten me with your wisdom gurus.

Thanks,
-TG

P.S.-I apologize for my wording...I'm having difficulty trying to phrase this correctly.

 

[Leaps-from-Shadows]

The only reason to pull air from inside the case is if the case has a bottom mount for the PSU but doesn't have cutouts in the bottom of the case. Some are still made like that.

The main reason we do the bottom mount is to pull cooler outside air through the power supply, maximizing the cooling effect. The cooler the PSU is kept, the more power it can pump out, the more efficient it is, and the longer it will last.

 

[TopGun]

I was asking because I was going to do a cutout in the bottom of my new case (cheap one for experimenting on) if it was better for the PSU...and probably not bother if it made no difference or if it was better to draw from the inside.

Speaking of which, if anyone could link some instructions/vids on how exactly to do this (preferably with a removable air filter too), that would be great.

 

[JackNaylorPE]

The ideal method is the one used by Antec in their P193 / P183 series.

As you can see here, the PSU area is completely isolated from the rest of the case

http://www.newegg.com/Product/ImageGallery.aspx?CurImage=11-129-174-Z02&ISList=11-129-174-Z01%2c11-129-174-Z02%2c11-129-174-Z03%2c11-129-174-Z04%2c11-129-174-Z05%2c11-129-174-Z06%2c11-129-174-Z07%2c11-129-174-Z08%2c11-129-174-Z09&S7ImageFlag=1&Item=N82E16811129174&Depa=0&WaterMark=1&Description=Antec%20Performance%20One%20Series%20P183%20V3%20Black%20Aluminum%20%2f%20Steel%20%2f%20Plastic%20ATX%20Mid%20Tower%20Computer%20Case

They also have the intake and exhaust on PSU as a straight thru run thru the PSU.....no 90 degree angle resulting in less turbulence, better cooling and less noise.

silentpcreview commented on the "integrated design" of these cases (1200, DF-85, P193, P183) and the CP series PSU's in their review of the CP-850 but I can't bring it up as their site is down atm. Here's the cached version

http://74.6.238.254/search/srpcache?ei=UTF-8&p=silentpcreview.com+CP-850&fr=moz35&u=http://cc.bingj.com/cache.aspx?q=silentpcreview.com+CP-850&d=4588227856237604&mkt=en-US&setlang=en-US&w=249ab0d0,5eacb211&icp=1&.intl=us&sig=95HGmEnxPfJg81WbRJjwgw--

A serious consideration is that in each of the three [now four] compatible Antec cases, the CP-850 mounts on the bottom, and the intake for the PSU is quite separate from the rest of the system. In the P193 and P183, the PSU is in an entirely separate thermal chamber, and in the model 1200 [and DF-85], a direct path can be maintained to the directly opposite, wide-open front vent. This means that our extreme hot box test conditions never apply to the CP-850; in other words, SPCR's test environment is unrealistically hot for the CP-850. Our atypical spot check with a room ambient thermal test showed the CP-850 would reach only 24 dBA@1m at 700W load in a 27°C working environment. This is ridiculously quiet for such high power output.

The above is an obviously unfair advantage for the CP-850... but what of it? Antec has used an integrated systems approach for its CP-850 and its best cases, and if that approach is an advantage over all other case/PSU combinations, then, all the more power to Antec! It's not uncommon for enthusiasts to frequently replace the motherboard and components that mount onto it — such as CPU, RAM and video card — while the case and PSU are retained. There would be ample reason to take that approach with the CP-850 and one of the compatible Antec cases.

 

[mosox]

It's good because of the dust the PSU gathers from inside the case if at the bottom with the fan up. Also it impedes the airflow especially if you have expansion cards. But in order to use it the other way around you must have case legs and those shouldn't be too small.

 

[TopGun]

Best answer selected by TopGun.