Well, after yesterday's huge amount of RAC (621 TOTAL from 8am 11/4 - 9am 11/5, vs. my normal 90-100,000), I had the opportunity to conduct an experiment on my H100's airflow direction (2 fans only).

Here's the setup: a HAF 932 case with 2 GTX 780s, the radiator mounted at the top, using 2 Corsair Air Series SP120 fans. All the other fans are stock, as supplied by the manufacturer (one front 200mm blowing in, one side 200mm blowing in and one rear 140mm, blowing out. Running 3 WUs/780.

Before the outage, I had the radiator fans drawing air down into the case (to use the cooler air outside for "better" CPU cooling. The 780s were running at 64 and 71C, respectively. I reversed the fans (blowing warmer case air through the radiator) and found the temps of the cards are now 59 and 64C, respectively, not what I expected. And I don't see any change in CPU temp.

I would have thought bringing more cool air into the case would have helped cool the cards, but not so. Lesson learned: experimental evidence is better than trying to think things through. The science is settled.

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The air moving out of the radiator will, in almost every situation, be warmer than the incoming air. So you were blowing the hot air from the radiator down into the case. Rather then expelling it.
Unless you remove the hot air quickly it will always lead to increased temperatures inside the case.

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I have the same set up, I draw the air out of the case thru the radiator. I figured out long ago that it keep the temp inside the case cooler. I also reversed the direction of the 140 exhaust from from the back of the case so now it blows cooler air into the case under the radiator but over the top of the GPUs. That seem to also lower a little bit of the temps.

Zalster

I have the same set up, I draw the air out of the case thru the radiator(1). I figured out long ago that it keep the temp inside the case cooler. I also reversed the direction of the 140 exhaust from from the back of the case so now it blows cooler air into the case under the radiator but over the top of the GPUs(2). That seem to also lower a little bit of the temps.

Zalster

(1) That's how I had it originally set up, but I read a couple of articles that said it's better to run outside air through the radiator than inside air. Clearly, they were wrong, or didn't consider the case of hard gaming or SETI-like GPU usage.

(2)I'll give that one a try next time I mess around with the case. Can't hurt to have it even cooler.

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My radiators are several feet from the tower, and the fans pull air though them instead of pushing it. The fans themselves generate heat, and when they are pulling air, that heat is not introduced into the radiators. It is a good idea to use the coolest air possible to pull though a radiator, but I can see that may be difficult if the radiator is in or on the tower.

Steve

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My radiators are several feet from the tower

I understand that DIY liquid cooling systems are better, but I'm chicken - and I don't have the room right now anyway.

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The 780s were running at 64 and 71C, respectively.

Are you using the default fan profile? What's your room temperature? Who manufactured the 780's? I have a similar setup, 2x780, i7 4770k with h100i. I had to increase the fans profile to 80% so I can maintain 74 on the upper GPU when running 3 WU's.

Running Einstein, 61 upper 53 lower. Running 1 AP is also below 70's.

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(1) That's how I had it originally set up, but I read a couple of articles that said it's better to run outside air through the radiator than inside air. Clearly, they were wrong, or didn't consider the case of hard gaming or SETI-like GPU usage.

No, they are correct.
Using cooler air will increase the ability to remove heat from the GPU.
However, blowing it back in to the case makes no sense as you are just blowing the heat back in to the case, to use the cooler to remove it, to blow it back in to the case, to use the cooler to remove it, to blow it back in to the case etc, etc, etc...

As SciManStev has done the idea is to mount the radiator externally, so it is drawing in cooler air from outside of the case, and it is expelling it outside of the case as well.

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Grant
Darwin NT

The 780s were running at 64 and 71C, respectively.

Are you using the default fan profile? What's your room temperature? Who manufactured the 780's? I have a similar setup, 2x780, i7 4770k with h100i. I had to increase the fans profile to 80% so I can maintain 74 on the upper GPU when running 3 WU's.

Running Einstein, 61 upper 53 lower. Running 1 AP is also below 70's.

They're ASUS Poseidons, and I use EVGA Precision to boost the fans. The fans run at about the same % as the temperature in my setup. Room temp is around 67F. (I don't use the liquid cooling feature of the cards ).

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