Question about positive air pressure...

oldestgregg · 16 Nov 2017 at 01:37

In my 780t Corsair case, I have two of the 140mm Corsair magnetic fans in the front in a pull configuration and two of the same fans on the roof,also set to pull ,connected to my H110i GTX. I have a single 120mm Corsair fan set to pull on the rear of the case as well but its not the same as the other four fans I am using. Would I be correct i thinking it would be just as effective to only use the two at the front and the two on top and do away with the one at the rear? My thinking is that its pulling air in the front and up through the rad and out the top of the case and that the single fan on the rear is disrupting the flow that those four fans create?

Glanza · 16 Nov 2017 at 08:40

Minimal difference, I like to keep a fan at the rear for exhaust.

doyll · 16 Nov 2017 at 13:06

2x front intakes, 2x top intakes and 1x rear exhaust?
or
2x front intakes, 2x top exhaust and 1x rear exhaust?

I would have 2x front intakes, 2x top intakes, 1x rear exhaust and remove all unused PCie back slot covers so there is front to back airflow around GPU, all fans speed controlled by component temp .. top and back on CPU temp control and front intakes on GPU temp control.

Gtiracer · 16 Nov 2017 at 14:58

Well, heat rises, so having the top as an exhaust seems like natural progression for me, that's how i've always set my fans up personally

doyll · 16 Nov 2017 at 15:49

No, heat does not rise. Heat radiates. When air expands and becomes lighter it will rise above cooler air, but this only happens when nothing else is distrubing the airflow .. like fans do. A fan even a extremely low speed easily overcomes any warmer air rises concept.

If your top fans on radiator are intakes then they are pushing air down toward GPU.
If they are exhaust they are using the already heated air coming off of GPU.
Doesn't it seem more logical to use the front fans to move cool air to GPU, then on back and out of case through open PCIe slots?
This front to back flow with PCIe back slots open has been proven to lower GPU temps significantly .. and CPU temps with air coolers too.

Most tower cases are still not designed to properly flow air from front to back and thereby supply cool air to both CPU and GPU coolers. That is why many of us remove the PCIe back slot covers to improve rear ven area and improve front to back airflow.

Pocah · 17 Nov 2017 at 00:11

The general rule is "Diminishing returns" ~ the more fans you have, the less effective adding another. But, I think in your situation, where you have all the fans drawing air in, the I wonder where is it getting out? Pressure is one thing, flow is another, and I think while you have tons of pressure you may be missing out on flow. I would certainly try removing that rear fan. At best I don't think it's helping much ( diminishing returns ), at worst you are actually increasing pressure too much at the expense of flow and so removing that fan may well increase the flow out of the case, which will help a lot.

Gtiracer · 17 Nov 2017 at 00:18

Well, Ill bow to your greater knowledge. I was under the impression, you were a little pedantic regarding the heat and hot air difference, because air will be coming into the system and once inside the machine it becomes hot air so I thought that would be self explanatory. With all the Hot air moving inside the case I presumed Thermals would take effect and naturally the colder air would gravitate to the floor.

tres_kun · 17 Nov 2017 at 05:22

My advice
Overall you want to have positive preshure in the case
The 2 in the front as intake
The 2 on the top as exost
But because you have a liquid cooler fitted it will reduce airflow resulting in positive preshure in the case
If you want more airflow you can fit a fan on the bothem as intake and a fan on the back as exost
Your description for your fan orientation in confusing

I hope that you haven't set all as intake
You need an exost to have airflow
Think about a car engine what comes in has to come out to function

Pocah · 17 Nov 2017 at 09:13

Gtiracer said:
Well, Ill bow to your greater knowledge. I was under the impression, you were a little pedantic regarding the heat and hot air difference, because air will be coming into the system and once inside the machine it becomes hot air so I thought that would be self explanatory. With all the Hot air moving inside the case I presumed Thermals would take effect and naturally the colder air would gravitate to the floor.

