Temperature *worse* with intake fan??!

[fendel]

This is weird.

I built a system in an Antec 3700BQE case with a 120mm exhaust fan in the back. Nice and quiet. CPU runs about 30C idle, 42C under load. But I have three 7200rpm hard drives in the internal 3.5" bays and was concerned about their temperature, so I tried an intake fan.

First off - with no intake fan, my drives are running at 36C, 33C, and 30C. I added a 120mm Vantec Stealth -- this case has a spot for it, decent air intake through the bezel as far as I can tell. The temps on the drives in the 3.5" bays actually went up 2 to 8 degrees Celsius. I know, you're thinking I've got the fan turned the wrong way, but that's with the fan blowing in the right direction -- because when I had it backwards it was even worse!

How can an intake fan actually increase temperatures? (Room temperature is about 21C.)

 

[Gamingphreek]

Unless you are experiencing stability problems i wouldn't worry about HD cooling. However it seems that somehow the pressure is not at the happy equilibrium inside your case. Is your case on the ground?

-Kevin

 

[Gravity]

Is your psu sucking air to the top of the case? Perhaps some cardboard would block it from the rest of the case smoothing your airflow.

What kind of case are you using?

 

[dc5]

possibly too much possitve pressure. meaning, warm air is building up inside your case, and the exhaust fan isn't spinning fast enough to release the air. you can try increasing the exhaust fan speed and decreasing the intake fan speed.

 

[fendel]

Hmm. No stability problems. I guess I just want to maximize HDD life, although that's kind of funny considering I'll probably be replacing the lot with 300GB drives when those are fifty bucks by Christmas.

Case is on the ground, and it's an Antec 3700BQE midtower. I'll have to check on the PSU's effect on airflow... PSU is exhausting warm air, case exhaust fan is exhausting cool air, don't know what that means in practical terms...

Temps are now up 2-5C from what I said earlier. Wish I had taken better notes when I had the fan installed, because it feels like guesswork...

 

[Mucker]

According to Antecs site, the included rear fan on the 3700 BQE turns at 1200 rpm (38cfm). Your Vantec turns 1500rpm (54cfm). I would be inclined to swap the fans as to create a negative pressure situation. Contrary to popular belief, I've seen much better cooling results using this arrangement.

I noticed that when I replaced the stock rear fan on my Super Lanboy (1200rpm) with a higher speed fan (a Tt 120mm 2000rpm) the CPU temp dropped 2C with all fans running at the minimum fan controller voltage. True that the Tt was spinning faster at comparative minimum speed, but the cooling was better.

It could be that you'll see a similiar result with a swap.

m

 

[Tiamat]

Also, Harddrives dont need much airflow around them to cool effectively, as long as there IS airflow. If you are a stickler for quiet as I, Perhaps try to rig an 80mm panaflo to blow on your harddrive. Or, just not have an intake fan, and monitor the temp of your hdd. If your hdd is at a safe temp, might as well not put the intake fan in.

 

[JBDan]

Originally posted by: dc5
possibly too much possitve pressure. meaning, warm air is building up inside your case, and the exhaust fan isn't spinning fast enough to release the air. you can try increasing the exhaust fan speed and decreasing the intake fan speed.

Too much +pressure IS the issue and you must speed up your exhaust to match or exceed the intake to get proper cooling. Get a faster exhaust or better yet, slow down the intake.

 

[fendel]

D'oh! I was assuming all 120mm fans are alike...

I forgot to mention this before, but while waiting for the 120mm fan to arrive from Newegg, I had rigged up a 92mm intake fan (a Vantec Stealth I had lying around). Since I wasn't expecting any surprises, I was monitoring my temperatures only sporadically and not writing them down, so I don't really remember what the results were. But I think they were lower temps than I got with the 120mm...

The 92mm fan is 28cfm. I think I will try it tonight. With the intake at 28cfm and the exhaust at 38cfm (thx Mucker, I can't believe I didn't think to look that up on Antec's site) is a negative pressure like that OK? I'm guessing it's better than no intake fan, but I'm a little clueless about this (as you can see ).

 

[Nessism]

120mm fans have a large center hub and there's a dead air spot directly behind the hub. For this reason, spot cooling with a 120 may not be as effective as it would be with a smaller fan. Another thing that could be causing a problem is the airflow path inside the case. Sometimes a push-pull fan setup like your two 120 arrangement can create localized hot spots inside the case.

You might want to rerun your temp tests again, this time taking careful notes. Your temp increases seem above what one would expect due to localized hot spotting and/or a dead air spot directly behind a fan.

Good luck.

Ed

 

[fendel]

Installed the 92mm fan this morning and left the PC running all day... currently the HDs are running at 38C, 32C, and 30C -- worse than my initial reading with no intake fan but better than my reading with no intake fan after running for a while....

I may have to just live with those numbers... I don't want to replace the rear fan or move it because it's attached with these nifty rubber grommets that I would have to cut to remove it. Guess I'll keep an eye on it for now. I'm figuring it would help if I get rid of one of the HDs--I hate having three drives stacked up in the internal bays like that (there is space between two of them, but the third is right on top of another drive) but I can't fit a HD with adapter rails in the 5.25" bays. Too tight.

Thanks for all your comments!

 

[Mucker]

You don't have to ruin the grommets. Use a jewelers screwdriver and work them back through the holes. I have done it both with the clipped and unclipped grommets. If you are careful you can use these many times.

Antec will send you spares (like they did for me) if you ask nicely
You can get more here but shipping is outrageous: http://www.antec.com/us/productDetails.php?ProdID=30030

I think swapping your 120's would work well but that's just MO.

m

 

[VirtualLarry]

Originally posted by: JBDan
Too much +pressure IS the issue and you must speed up your exhaust to match or exceed the intake to get proper cooling. Get a faster exhaust or better yet, slow down the intake.

Interestingly, I've often seen positive pressure referred to as a good thing inside cases, as a sort of dust-collection prevention step. But I don't buy it, whether there is positive or negative pressure inside the case, the dust from outside will get pulled in and through, no matter what, unless you have some intake filters, IMHO. I agree that trying to have matched intake + exhaust airflow is probably the best in terms of efficiency of moving air.

 

[fireontheway]

Originally posted by: Mucker
According to Antecs site, the included rear fan on the 3700 BQE turns at 1200 rpm (38cfm). Your Vantec turns 1500rpm (54cfm). I would be inclined to swap the fans as to create a negative pressure situation. Contrary to popular belief, I've seen much better cooling results using this arrangement.

I noticed that when I replaced the stock rear fan on my Super Lanboy (1200rpm) with a higher speed fan (a Tt 120mm 2000rpm) the CPU temp dropped 2C with all fans running at the minimum fan controller voltage. True that the Tt was spinning faster at comparative minimum speed, but the cooling was better.

It could be that you'll see a similiar result with a swap.

m

 

[Mrvile]

Try placing the Stealth in the back, the stock fan up front. Also, what Nessism says is very viable. Try placing the drives at the top above the fan (since all the air blows to the sides and not to the middle) or at the bottom below the fan.

 

[fendel]

Currently my HDs are running at 37C, 30C, and 27C after being on overnight... I'm thinking maybe I will just keep an eye on it and leave well enough alone for now, and try switching the fans if the temps get too high... So far the highest temperature I've seen has been maybe 42C after a lot of disk activity, so I'm probably in OK shape with this. Thanks for all the good suggestions, I'm learning a lot from this thread.