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Top or bottom mount PSU?

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Last response: in Systems
June 10, 2009 2:11:11 PM

I'm considering picking up a new case and need opinions on what people like better. The top mounted PSU or the bottom mount PSU? I've had both and the top mount seems to be better to me. It seems that most mobo's are set-up for them to work better and it seems that having the heat already being at the top and not having all of it rise over the rest of the components would seem to be the smart choice. But it seems like a lot more cases are going with the bottom mount. Maybe it's just my PSU that seems to have trouble reaching all the connections but I have a feeling it's not.

More about : top bottom mount psu

June 10, 2009 2:47:19 PM

IMO, and what most people like are the bottom mount PSU. One reason is that when the PSU is mounted on the top it can make the case top heavy, so the extra weight on the bottom instead of the top is always nice.

Another reason I like it is that if you can find a good PSU with a fan on the bottom of it, most cases that have okaces for the PSU on the bottom also have vents on the bottom where the PSU go. That will allow you pull air directly from outside your case into your PSU which will keep your PSU cooler and wont have so much heat in your case.

Again, them are just my opinions. Other people might like it differently though.

June 10, 2009 2:54:00 PM

We have the same case so I at least know that your experiences are similar to mine. Do you have a modular or non-modular PSU? Mine is modular and I have to admit that I hate it. The cables seem a lot shorter than non-modular PSU cables that I've had in the past. That is my main issue. Maybe I just need to find a different PSU and try it in my case before I ditch the case.
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June 10, 2009 3:15:49 PM

Mine is a non-modular PSU, and it works perfect in the case I have. Well besides having a some extra unused cables that I have to find a place to put them so they don't restrict air flow, but that is not that difficult to do.

I thought I had my PSU in my Sig specs, but it looks like I forgot it. Ill have to add it now that you mentioned it.


EDIT: Here is the PSU I use, and have not had any problems with it so far. I always try and get a corsair brand PSU. Ive never ran into any troubles with them.
June 10, 2009 10:04:30 PM

I, too, have the CM690, whose PSU is bottom-mounted. I've done dozens of custom builds, and I prefer bottom-mounted as to top-mounted. I'm not sure why, seems just to be a personal preference.
a b B Homebuilt system
June 10, 2009 10:50:35 PM

Top mounted psus are:

- Easier on cable lengths and cable management.
- Theoretically harder to keep cooler
- Make most cases top-heavy.

But (except for cable lengths) it almost always depends on how the case deals with things, not just the psu.

Bottom-mounting the psu solves top-heavy and any cooling "problem". I think bottom mounted gets preference because cable management can be fixed with wire extensions (or ignored).

OTOH, I prefer top-mounted and tend to look for cases that do that properly.

Recently, though, the ability to get large video cards in a smallish case while maintaining temps with quiet air flow trumps all the other "concerns" for me.
a c 90 B Homebuilt system
June 11, 2009 2:14:31 AM

If your psu has a top/bottom intake fan like the corsair, then a top mount can be a bit of a problem. Most cases do not supply fresh air to such a psu through the top of the case. Then, the psu cools itself with a supply of hot air that escapes from the cpu. That makes the psu fan run faster, and noisier.
With such a case, I would prefer a psu like the PC P&C units which get their cooling air from the rear where you have the possibility of getting some cooler front intake air.

A bottom mount is ok with either type of psu cooling.

@3o0ch: Why are you looking for a new case? What do you want it to do that is different?
June 11, 2009 4:38:12 PM

I recently built my first machine, and went w/ the antec 300 case that has the psu at the bottom. For all the reasons posted above, I absolutely love it. It looks very clean w/ the psu at the bottom. With the case opened up, it's like everything is easyier to see and get to. Also, my pc will eventually be mounted under the desk, so having the mobo higer up, and consequently all hte i/o ports higher up on the case makes attaching external devices a bit easier.

I don't know about cooling- imo, it seems to me w/ the psu at the bottom, it will draw cool air in through it's massive fan, keeping itself cooler, than if it were mounted at the top, drawing in warm air. And that psu fan is so freakin' big, I don't see how any significant amount of heat it'll add to the ambient temp in the case anyway.

Also, I've got a few gripes with the wiring, mosty the sata power connectors that came w/ my thermaltake modular psu. The connectors are arranged to come down from the top of the case, so in my case (pun) the wires come up from the bottom, so they reach the drives upside down. They can't be flipped over. So, I've got this big loop-de-loop of wire to get juice to my hdd. That and hte 8pin mobo cable has to cross over my video card and pass right in front of my cpu hsf. I've got extension cables and sata y connecters to clean that all up on my newegg wishlist/price watch. I don't want to spend $7 shipping on $14 of product- or I'll try to hunt them down locally.

June 11, 2009 5:29:30 PM

It's a well known fact that hot air rises up.the psu is one component that generates a lot of the top mounted psu case would be my preference.
if you buy a bottom mount psu case then the hot air will increase the tempp inside the case.
so buy a top mounted case......
but its my personal opinion.I have never tried a case with bottom mounted psu.
June 11, 2009 5:36:27 PM

Hot air rises up- BUT- there's a gigantic 140mm fan in my psu sucking it all back down and blowing it out the back of my case.

