Rear case fans blowing INTO the case - good idea?

davidstone28 · Post by **davidstone28** » Mon Jun 28, 2004 1:15 pm

Is there any reason why I shouldn't reverse my rear case fan in my Sonata so that it blows air into the case?

Sure, it will mess up the supposed airflow, but I installed it the 'wrong' way round by accident and the CPU temps dropped by 5-6 degreesC. HDD temps stayed the same - a toasty 44 degreesC. System temps were similar.

rtsai · Post by **rtsai** » Mon Jun 28, 2004 1:34 pm

You'll probably end up with lots more dust (unless you install an air filter back there).

davidstone28 · Post by **davidstone28** » Mon Jun 28, 2004 2:38 pm

Apart from that, is there any other reason not to?

esn · Post by **esn** » Mon Jun 28, 2004 3:20 pm

davidstone28 wrote:Apart from that, is there any other reason not to?

In my home office setup I've got 2 towers sitting side-by-side. They are mere inches from a wall at the back and are surrounded by 11" deep bookcases on both sides (bookcase, tower, tower, bookcase with roughly 10" total side-to-side clearance). The major path for hot air to escape is up along the wall. Now, in this setup, if I reversed the case fan, I'm sure I'd intake some of the power supply exhaust back into the case.

Since you've seen a drop in temps, I'm assuming that you must have good ventilation at the back of your box. Now, if I were to build a couple power supply ducts, it might be worth a try.

Post by **NeilBlanchard** » Mon Jun 28, 2004 3:42 pm

Hello David:

You need better intake flow -- your hard drive(s) are probably even warmer with the rear fan reversed than they were with it the "right" way around...so look for the SPCR threads on modifying the Sonata's front bezel to free up the air flow down low on the front *past* the HD's and out through the rear fan. In theory this could help the CPU temps run where you are seeing them now *and* help your HD's run much cooler. Heat kills hard drives.

It is also possible that the PS fan will run slower with proper case ventilation -- with the fan reversed, you are forcing (most) of the hot air out through the PS.

As for more dust getting in -- this is a fallacy! If air is flowing through the case -- whether it is being pulled through or pushed through, then dust will be carried into the case. Air carries dust, and if air flows through the case, then dust will get into the case. Filters can reduce some of the dust, but they also will reduce the air flow some as well.

So your accidental reversal of the fan *was* useful, because it helps diagnose what is happening in your case. Almost evryone with the Sonata has found out this shortcoming -- let their experience be your guide.

Bluefront · Post by **Bluefront** » Mon Jun 28, 2004 6:24 pm

Really there's no one "best" way with fan direction.....it depends on the rest of your case configuration. I've built positive pressure cases (fans blowing in) that worked perfect.

As far as the dust thing....if you have all your fans blowing out (negative pressure) there is a real possibility dust will be pulled in through your optical drives. Not good. Filter the incoming air that a case fan is blowing in (positive pressure), and your case stays cleaner, and your optical drives stay cleaner.

Most people around here do not want the PSU fan to exhaust all the case air....it can speed up the PSU fan and increase noise. My #2 computer works like this w/o problems, no extra noise. It just depends....

mr_pickles · Post by **mr_pickles** » Mon Jun 28, 2004 8:37 pm

Well, here's my previous thread on the subject (and I'm sure mine wasn't the first):

http://forums.silentpcreview.com/viewto ... highlight=

It's worked out well for me. It brings in cooler air to my CPU heatsink and so I've been able to further undervolt both my front intakes and heatsink fan. My PSU hasn't revved up but I do have a blowhole fan exhausting air as well.

nutball · Post by **nutball** » Tue Jun 29, 2004 12:13 am

I tried this configuration at one point. It certainly reduced the CPU temperatures dramatically, at the expense of high HD and graphics card temps. This was with a bottom-feeder PSU IIRC, so lord only knows what the airflow pattern was!

