fan - Does running a computer with the case open mess with the airflow/cooling?

My friends say that it should actually improve the cooling since there is more air available to it, especially the CPU fan. I have to admit that it at least looks like it would stay cooler.

I disagree. It should prevent the case fans from effectively running fast-moving air across the components, right? As for the CPU fan, the air around it isn't being refreshed as much with the case open, I think, so it's getting hotter, so the CPU cooling isn't as effective. Not that it would kill the computer, but it seems to me that it would make the cooling less efficient.

Who's right? This is about settling an argument, not trying to solve a real problem. The computer in question is a custom-made "1337 gaming b0x0r r!g" (you know the type) school computer with like 8 fans that's being used right now to make graphene using a LightScribe DVD burner (not a heavy task), and its case is open. The key here is that it has a good-quality case, and we can't try heat tests on it.

You are right, running the computer with the chassis side open wide is worse than having it closed (assuming the closed chassis has proper air flow).

Air flow is important, and if you just open the side of the case, the air stops flowing from front to back (the usual direction anyway), and instead lots of hot air just hangs over the components due to the lack of air actually moving.

Worry less about the CPU or anything with a fan on it, and more about the stuff that's passively cooled, as passive cooling depends on the air moving through the case, pulling the hot air away.

Perhaps think of it like this: Put a computer fan at the end of a 4 foot long, 3" tube and stick your hand near the other end. You can feel the air moving quite well, I'd bet.

Now take the same fan and just sit it on the table in a room. Stick you hand 4 feet away from it, you should notice that there's a lot less, or no, air pressure against your hand.

You may want to take a look a the answers/links in this SU question: Optimal Fan Placement and Direction for Air-Cooling a Computer

In theory, so some have said.

In practice, i've had a P4 running for maybe almost 10 years+, side off the case. Not in a data centre with perforated flooring, just in a house.

What Mel mentions re a data centre with perforated flooring, vs not, that's interesting, and makes sense. Matches my experience with the P4.

With what techie mentions, well, that also makes sense but I haven't had a problem doing it.. You could test it somewhat. This isn't generally recommended because there's a risk of static damaging a component once in a blue moon(and perhaps if it's badly built), but a person could put their finger on the heatsink of something that is passively cooled and see how hot it is, and compare with side on(momentarily taking it off to check), and with side off for a long duration. No doubt lots of technical people leave the sides off their computers for quick access to the insides.

If you are not in a data center environment, it really should not matter. As a matter of fact, opening the case might help you a little, unless of course, you have an air flow optimized rig like some gaming special systems do.

On the other hand, if your question is about a server in a data center environment with forced cooling, it absolutely matters and running it open case, make the matter worse, because, the perforated floor tiles on data centers, are located at those positions for a purpose. they push cold air from one side of the cabinet and pull hot air from the other side. And if your case is open, the heat rises in the cabinet vertically, instead of being pushed out to be sucked by the hot air collector side of the cooling system.

Why don't you measure for yourself? Arguably, the most important temperature is the CPU temperature which all modern CPUs provide a sensor which can be read. This is highly operating system dependent though.

On Linux, you can use the acpi command: acpi -t to display temperature information. If that is not installed (or connected), here are some more things you can try:

$ cat /sys/devices/virtual/thermal/thermal_zone*/temp  (Fedora 16/kernel 3.6)
40000
39000

Or on some kernels; $ cat /sys/devices/virtual/thermal/* (Ubuntu 12/kernel 3.10)

Or maybe

$ cat /proc/cpuinfo
processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 44
model name  : Intel(R) Xeon(R) CPU           X5690  @ 3.47GHz
stepping    : 2
microcode   : 0x10
cpu MHz     : 3457.977
cache size  : 12288 KB
physical id : 0
siblings    : 6
core id     : 0
cpu cores   : 6
apicid      : 0
initial apicid  : 0
fpu     : yes
fpu_exception   : yes
cpuid level : 11
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm ida arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips    : 6915.95
clflush size    : 64
cache_alignment : 64
address sizes   : 40 bits physical, 48 bits virtual
power management:

processor   : 1
... (for 11 more cores)

This shows that CPU0 is at 40 °C and CPU1 is at 39 °C. With that kind of information you can rearrange the case covers and see which arrangement is coolest.

On Windows, I remember finding a way. I would search in the System Information applet. Or maybe you have to install something.

I would expect the case cover on to provide the best cooling.