I hold my hand about an inch above my psu w/ the pc running and I feel nothing but cold air. Heck, w/ that antec case, no matter where I hold my hand I feel nothing but cold air. But- then again, I haven't really put it through it's paces yet. I've yeet to see how it handles batch processing a few hundred raw photos in lightroom...

a b B Homebuilt system
June 11, 2009 9:01:52 PM

Did you guys know that all air molecules are in random constant motion, and it is theoretically possible for all of it to move to one corner of your room so you suffocate in your recliner?
June 11, 2009 9:20:55 PM

I havent put it in yet, just got it shipped, but a few reviews specifically note that the cables are a little longer, and the PSU itself should be a great, quiet, solid build:

Edit- Guess I'll answer your question though haha. I very much prefer bottom mount PSU. As long as your cables reach where you need them to, you have every reason to put it on the bottom. Especially if the fan is on the back and your front case fans are directly across from it (cooling your HDD's) its great airflow.
August 18, 2010 11:25:49 PM

From all of the threads that I have read concerning the placement of the PSU, and some high school level science, I feel that I have come to a decent understanding of why someone would put the PSU at the bottom. I also want to comment about cases that come with a PSU versus not.

Working on the base concept that heat rises, one would first hesitate at the thought of having the PSU at the bottom of the case. Logically, why would you want warm air coming off of the PSU and rising across your components? As I understand it, the PSU sucks air from inside the case and blows it out of the case. This would cause the heat of the PSU to be blown out of the PSU, sucking air from
the bottom of the case.

My next point is if you are concerned about the placement of your PSU, you probably are building a decent machine. Otherwise, you would have gone to DE11 and just got a desktop computer for surfing the internet.

Following that thought, of why you are even concerned about the placement of the PSU, leads me to believe that you are going to be building a more powerful machine. This being said, you will probably be buying a more powerful PSU. The point of the PSU is not to cool your system, but to rather power it. That is what the other case fans are for. Being that you are using a more powerful PSU, and it isn't it's job to cool the case, you would want the PSU to keep itself cool and not contribute to the problem. If you had the PSU at the top of the case, knowing that heat rises, the PSU would not only have to take care of itself, but all of the heat generated by the other components, which are requiring more power, thus more heat...

The next step in this logic. You are building a more powerful machine, which probably means that you are putting in larger PCIe x16 cards (one, two or even three). The sheer size of these, and the fact that they have their own fans for the GPUs tell me that these are a major factor into the heat of your system. Also, these boards are towards the bottom of your motherboard. I can logically see hot air getting trapped under the video cards, seeing as air is being blown in from the bottom front, and sucked out at the top rear. Having the PSU at the bottom would logically help pull air across the video cards, giving the hot air somewhere to escape. Now, this does place some of the heat from the video cards onto the PSU as a burden, but at least it is not all of the heat of all of the components.

Coming close to a close, those who claim that the PSU at the bottom changes how much dust gets into your computer may not have thought this through fully. Maybe the dust collects more at the bottom, rather then being spread across all of the components. Maybe this is a more efficient way of moving air in your case, causing your system to pull more air through. I really have a hard time believing that the position of your PSU in your case has anything to do with how much dust is in the air. I mean, the thought that having the PSU at the bottom of the case causes more dust follows the same thought process that maggots came from meat (High school biology lesson). Besides, you should be cleaning your case monthly seeing that static electricity is the #1 killer of PC components and dust is the #1 cause of static electricity (humidity also).

The last point concerning the PSU and heating, I have seen it argued that having the PSU at the top near the other drives keeps your heat creating components all together, and that being a problem. I don't see this as being an issue, because if you care where your PSU is, you probably have good video cards, and having it at the bottom puts it near those.

The last points concerning the PSU position that I have found substantial is that it makes the case less top heavy (which I could see as a problem in a full tower case) and it makes managing the cables much easier. (A big plus, considering having your cables managed better would help improve airflow through the case... instead of a rat's nest slowing things down).

The one significant complaint I have found about having the PSU at the bottom is the distance between the power supply and the power connector on the board. If you buy a case that requires the PSU be at the bottom, I suggest getting an extension cord for the power. I found a good one on a popular online computer parts store for $6.

Lastly, those who say that cases that don't have a PSU upon purchase are $**t haven't thought this through. Most PSUs that come with cases are generic ones that probably don't have enough power. If you care enough to worry about where the PSU should go, then you probably shouldn't be using the PSU that comes with a case. Now consider two cases that are the same price. One has a PSU the other does not. I would think that the one that does not would be a higher quality case for two reasons: The people that made the case understand that anyone serious about building their own machine will probably buy another PSU; and there was more money put into the construction of the case, rather than filling it with a generic PSU.

All this said, I found a great case. The Antec twelve hundred. It has a place for the PSU at the bottom, and at the top, where the PSU would have been, is a large fan, facing up, not back. This makes a gaping hole in the top of the case pulling the air up and out of the top, where, knowing that heat rises, the heat would naturally float to.

