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Direction of Bottom-mounted PSU fan

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Which direction do you mount your bottom-mounted PSU?

Total: 86 votes (47 blank votes)

  • PSU fan facing up (sucks air from case, through the PSU, and out the back)
  • 40 %
  • PSU fan facing down (sucks air from outside, through PSU, and out the back)
  • 60 %
April 5, 2010 8:51:07 PM

I'm curious as to the direction people like to mount their PSUs. Assuming the computer case mounts the PSU at the bottom of the case and there's a cutout at the bottom, which direction do you mount your PSU?

That is, do you mount it so the PSU's fan is facing up and sucking air from the case then exhausting it out the back? OR, do you mount it so that the PSU's fan is facing down and sucking air from outside then exhausting it out the back?

Has anyone run tests to see which performs better in terms of cooling the case? I would think having it face up and sucking air out of the case would be better.
a b ) Power supply
April 5, 2010 8:52:44 PM

You really want to be pulling the cooler air from outside of the case into your PSU and out the back. Your PSU will get very warm if you are pulling HOT air straight off your GPU in the other orientation. That is why they have the fan opening on the bottom of the case, and part of why they made the move to putting the PSU on the bottom to keep them a little cooler.
a c 77 ) Power supply
April 6, 2010 12:17:31 AM

There have been a few studies done on the benefit of either direction and it showed little or no difference between the two. I have my Corsair facing up into my Antec 1200 case and my system runs cool. Also, not all cases have bottom vents for your PSU, so you only have one option, which is facing up.
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a c 144 ) Power supply
April 6, 2010 1:19:49 AM

tecmo, you can always mod the case. I have three Antec 900's modded for cable management - three extra holes in the motherboard tray. It's hardly more complicated to cut a hole in the bottom of the case.

I orient the fan upwards toward the interior of the case. I figure that that fan helps keep the hard drives cool. I have never seen an HD temp over 29 C.

The three PSU's are 550 and 750 watt Corsairs and a 550 watt Antec. All three are working at 50 - 60% of capacity. PSU exhaust air is no more than 3 C over ambient. So I am not worried about internal case temps.

The GPU is another matter. :) 
a b ) Power supply
April 6, 2010 3:30:39 PM

It depends on your internal case temps to some extent I guess. It probably doesn't matter which way if your case temps are low, but if your case is getting warm, it'll be much better for the PSU to be getting ambient outside air.
April 6, 2010 8:56:36 PM

tecmo34 said:
There have been a few studies done on the benefit of either direction and it showed little or no difference between the two. I have my Corsair facing up into my Antec 1200 case and my system runs cool. Also, not all cases have bottom vents for your PSU, so you only have one option, which is facing up.


Can you link those studies? I've tried googling for some but couldn't find any articles on this matter.
a c 77 ) Power supply
April 6, 2010 11:56:04 PM

Chynkinese said:
Can you link those studies? I've tried googling for some but couldn't find any articles on this matter.

I'm trying to find where I saw the studies... I remember seeing some but I didn't bookmark them and can't find them easily by Google. It had been a while ago when I saw them.

I did find a forum post from Tom's that showed temperature difference when a Poster performed a test.... http://www.tomshardware.com/forum/275051-28-bottom-moun... It showed a 6C difference in CPU temps, but as Shadow703793 said, it could've been causing a negative air flow issue.
a b ) Power supply
April 7, 2010 4:04:53 PM

My question is, why change to bottom mounted PSU's unless in an attempt to keep the PSU cooler by getting it fresh air instead of warm case air? What other benefits are there of a bottom mounted PSU?
April 7, 2010 6:21:42 PM

flyinfinni said:
My question is, why change to bottom mounted PSU's unless in an attempt to keep the PSU cooler by getting it fresh air instead of warm case air? What other benefits are there of a bottom mounted PSU?



...maybe you can drag your computer around the living room floor to pick up dust? That could save you vacuum cleaner money to spend on canned air! :D 


Answer for the poll: Intake from the bottom of the case, and out the back. Just make sure your case has feet.
a b ) Power supply
April 7, 2010 6:32:07 PM

Lol- Thats why I have it up off the carpet on wood:-)
April 8, 2010 2:34:55 AM

I prefer to have the psu get cooler air from inside the case and blow out the hot.

This is of course the fact that the psu have its own compartment and has cool air entering it.
a b ) Power supply
April 8, 2010 3:57:38 PM

When it has its own compartment like that- I think the debate changes a bit.
April 8, 2010 5:55:24 PM

soundefx said:
I prefer to have the psu get cooler air from inside the case and blow out the hot.

This is of course the fact that the psu have its own compartment and has cool air entering it.


