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Vertical vs. Horizontal Case Cooling
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Other Considerations

Cooling performance aside, there are a few physical challenges to vertical cooling.

  1. Having the air intake at the bottom turns the chassis into a vacuum for dust. If the system is not raised up off the floor, it will have a much larger dust problem than a traditional case as the intake fans are right at ground level where dust tends to congregate. Removable filters over the fans definitely helps, but in our experience it is rare that many people (tech literate or not) remembers to clean out the dust filters on their computer as often as they should.
     
  2. All the ports for the motherboard and any PCI cards will end up at the top of a vertical cooling case. This may or may not be a big problem for the end user depending on the positioning of their case. The exposed ports on the top of the case will also make your system much more prone to damage if a liquid is spilled onto the case than a traditional case with a completely or near-completely sealed top.
     
  3. Some components may not fit properly because most manufactures design for traditional oriented cases. For example, a long 5.25" device may not fit in the Silverstone FT02B-W as it may come into contact with a PCI card that is installed in one of the lower PCI slots.

Conclusion

In terms of performance, we were surprised by the results. Convection should (in theory) aid in cooling with a system running in a vertical orientation.  However, our measurements do not support that theory. The Antec P183 V3 showed our only large variance in cooling, but with the horizontal orientation running cooler. So what is causing these results?

Our conclusion is that the forces of convection in a computer are simply not strong enough to overcome even the turbulence and airflow eddies caused by the fans. The lack of any temperature variances when we tested with the air-cooler supports this theory, as air-coolers contribute more airflow and turbulence to the core of the system than a closed-loop liquid cooler (which only has a fan at the edge of the system). The fact that the Coolit ECO II in the Antec P183 V3 was running hotter in the vertical orientation does suggest that the hotter air in a system tends to congregate in the top of a system, but it appears that this is only the case when the air is relatively stagnant (no fans in the area). We believe that this result did not replicate in the Silverstone FT02B-W simply because the airflow in that case is so unrestricted that there is not this pocket of stagnant air for the radiator to sit in. Similarly, when the Antec P183 V3 is in the horizontal orientation, the top case fan provides enough airflow to vent the hot air out of the system before enough hot air can congregate and cause a rise in temperatures.

Our very own company President Jon Bach was so intrigued by these results that he dusted off his college textbooks to try to come up with a mathematical reason for our results. This is his take on the physics involved:

Let's do a thought experiment to see what we would expect in terms of the bouyancy of hot air inside a chassis, and how that relates to the air pushed by a typical 120mm fan. We'll use an average room temperature of 20C (68F).  In our thermal testing, under load with maximum temperatures, we saw chassis panels around 40C average.  Let's round it up to 50C so we're sure to give convection the biggest advantage possible.  Heck, let's double the average air temperature difference measured, and use 60C.

Density of air at 20C: 1.2041 kg/m^3
Density of air at 60C:  1.067 kg/m^3
Bouyancy of 60C air in 20C air:  0.1371 kg/m^3

A P183 chassis is 0.04 cubic meters in internal volume.  Therefore, if you fill an Antec P183 chassis with 60C air, and surrounding air is 20C, the air inside the P183 would have a bouyancy equivalent to the weight of 5.484 grams.  That's about the weight of two pennies. How does that translate into air pressure across a top 120mm fan?  The column of air coming into play has an air volume of 0.00576 m^3, creating a bouyancy of .79 grams over the fan's area of 144 cm^2.  That translates to 0.0054861 grams/cm^2, or 0.54861 mmH20 (the standard unit of measurement for fan static pressure).

That's about half the pressure put out by our Antec TriCool fans on their lowest setting.  That means that even one of the lowest pressure, quietest fans that we sell, would *double* the pressure necessary to overcome the air pressure caused by convection, in the hottest scenario we can imagine.  And this was after doubling the average air temperature increases we actually measured.  When using a 40C average air temperature, an Antec TriCool fan on low setting has 4x the pressure necessary to overcome convection.  Given the results of this thought experiment, the results of our emperical testing are making a lot more sense.  Convection, while a strong concept in thought, simply does not generate the results necessary to play a discernible role in a typical chassis.

What our testing has shown is that the Silverstone FT02B-W has great cooling, but it is not due to the case being able to work with the forces of convection.  Instead, the benefit is due to the fact that the internal layout adds very little resistance between the intake and exhaust fans. In traditional cases, the front intake has to go past the hard drive mounts (and any drives installed in those mounts) before it reaches the motherboard and other hot components. While the distance is not huge, the extra 5-7 inches and blockage by any drives is enough to cause a drop in the amount of directed airflow the intake fans can provide. In the Silverstone FT02B-W, the intake is at the bottom of the case rather than the front, which allows the front intake to completely bypass the hard drive mounts (turning the 5-7 inches into only 1-2 inches). By having the intake fans at the bottom, it also allows for the use of multiple large fans (in this case 180mm fans). Normally there are power buttons, LEDS, brackets and many other things around the front intake that the fans have to work around. By moving the intake away from these obstacles, you can have a very large rectangular area in which to mount fans almost as large as the case is wide.

