# PSU at the top or bottom?



## Octopuss (Feb 11, 2011)

Most cases have the PSU mounted at the top of them. Some have it at the bottom though. Is there any benefit in the latter? I always thought hot air raised up, which would make top-mounted PSU more logical. So how is it?


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## Fourstaff (Feb 11, 2011)

Bottom mounted PSU is better for cable management. The amount of benefit due to "hot air rises" is at best a few degrees.


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## Solaris17 (Feb 11, 2011)

most good PSU's exaust themselves my corsair hx 1000 has a fan on the bottom and back in from the one on the bottom exaust out the rear. its bottom mounted in my xig so it pulls cold air. i dont think it gets hot really but i think its more efficient personally but im a stickler for airflow.


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## t_ski (Feb 11, 2011)

Two main benefits:

1. PSU fan often intakes from the bottom of the case, drawing in cool air.  This results in a more stable PSU.
2. A *QUALITY* PSU will weight at least 7 pounds, and having it at the bottom of the case lowers the center of gravity.


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## Fourstaff (Feb 11, 2011)

Intake from the bottom is not a very brilliant idea though, it sucks in all the dust.


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## Octopuss (Feb 11, 2011)

Fourstaff said:


> Intake from the bottom is not a very brilliant idea though, it sucks in all the dust.


Besides, it has llittle to no room to actually suck the air from. I have Antec P182 and there is like 5mm between the PSU and bottom of the case


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## jsfitz54 (Feb 11, 2011)

I'm a PSU on top fan.  Cool air comes in the front, down low, sweeps across the mobo and exits out the top rear.  Sometimes it's hard to improve on a solid design.  That being said, cases have advanced over the plain box with lots of extra fans, side vents, top vents and other improvements.

If your case has many of the improvements then I would say it makes little difference which way you go.


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## HXL492 (Feb 11, 2011)

Fourstaff said:


> Intake from the bottom is not a very brilliant idea though, it sucks in all the dust.



Most cases that feature a bottom mounted psu usually come with a dust filter



Octopuss said:


> Besides, it has llittle to no room to actually suck the air from. I have Antec P182 and there is like 5mm between the PSU and bottom of the case



Well some cases, like for example the CoolerMaster 690II Advanced comes with enough clearance under the case for air to be sucked in. I guess you would need to pay attention to the design of the case

Overall I would aim for a bottom mounted psu design as it draws cooler air from the outside and usually psu's run 'better' when cooler


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## twilyth (Feb 11, 2011)

I like my Antec 300 with the PSU at the top and with a top exhaust port better than the P180 with the PSU in a bottom compartment.

If you have a PSU with modular cabling I don't think it makes much difference.  Having the PSU at the bottom lowers the center of gravity if there is a chance of someone bumping into your rig.


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## AsRock (Feb 11, 2011)

I like the PSU at the top makes no sense to have them by a hot v card.  How ever like said some cases have a area on the bottom to allow cool air in.

I would like them start doing the same thing with PSU's at the top.  In my case the PSU is at the top sideways and if it was not due to how my PSU is designed i would of made a vent on the right side of the case so it could suck air in.

All though my case at the top is vented and been thinking about making a funnel for it so it can get air from out side just never got around to it lol.


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## Octopuss (Feb 12, 2011)

On completely offtopic note: anyone else pissed at the fact that there are barely anymore cases with green power led and red HDD one?


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## Fourstaff (Feb 12, 2011)

Octopuss said:


> On completely offtopic note: anyone else pissed at the fact that there are barely anymore cases with green power led and red HDD one?



Probably because it is pointless to have them anymore. You can hear the sound when the PC is on, and you will need 10 lights if you want to monitor HDD activity.


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## Octopuss (Feb 12, 2011)

10 lights? How do you mean? 
I still like to check whether the PC froze up or not at times by the way (not too often, yeah, but still). 
Guess I am old-fashioned too.


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## Bo$$ (Feb 12, 2011)

Fourstaff said:


> Intake from the bottom is not a very brilliant idea though, it sucks in all the dust.



i have first hand experiance with this, even with a filter, dust is uncontrolable!


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## Frick (Feb 12, 2011)

Bo$$ said:


> i have first hand experiance with this, even with a filter, dust is uncontrolable!



Not if you have it hanging 20 cm from the floor.