I might try again when I've put my PSU/HDD duct in my case, though again, it's not intuitively obvious where the heat would go in such a configuration.

rperezlo · Post by **rperezlo** » Tue Jun 29, 2004 2:23 am

A 'different' idea I've been thinking about the last few days: What if you leave the top CD bay open and use it as a exhaust? In my case the air would enter through both 12 cm fans (front and rear), then go up and leave through the CD opening (maybe helped with a fan) and the PS exhaust.

I have a couple of good reasons to think this will work for me:

- I did reverse the rear fan once by mistake and it lowered my CPU temps and the noise. The noise (not a lot) that I normally hear comes mostly from the reflection of the 120 cm fan on the wall behind, so that blowing in instead of out reduces that noise. The front opening may increase the noise but I won't know how much until I try. The computer is not in my desk but in the floor, so that it may work.

- The only drawback was that the HD temperature increased by 4 or 5 C until it equaled the MB temperature. I think this has to do with the airflow inside the case, probably not enough air going out (well, too much impedance using your term), that's why I thought on opening the CD bay.

- My other element is a very quiet PS from BeQuiet that has the disadvantage of blowing a really tiny amount of hot air out of the case, so that it is not really working as a exhaust. Again, I think I need some reinforcements here and the CD bay would help.

What do you think? Will it work?

Maybe these really hot days we have in Madrid now (over 40 C every day for one week) are warming my brains in addition to my CPU...

glisoni · Post by **glisoni** » Tue Jun 29, 2004 4:27 am

rperezlo wrote:A 'different' idea I've been thinking about the last few days: What if you leave the top CD bay open and use it as a exhaust? In my case the air would enter through both 12 cm fans (front and rear), then go up and leave through the CD opening (maybe helped with a fan) and the PS exhaust.

I have a couple of good reasons to think this will work for me:

- I did reverse the rear fan once by mistake and it lowered my CPU temps and the noise. The noise (not a lot) that I normally hear comes mostly from the reflection of the 120 cm fan on the wall behind, so that blowing in instead of out reduces that noise. The front opening may increase the noise but I won't know how much until I try. The computer is not in my desk but in the floor, so that it may work.

- The only drawback was that the HD temperature increased by 4 or 5 C until it equaled the MB temperature. I think this has to do with the airflow inside the case, probably not enough air going out (well, too much impedance using your term), that's why I thought on opening the CD bay.

- My other element is a very quiet PS from BeQuiet that has the disadvantage of blowing a really tiny amount of hot air out of the case, so that it is not really working as a exhaust. Again, I think I need some reinforcements here and the CD bay would help.

What do you think? Will it work?

Maybe these really hot days we have in Madrid now (over 40 C every day for one week) are warming my brains in addition to my CPU...

Maybe a top exhaust? I saw a lot of cases with top exhaust fan. Since you have all the fans blowing in, hot air is moving up and natural place for it to go out would be area between PSU and front 5 1/4 block.

rperezlo · Post by **rperezlo** » Tue Jun 29, 2004 5:30 am

Yes, the idea and the airflow are the same that those of the top exhaust but without having to open new holes in the case. I really don't want to go through all the make-a-hole process (deinstall everything, drill new hole, clean, install everything). And if it doesn't work I always can revert back to where I was, something that is not possible with a new hole in your case.

Post by **Ralf Hutter** » Tue Jun 29, 2004 5:43 am

Try it. Monitor your temps using something like Motherboard Monitor. If it doesn't work, try something else. It just takes a few minutes to flip the fans over.

rperezlo · Post by **rperezlo** » Wed Jun 30, 2004 12:08 am

Here are the results (idle temps). Remember that I not only inverted the rear fan but also opened the top CD bay as an exhaust and placed a 8 cm fan blowing outwards in it.

- Before: CPU 53 C / MB 46 C / HDD 35 C
- After: CPU 47 C / MB 47 C / HDD 39 C

That's 6 C lower in the CPU and it's enough reason for me to leave it like that. I had stability problems when CPU temps reached 63 C and in a burn test yesterday the maximum load temperature was 56 C.

The noise is lower than before from the operator position and higher from the front of the computer. The reason is that the sound was previously going out from the back and bouncing in the wall, while now it is going out from the front into open space and a curtain, so that it doesn't reach me unless I put my head in front of the exhaust. In any case, it's low volume and low frequency with some air woosh, so that it is undisturbing for me.