In conclusion, vertical oriented cases can cool very well, but don't expect a case with an vertical airflow to automatically have superior cooling to a traditional case. You need to take into consideration how restricted the airflow is and the size/location of the fans. In the Silverstone FT02B-W, moving to a vertical orientation allowed for Silverstone to use larger fans and achieve a much shorter run from the intake to the hot components resulting in a very well-cooling case, but not all case manufactures will spend the time to ensure this same level of cooling. According to our testing, the internal layout of a case is still the most important factor to case cooling and not the orientation of the airflow.



 
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Ben

Could you just test the same case normally, and then again rotated 90 degrees to see any impact on connection. you could, just for fun, rotate the case 90 dagrees Ge other way to see if forcing the air down makes any difference.

Ben

Posted on 2011-08-10 15:52:55

Ben, that's a very interesting idea.  We tested with a 90 degree rotation...why not a 180 degree rotation?  Vertical cooling vs anti-vertical cooling!  We may just have to try that.

Posted on 2011-08-10 16:05:53

Haha, I agree with Ben's idea. You should definitely try that one guys...

Posted on 2011-08-10 17:48:56
Mike Rudziensky

Just wanted to chime in and let you know these articles are awesome!

Posted on 2011-08-10 17:55:24
Bob Sadler

These tests have got me actually thinking about what you expected the results to be and what the results actually were.

The idea that the Vertical Case should do better with cooling relies upon the idea that hot air rises, and while this is true, if the hot air has no inflow of cooler air, it's not going to rise all that fast.  Hot air rises, albeit slowly, but put a fan at or near the bottom of your Vertical Case to draw the cool air in, then the hot air will be pushed out by the cool air rushing in.

When I thought about this with my own System, a Vertical System, I thought this was a no-brainer that the heat should just rise up and leave, and while that's exactly what will happen, if there's no air coming into the case, there's nothing to push the hot air up and out.  If anyone has ever been in a church on a 110 degree day, you know full well how this works, especially if the Church was built before the advent of Air-Conditioning.

I would like to see what results you would get if you added a fan at the bottom of the Vertical Case that would draw room temperature air into the case, which should then push the hot air up and out, at least up, closer to where the top fans are, which then pull it out.

Bob

Posted on 2011-08-10 21:29:07
EricGaray

Very similar results to my own test review of the silver model. The unrestricted airflow does more for the components than fan power. However, convection is still a very important principle to consider in all computer cases. In
vertical computer cases, it's extremely important that the design of the case create a bit
of a wind tunnel for optimal results. In other words, cool air should
get pulled in through the front, efficiently reach the
motherboard area cooling components and finally be expelled out of the top or back of the case.

A very good indicator of optimal airflow is AMD's retail CPU cooler. (I use a very hot and potentially loud AMD test system to measure thermal results as well as any noise blocking properties which have great value. No one likes an audible tin-can system.)

If too much air gets expelled out through the top of the case, the cool air coming in through the front will be drawn to the top of the case before the cool air gets to motherboard area. In this instance, the retail cooler got louder. The Antec DF-85 case is one such case that performed better with the top holes blocked off. Even with the case fans on high, the retail CPU cooler got quite loud. The rear fans did the proper job of creating the wind tunnel.

Another good example is what Puget Systems does to the Antec P183. You typically cover the top fan vent with sound dampening material because it creates a better wind tunnel and eliminates a little more noise. The secondary internal HDD bay mounted fan is very handy helping push the cool air to the back.

With that said, it's ultimately not the number of fans you have in the case, but how they are configured creating as much unrestricted the air flow as possible coming in from the front (as with the Antec P183 case) or the bottom (as with the Silverstone Fortress 2). 

Posted on 2011-08-11 04:23:59
Denis

Thank you for an excellent article. I have often wondered about the placement of intake fans in typical (horizontal) tower cases. In a normal case, air comes in from the lower front and out the upper back with the intention of passing over the main components (GPU, RAM, CPU). But first it has to get through the block of hard drives. And then it has to get past a long graphics card which usually divides a case into 2 areas and directs most of the airflow towards itself.

Perhaps it is time for horizontal cases to abandon some of the front 5.25" bays and put another intake fan in, purely to cool the CPU area of the motherboard. For example, in a typical row of 5 external drive bays, you could replace the middle 3 or upper 3 with a 120mm intake fan. Who says the DVD has to be in the top bay? And what are 5 external bays used for anyway? This would effectively create the same direction of unimpeded airflow that the Silverstone cases enjoy, but in a horizontal case.