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## _JP_ (Feb 12, 2011)

But if that was the case, wouldn't there be an issue with the amount of air-flow available?


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## micropage7 (Mar 13, 2011)

one that is not nice on bottom placed psu is it need longer cable coz usually 24 pins placed on top right of the board so not all psu could acomodate this


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## AsRock (Mar 13, 2011)

I like top better but they do not put the effert in cases like they do with bottom placed PSU's.  For example they make a vent for them to draw air from the bottom of the case.

If i had a 120mm fan type PSU i would made the vent my self and it be better at the top or in my case it be at the side or but with my PSU it would have to be a funnel to the top of the case.

So if ya have a 120mm fan type PSU and handy with cutting tools PSU at the top be best as PSU's do get hot and there be less dust possible issue's..

Why the hell would ya want a a 25c-60c PSU by a v card beats me silly lol.


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## GSquadron (Mar 13, 2011)

The cable sometimes cannot reach the bottom one


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## Octopuss (Mar 19, 2011)

AsRock said:


> I like top better but they do not put the effert in cases like they do with bottom placed PSU's.  For example they make a vent for them to draw air from the bottom of the case.
> 
> If i had a 120mm fan type PSU i would made the vent my self and it be better at the top or in my case it be at the side or but with my PSU it would have to be a funnel to the top of the case.
> 
> ...



I think there are a few good points in your post but I can't understand a word.


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## Spectrum (Mar 19, 2011)

Octopuss said:


> Originally Posted by AsRock
> I like top better but they do not put the effert in cases like they do with bottom placed PSU's. For example they make a vent for them to draw air from the bottom of the case.
> 
> If i had a 120mm fan type PSU i would made the vent my self and it be better at the top or in my case it be at the side or but with my PSU it would have to be a funnel to the top of the case.
> ...



I have a bottom mounted psu and it's a good 4 inches away from my card... however i can imagine that with an SLI or crossfire solution that'd increase video card heat a couple degrees.

As for those of you talking about dust... bottom mounted PSUs take in so so much dust... i've got a cm690 and even with a filter... the inside of the psu is covered in dust. the filter is completely covered aswell.


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## Melvis (Mar 19, 2011)

TOP, better for air flow to draw the hot air out (hot air rises after all) Use it as another exhaust fan.

Less build up of dust been at the top over the bottom. (PSU with lots of dust isnt a good idea)

Some PSU wont reach the CPU connector on the board over a top mounted PSU.

Just MHI


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## neoreif (Mar 19, 2011)

My Thermaltake V3 Has a bottom mounted PSU and the case came with a dust filter. Its true for me that bottom mounted PSU's suck more dust cause the PSU's cooling fan draws air directly from the outside and here is where the dust filter comes in. All I have to do is just clean the filter once every month to make sure that the PSU gets ample cold air from the outside. Checked the PSU itself and it seems that minimal dust accumulated through almost 9 months of use. So I guess with a good dust filter, I'd go with a bottom mounted PSU!


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## qubit (Mar 19, 2011)

Fourstaff said:


> Intake from the bottom is not a very brilliant idea though, it sucks in all the dust.



Oh, does it!  I removed the PSU from my HAF922 the other day and there was a carpet of dust blocking the intake. Gross.

I've cleaned it off course.


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## uzuhl (Mar 19, 2011)

Octopuss said:


> On completely offtopic note: anyone else pissed at the fact that there are barely anymore cases with green power led and red HDD one?



Order your own power cables like these http://www.amazon.com/dp/B00213KDQK/?tag=tec06d-20


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## _33 (Mar 19, 2011)

I prefer the PSU located in the bottom of the case specifically because the PSU being there is on it's own air circuit, so basically it doesn't get hot air from the motherboard+CPU (if it were a top mounted PSU).  Also I would have to say the center of gravity being lower means it's easier to handle the case when I bring it elsewhere, but barely still.  For cable management I haven't got into any trouble being bottom mounted, it's not a flawed design imho and it does make a lot of sense.  Now, if your PSU (with filter supplied in the case) accumulates a dirt layer like a carpet of dust, then I would ask myself some serious questions about the rest of the room where the computer resides.  I am not a swiffer fanatic and I must tell that my computer isn't filled with dust and what not.  But say, if you can't tell if you have light coming from that front mounted 120mm led fan, then you might have some concerns.