Don't bow, he was just as wrong as you were!

If "heat rises" is wrong then so is "heat radiates". It's true to say that heat does not rise, hot air rises but then heat does not radiate, matter absorbs and emits electromagnetic radiation. Conduction and radiation are processes by which heat is transferred, not heat itself. But honestly most people say heat rises so in my mind that just fine. It's not exact, but we get the idea. Well, most of us do.

And in fact heat removal in a PC is by conduction not emission.

doyll · 17 Nov 2017 at 12:33

Gtiracer said:
Well, Ill bow to your greater knowledge. I was under the impression, you were a little pedantic regarding the heat and hot air difference, because air will be coming into the system and once inside the machine it becomes hot air so I thought that would be self explanatory. With all the Hot air moving inside the case I presumed Thermals would take effect and naturally the colder air would gravitate to the floor.

Test it out yourself and you will find that heated air / hot air make no thermals because even a slow moving fan will overpower a thermal airflow. so if most people told you the earth was flat and the center of the universe you would believe them? Maybe you would but I won't.

What tres_kun said.
Air flows the same way water or any other fluid flows. so the maximum flow of air through a case is the less of the two potentials; intake or exhaust. If a case as a maximum intake flow potential of 300cfm and and maximum exhuast flow potential of 100cfm the case has a mxium flow rate potential of 100cfm. The case will not flow more air in then it can flow out.

Experiment and see which works best top exhaust or top intake. I doubt you will find much if any difference if all PCIe slot covers are removed.

But if top is exhaust and PCIe slot covers are removed then their vent area is as likely to be intake as exhaust. Especially if GPU fans are running at higher rpm rates.

Pocah said:
Don't bow, he was just as wrong as you were! If "heat rises" is wrong then so is "heat radiates". It's true to say that heat does not rise, hot air rises but then heat does not radiate, matter absorbs and emits electromagnetic radiation. Conduction and radiation are processes by which heat is transferred, not heat itself. But honestly most people say heat rises so in my mind that just fine. It's not exact, but we get the idea. Well, most of us do. And in fact heat removal in a PC is by conduction not emission.

My use of the word 'radiates' may be different from yours. The way I was applying 'heat radiates' as being hotter object (heat sink / cooler fins) radiating heat and the cooler air flowing past them absorbing it.

The point was heated air does not rise in our computer applications where fans are being used .. heat is not causing any air to rise because ss I said, even a very slow spinning fan will created more air movement and overpower any heated air that would rise with now fans involved. And in order to get the heat from components that is transferred into the air in our cases out, we have to have airflow through our cases.

mattyfez · 17 Nov 2017 at 22:37

I've tried various fan configurations over the years and my general view is it doesn't make a right lot of difference.

I do have a big case though, the only case fan I currently run is the rear exhaust and a passive top vent. I have about another 4 fans disconnected as they just make additional noise noise and don't really affect cpu and gpu temperature.

Small cases though might be different, you'll just have to test for yourself.

Edit: I've only ever used air cooling, not WC.
A good quality cpu fan/cooler makes the biggest difference assuming you don't have a tiny case.

ToTheMax · 18 Nov 2017 at 15:51

I've got a 780T running 7 corsair ML140's, front intake (x2) rear (x1) and 280 AIO with push pull on the roof. With a 1080TI dumping heat into the case I can feel noticeably warm air being exhausted from the top & rear so in my case that rear exhaust is needed imo. I've been running this for quite some time now and dust doesn't seem to be a problem, I wouldn't get too obsessed about having a positive pressure imo
.

Mercutio · 28 Nov 2017 at 02:50

I went custom. (w)600 x (h)300 x (d)400 "box".
1 x 200mm intake on each "side" (2x200mm total).
2x 240mm rads, push/pull on the rear for exhaust. (4x120mm total)

Good overclock on everything below, nothing breaches 55c under load