Hope This Helps,
NPE (Null Pointer Expert)
December 16, 2011 1:08:15 PM

barna madau said:
I recently built my first machine, and went w/ the antec 300 case that has the psu at the bottom.
Does the Antec 300 have a vent hole in the bottom under where the PSU goes?
January 8, 2012 11:47:54 PM

Have a look at the AERO COOL GAMING MASTER VXR Case. I have seen no other case as good for such a cheap price ($50) No horrible logo splashes across it, bottom mounted PSU (Having a bottom mounted PSU and all the normal fans means more air goes out instead of in, creating a partial vaccum which all PC builders know is preferable, as more cool air is drawn in through the vents) and all the drive bays you could ever need. ^_^
a c 121 B Homebuilt system
January 9, 2012 5:45:51 AM

Some points in no particular order:
The original PSU ATX spec depended on the PSU providing some case cooling. And in some of the early, low spec Dells, the only fan inside was the PSU fan.

I standardized on Antec 900 cases when they were one of the few true gaming cases. (Would probably use the Corsair 650 now.) It uses a bottom mounted PSU, but has no hole in the bottom of the case. I orient the the PSU with the fan facing toward the inside of the case. Even when the systems are running at full load, exhaust air is generally about 3 C above ambient and has never been more than 5 C above ambient. Hard drive temps are usually around 27 - 28 C. That tells that I do not really have a problem with the temps in the lower case.

Warm air naturally rises, but forced air cooling with fans will overpower natural convection.
a b B Homebuilt system
January 9, 2012 1:05:48 PM

Twoboxer said:
Did you guys know that all air molecules are in random constant motion, and it is theoretically possible for all of it to move to one corner of your room so you suffocate in your recliner?

That's the most ridiculous thing I've ever ... *gasp* ... *gack* ... *unnnggghhh*
February 27, 2012 12:31:54 AM

I'm researching my first build, and I think the best case scenario would be a top mounted PSU on a case with mesh in the top part of the PSU corner - that way it would work as most good cases with bottom mounted PSU and also resolve the hot air rising concern. Unfortunately can't find many cases like that.. I guess will have to increase my case budget.

Btw, some very good diagrams on here concerning airflows:
February 27, 2012 1:03:46 AM

Unless you are very clumsy or participate in indoor sports within proximity of your machine, I'd go with top-mounted.

I think the heat generated by the CPU being sucked through your PSU is the least of your concerns, as it really shouldn't be warm enough to cancel out the properties of the PSU (unless your heat-sink isn't sinking heat, in which case you have other problems).

The main problem I have found with bottom-mounted PSUs is dust. Dust is horribly cruel to electrical components and having a large opening pointing upwards allows a lot to get in when your machine is powered off. Secondly, as others have said, you may find the cable reach leaving a lot to be desired.
February 27, 2012 11:38:46 PM

Bottom mounted cases (good ones) have mesh on the bottom, so you face the fan down to the ground. They also often come in with filters. The only problems there is that you should have some clearance between the floor and the rig and you need a hard, even surface - not carpeting like in my case.
March 19, 2013 12:53:31 PM

Petrofsky said:
Twoboxer said:
Did you guys know that all air molecules are in random constant motion, and it is theoretically possible for all of it to move to one corner of your room so you suffocate in your recliner?

That's the most ridiculous thing I've ever ... *gasp* ... *gack* ... *unnnggghhh*

Absolutely not possible. as stated earlier, partial vacuurn does exist in rel life, no rnatter how "randorn" the rnovernent of each rnolecule, it will eventually be swayed by the lower density created in the lager/largest area with the fewest particles in it. once pressures in the space are stabilized, they would freely again go whichever direction they "liked," but ask anyone who has tried to create a vaccuurn, they will tell you it requires rnore than generous arnounts of effort(ie, try pulling a wet plunger off your bathroorn linoleurn after sinking it down as hard as you can, if you were inside that plunger, yes, you could get short of breath, and giardia:) 
a b B Homebuilt system
March 20, 2013 3:02:28 AM

In my opinion...

Bottom mounted PSU is good because:
1. Better air flow
2. The central of the weight is moved lower, this makes your PC mechanically more stable this way.

Bottom mounted PSU is bad, because:
1. Sucking go without filter...

April 26, 2014 2:05:01 AM

Does it reduce the health of a top mounted PSU cause its not normal to rotate the PSU's original face. Fan should be on the top accordingf to the Earth surface. The RPM of fan gets slightly slow sometimes.
a b B Homebuilt system
April 28, 2014 11:26:12 PM

In the linked picture? Definitly not.
The fan must face downwards, unless if there is no hole. :) 
April 29, 2014 9:28:02 PM

There's no hole!! :(  Do you know if the top-mounted PSUs' life gets shortened or not? Very confused,very.
a b B Homebuilt system
April 29, 2014 11:35:20 PM

Top mounted? Shortened PSU's life?
Theoretically, yes, due to temperature issues.
But, I do not know, how it is, in the real life.
All of my top mounted PSUs lived long too.