For the sake of the poll, I would consider that as getting air from the outside. That is to say, it has its own fresh supply of cool air and it doesn't share air with other computer parts.
October 18, 2010 6:37:05 AM

I'm a little late with this one, but my antec 1200 has no bottom opening so the psu fan is facing up, although my motherboard mounting backplate has more holes apparently than other antec 1200 cases, I bet there are a number of model versions. either way if your worried about case temps just snap the side mounted window fan on and it will cool your psu and everything else down a bit :D 
October 18, 2010 7:15:12 AM

Well, my PSU fan are facing the side case, which have holes on it. Where does that stand in the category?

The most important thing, AFAIK, is to have proper ventilation(duh!), regardless of the direction. PC case makers, especially the famous ones, didn't make their products without testing it. Of course, as jsc said, we can always mod it.

It will definitely be a non-issue if the case has its own compartment. But I don't think every bottom mounted PC case out there have this particular feature.

CMIIW, I'm all open for insight and knowledge sharing. We learn new things everyday.
a b ) Power supply
October 18, 2010 8:57:35 AM

I'm curious why it's a debate when it's bottom mounted, and yet when the PSU is top mounted it's not even a consideration?
October 18, 2010 9:10:59 AM

cmcghee358 said:
I'm curious why it's a debate when it's bottom mounted, and yet when the PSU is top mounted it's not even a consideration?

Maybe because if it's top mounted, the top side doesn't reach the floor?
a b ) Power supply
October 18, 2010 9:15:13 AM

It reaching the floor would entice me not to point the fan towards it, as the limited space would inhibit airflow into the PSU, thereby increasing it's operating temperature and lowering it's output.
a c 91 ) Power supply
October 18, 2010 9:18:45 AM

'It doesn't matter' option is missing.. The whole idea of a bottom mounted PSU arrangement is to help with cable management and works best when the case has a top exhaust fan or atleast grills to pass out the rising hot air..
October 18, 2010 9:19:09 AM

@cmcghee358: +1 To that. That's why it's worthy to be discussed. As for top mounted PSUs, the concept is clear, with everyone (well, maybe) agrees to it. An additional insight for me, by the way. Thank you.

@emperus: Another insight. Although the "it doesn't matter" part is not what I have in mind. But good point nevertheless.
October 18, 2010 10:45:12 AM

Yeah it does not matter to me - cable management and air flow is more important. If the thing makes the case hotter then change it or the cable looks awful then change it.
May 13, 2011 10:14:13 PM

I realize this is an old thread, but I wonder how many of you actually read the articles at Tom's Hardware? Tom's covered this issue in 2008. Cases with a bottom mounted PSU is a poor design, but some moron came up with the idea, it somehow caught on, people started asking for it, so the manufacturer's started building them that way.

The whole idea is to provide a dedicated fresh air source for the PSU, that means the fan should be at the bottom. There are numerous problems with this design. The 1st is dust. As was mentioned above, you're basically creating a vacuum cleaner. Any dirt, dust, hair, crumbs, bugs, etc that get near the base of the case will get sucked into the PSU, eventually clogging the fan & heatsinks. Also, the top of the PSU will get hot, that hot air will rise & what's directly above it? The video card. Now more heat is being added to a card that usually has barely adequate cooling of it's own. So what do you do? Add more case fans! Yeah, that's the ticket. How about 2-120mm intake in the front & 2-120mm exhaust in the rear? So what if it sounds like a 747 when you fire it up? At least the temps are low - or are they?

A decent case with a top mounted PSU & ONE 120mm rear exhaust fan USED to be more than adequate for all but the most extreme systems. But now that the PSU has shifted to the bottom, more fans are needed. Oh yeah, & don't forget cabling problems. Some PSU cables simply aren't long enough. So while you're ordering up that cool new bottom mount case, you'd better check your PSU cables, because another upgrade may be in your future. Isn't that wonderful? I'm so glad all the smart asses got together & begged for the bottom mount design.
a b ) Power supply
May 13, 2011 10:31:16 PM

jamx13 said:
I realize this is an old thread, but I wonder how many of you actually read the articles at Tom's Hardware? Tom's covered this issue in 2008. Cases with a bottom mounted PSU is a poor design, but some moron came up with the idea, it somehow caught on, people started asking for it, so the manufacturer's started building them that way.

The whole idea is to provide a dedicated fresh air source for the PSU, that means the fan should be at the bottom. There are numerous problems with this design. The 1st is dust. As was mentioned above, you're basically creating a vacuum cleaner.

That's why there is usually a removable (and thus cleanable) filter at the bottom of the cases. :pfff: 
!