For me these numbers show that the case has a serious intake problem in the front fan. This is probably due to its low speed (yes, and to the clearance of the input, but I don't want to cut anything), so that I'll get a rheobus and try again with its voltage a bit higher.

The case is one of those Antec SLK3700 clones without the front door (BTW, Ralf Hutter, that was an excellent review). It has a rear 12 cm fan blowing in @ 850 rpm, front 12 cm fan @ 600 rpm, CPU Artic Cooler with fan @ 1600 rpm, rear slot fan at 5 V and front exhaust fan at 5 V.

glisoni · Post by **glisoni** » Wed Jun 30, 2004 12:11 am

rperezlo wrote: I really don't want to go through all the make-a-hole process (deinstall everything, drill new hole, clean, install everything).

Yes, its a lot of work. What case do you have? On mine, top plate is mounted by screws, so it is easy removable. Maybe yours too? You my try to remove it and that fit a fan on a piece of cardboard and test. If its fine, then drill and cut, if not, put back the top plate, no harm done.

rperezlo · Post by **rperezlo** » Wed Jun 30, 2004 12:43 am

It's 'stitched'. As I said before, it is an Antec SLK3700 clone.

http://www.ibertronica.es/NuevaSonata.htm

davidstone28 · Post by **davidstone28** » Wed Jun 30, 2004 1:42 am

After some experimenting, here are my results of reversing the rear case fan to blow into the Sonata:-

(Equal CFM 120mm case fans)
Blow in:
CPU idle 50C load 57C, HDDs 44C
Blow out:
CPU idle 54C load 60C, HDDs 42C

I could only get those results when the rear case fan and the case fan next to the drive cage blew the same CFM.

When I swapped in a more powerful rear case fan, that blew more air, the temps changed to the following:-

(Unequal CFM 120mm case fans - rear fan more powerful than HDD drive cage fan)
Blow in:
CPU idle 46C load 52C, HDDs 54C (no that's not a typo!)
Blow out:
CPU idle 54C load 60C, HDDs 42C

So to conclude:-

1. I have decided to leave everything as it was originally ie rear case fan blowing outwards, since a 2C saving on HDD temps is more important to me than 5C on the CPU

2. The airflow around the Sonata's HDDs really does suck!

3. The Nexus 120mm fan doesn't pump much air, even at 12v.

Bluefront · Post by **Bluefront** » Wed Jun 30, 2004 5:20 am

Heh...at 12v your Nexus blows a lot of air, either in or out. What happens to the airflow in your case is another matter. If your 120mm case fan is blowing in, and another low powered fan is blowing in on the hard drives, it is quite possible the pressure from the 120mm is restricting the airflow over the hard drives. Why don't you try blowing the rear fan in and the front fan out? Hard drive temps may improve, at the same time keeping the CPU temps lower.

Airflow is a difficult subject because of so many variables....but if you keep working at it,you might be successful. (Sonata cases...Baaa)

markjia · Post by **markjia** » Wed Jun 30, 2004 8:44 am

What if you tried moving the HD to the rear of the case, under the PCI cards? I know mounting it here would be a little difficult, but it should be possible (I've seen people do similar things). This way, you won't have the fan blowing hot air towards the drive.

davidstone28 · Post by **davidstone28** » Wed Jun 30, 2004 9:14 am

Bluefront wrote:Heh...at 12v your Nexus blows a lot of air, either in or out.
(Sonata cases...Baaa)

Actually, the Nexus doesn't blow much air, even at 12v - its the stock Antec that pumps more. I definitely agree with your second statement though

msm_zgok · Post by **msm_zgok** » Wed Jun 30, 2004 11:47 pm

Intake or exhaust rear fan had no effect on my CPU temps.

As for mounting HDDs in the rear- would the temps rise because it sits directly beneath a video card?

Rear case fans blowing INTO the case - good idea?

Rear case fans blowing INTO the case - good idea?

You need better intake flow!