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## cever89 (Mar 31, 2011)

I would say a bottom-mounted PSU is much better for thermals. Also as someone already mentioned, the lower center of gravity makes your case much more stable. The only caveat would be for those that have super big cases to make sure their cables are long enough to reach their components. Of course, there are plenty of cable extensions out there - and some nice looking ones too!


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## sic_doni (Apr 5, 2011)

I think PSU in the bottom should be the best one 
it looks better and feels like more space inside the case


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## lilhasselhoffer (Apr 5, 2011)

*Do the Math*

Hello,

Beyond the fanboy, and personnal experience stories; the placement should be relatively simple to calculate.  Think of this in terms of lost energy, and that 99% or more of all lost energy is converted into thermally dissipated power.

PSU = 80%
650 watt draw = 812.5 watts from wall = 162.5 watts TDP
850 watt draw = 1062.5 watts from wall = 212.5 watts TDP
PSU = 85%
650 watt draw = 764.7 watts from wall = 114.7 watts TDP
850 watt draw = 1000 watts from wall = 150.0 watts TDP

If we assume that the processor has a TDP somewhere in the range of 100 watts (ballpark based on low as 65 and high as 130 watt TDP for Intel and AMD processors), we can find the maximum TDP of a GPU (or set of GPUs) that would warrant a top or bottom mounting for thermal reasons.  They vary so much that you should look online for what you have, not ballpark a figure.

SO:
If GPU TDP + CPU TDP > PSU TDP then you should mount it at the bottom, so maximum heat generation is at the top.
If GPU TDP + CPU TDP < PSU TDP then you should mount it at the top, so the maximum heat generation does not influence the rest of the items in the case.
Finally, consider the dust a thermal insulator.  As such, if GPU TDP + CPU TDP ~= PSU TDP (within 10% or so) you should mount it at the top to minimize the amount of dust that is sucked into the case by the PSU.


A little bit of foresight, assuming a couple of future upgrades increasing thermal generation (woo hoo next gen of GPUs!) and wiring lengths, and your answer should be relatively clear.  This is why some people prefer the bottom, and some people prefer the top.  There are cases where both work well, and additional aesthetic reasons, that have little influence on performance that people base their preference on.


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## Melvis (Apr 5, 2011)

@lilhasselhoffer so you answer is top or bottom?


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## X1REME (Apr 5, 2011)

A psu will produce more heat and get hotter when at the bottom, will also require an extra/or faster fan on the case...

All depends on the *Case Airflow*; my case is optimized to be on top


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## thebluebumblebee (Apr 5, 2011)

The location of the PSU within a case does not determine how hot it gets, how much heat it produces, or how much dirt is drawn into the case.  4 things determine how hot a PSU gets and how much heat it produces: efficiency, load ,airflow and the temperature of that air.  If you take a case that has a bottom mounted/bottom intake for the PSU and put it on deep carpet, you will have a problem with airflow for the PSU.

A PSU should not be considered an exhaust fan.  Heat is a determining factor in the life of a PSU.  Why would you want to have the system heat going through the PSU?

BTW, I think the standard ATX tower case is a poor design for heat dissipation.  That is why I am a fan of the Silverstone Raven and Fortress cases.  Their price seems high until you consider the fact that there are no more fans to purchase.  I recently bought an inexpensive case and then proceeded to spend more on additional fans than the case cost.

If my choice is between top or bottom mounted PSU's, I'll take bottom.  But make sure it's a well designed case with cable routing in mind.


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## lilhasselhoffer (Apr 5, 2011)

Melvis said:


> @lilhasselhoffer so you answer is top or bottom?



My apologies for not making it clear.  Neither answer is correct, but neither answer is wrong.

I prefer lower TDP CPUs and a single mid-range graphics card.  I've thus chosen a case with a top mounted PSU.


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## Brandenburg (Apr 5, 2011)

Octopuss said:


> 10 lights? How do you mean?
> I still like to check whether the PC froze up or not at times by the way (not too often, yeah, but still).
> Guess I am old-fashioned too.



thought i was the only one..  just like to "see" my machine working


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## Peter1986C (Apr 5, 2011)

Brandenburg said:


> Octopuss said:
> 
> 
> > 10 lights? How do you mean?
> ...



At my student room, there is a vent system that makes so much noise that my Seagate HDD is barely hearable. So I am among you two.


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