Posted on 2011-08-11 13:49:54
EricGaray

Confirmed points there Denis. I would like to see a case that has configurable 5.25" and 3.5" bays. In other words, designed in a such a way I can remove 2 at a time versus the usual whole tray such as things are with the Antec P183 case. Case manufacturers have the ability to get innovative like this. They just need motivated.

Posted on 2011-08-11 19:06:03
taylorss

Great article!  Can you please also comment about the sound of the Silverstone case?  I know the article was on cooling, but I was curious about how quiet the Silverstone case is with the large fans.  From the reviews I have seen, it looks like it would be pretty quiet.  Also, any thoughts on the size of the case as compared to the Antec.

Posted on 2011-08-11 17:45:48

Silent PC does great reviews with an emphasis on noise levels, and they have a review up for the FT02 (empty case, no hardware).  You can see the noise results here: http://www.silentpcreview.com/...

Unfortunately, SilentPC hasn't reviewed the P183 case alone as far as I could find, but they have reviewed our Serenity PC's, which use the Antec P183 V3.  You can see those results here: http://www.silentpcreview.com/...

To summarize, the FT02 was 19-30dBA depending on fan speeds, and the Serenity was 11-12.5 dBa depending on system load.

Now, this is not a true comparison, since the Serenity had quieter fans installed, but that brings up another point that we didn't really touch on:  It is fairly easy to find quiet versions of 120mm fans since they are pretty much the industry standard today, but it is much harder to find quiet 180mm fans. 

To summarize, the FT02 is definitely louder than the P183 V3, but since we put a large emphasis on quiet operation, we are also much more picky than most other manufactures. 

Posted on 2011-08-11 20:08:48
Tony

SilentPC did test a RV02 (which is very similar to FT02) and has direct comparison chart showing how it compared to other cases including P183 when using a multi GPU setup:
http://www.silentpcreview.com/...

Please keep in mind that this SilentPC test was done before we upgraded RV02 and FT02 with the newer AP181 fans in 2010.  So the performance gap would widen even more if they are repeated again.

I am sure Puget could create an awesome setup with a FT02 that can be both cooler and possibly quieter than what they could do with the P183!  :-)

Posted on 2011-08-12 07:47:47
EricGaray

The Silverstone Fortress 2 is 19.5" tall x 8.3" wide x 24-1/4" long (deep). This is a really deep case and may not fit inside your lower desk cabinets. Make sure you have the cabinet depth if that's where it's going. The FT02 is 4" longer (deeper) to make room for those 3 x 180mm fans.

The Antec P183 V3 is 20.25" tall x 8.1" wide x 19.9" long (deep). It'll fit in your average cabinet. Don't forget to account for wiring.

Speaking of FT02 noise, the fans are rated to 27dB(A) max but that's based on measuring the stand alone fan. Inside the case, the fans are much quieter (about 17dB) measured from the side partially due to the sound dampening properties of the case. The window model lets just a little more noise out. However, the fans can be throttled back a bit more and the case will be very quiet.

It's also worth noting that any fan noise escapes the FT02 at the top of the chassis as it's the only vented area while any noise escapes the back of the P183 V3. If the FT02 is placed anywhere near floor level, you can hear a retail cooler from the top. If the P183 V3 is near a wall, you'll get the noise bouncing back a bit. I recommend a good aftermarket cooler like the Gelid, NZXT Havik, Noctua air coolers, or liquid Kuhler units to remove that possibility.

Hope this answers the question.

Posted on 2011-08-11 20:46:16
Guest

If you're going to do vertical cooling, add a chimney!  Adding a chimney increases the volume subjected to the bouyancy effects while leaving the horizontal surface area intact, which should increase the pressure involved.

Posted on 2011-10-09 02:02:59
Paul Uszak

I'm trying this right now. I'm doing some steampunking of a new pc and will be adding a chimney to the top of a mainly enclosed wooden case. The whole bottom of the case will be open, and I'm trying a first guess at chimney height of about 400mm.

Posted on 2014-11-17 04:02:03
Ben Wetherbee

More testing should be conducted here. 

Most mainstream horizontal cases actually concede that vertical dissipation is advantageous... the top exhaust. 

Take a case that does not have a top exhaust and run the same comparison.  I am willing to bet that it will cool better when flipped to a vertical position.  Also, there are a plethora of other factors that should be considered here.  A negative pressure horizontally-oriented case was tested against a positive pressure vertically-oriented case.  In regards to negative and positive... it will make an impact in regards to GPU cooling and also the design of the GPU's cooler.  Does the GPU cooler push air out the back of the case or does it blow air in BOTH directions (in and out).  This small test simply doesn't make a strong argument to which orientation actually performs better.

Posted on 2012-05-14 18:17:52
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