Push or Pull configuration

Hey all,
I am looking for some opinions about the configuration of my fans in a push or pull setup in a two loop system. I have read that fans in a pull setup make less noise over pushing. I will have a triple rad in the front case panel and a quad in the rear case panel so the air will travel straight through the case from the intake in the front to the exhaust in the rear. I will also have 4 80mm fans exausting through the top panel. Really my question is should I pull from the front and push from the back or have both rads pulling or pushing? The picture shows how I was going to set up my case but as you can see the rear rad is a triple, I will be using a quad in the rear.Thanks for all of your help so far getting me set up with everything.

Your rad is a source of airflow resistance, if you blow air onto the rad that creates a bit of positive pressure between the rad and fan where if you are pulling air through the rad it creates a bit of negative pressure between the rad and fan.

Since the fans look like they are directly mounted on the rads (like most setups are) I would have to say (based upon my own experience) that there is negligible performance/noise difference between push and pull configuration, though for some unjustified reason I prefer push over pull. I also enjoy falling asleep next to very loud 5000RPM 120mm fans so I can completely tune out practically any noise up to vacuum cleaner level so maybe i'm not the best person to ask :/ The way I see it, the fan can push a certain amount of air and the rad has a certain level of resistance to airflow weather the fan is behind or in front of it. Based upon the pattern of the fins on the rad and other physical parameters, there might be a bit more turbulence generated by either blowing into the rad or sucking air through it but in my personal experience it's not enough for me to notice.

Push-Pull, Blow-Suck, this topic has been debated thoroughly throughout the life of the forums and the topic comes up every now and then and there are some good arguments for either setup but most topics involve air cooling and case pressure. You might find some answeres searching through some of those threads while you wait on someone to chime in who has a bit more sensitive ears.

try em both outside the case and listen to htem to see which you like. performance wont be different enough usually to worry about anything compared to sound profile

A good balance of airflow is the important thing. Too much positive or negative will adversely effect fan performance. I'm not sure how you've got 4x120mm fans on the back panel (at least where they can effect your case airflow) but assuming that's true I'd go for
> 7x120mm IN and 4x80mm + PSU + HDD OUT (~ +3x120mm). That's a lot of positive pressure but I prefer that to any appreciable amount of negative pressure. There's also the plus that all rad air is fresh air.

> 3x120mm IN and 4x120mm + 4x80mm + PSU + HDD OUT is a lot of negative pressure (~ -5x120mm).
> 4x120mm IN and 3x120mm + 4x80mm + PSU + HDD OUT is also a lot of negative pressure, though not quite as much (~ -3x120mm).
Either way it's not a good situation, IMO.


You'll need that vent in any scenario but like I said, I've always been a proponent of positive pressure so that's my vote ...

QuietIce said:

A good balance of airflow is the important thing. Too much positive or negative will adversely effect fan performance. I'm not sure how you've got 4x120mm fans on the back panel (at least where they can effect your case airflow) but assuming that's true I'd go for
> 7x120mm IN and 4x80mm + PSU + HDD OUT (~ +3x120mm). That's a lot of positive pressure but I prefer that to any appreciable amount of negative pressure. There's also the plus that all rad air is fresh air.

> 3x120mm IN and 4x120mm + 4x80mm + PSU + HDD OUT is a lot of negative pressure (~ -5x120mm).
> 4x120mm IN and 3x120mm + 4x80mm + PSU + HDD OUT is also a lot of negative pressure, though not quite as much (~ -3x120mm).
Either way it's not a good situation, IMO.


You'll need that vent in any scenario but like I said, I've always been a proponent of positive pressure so that's my vote ...

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You make a good point, what I didn't tell you was that in the front panel of my case below the 3x120 rad is another set of 3x120 open holes to bring in ambient air. This also brings up another question. The radiators that I am using have 8 fins per inch. I was planning on using a medium speed fan rated at 70.5 CFM@1650 rpms. The 4 exhaust fans in the top panel are 80mm and run at 1500 rpm's moving 21.5 CFM of air. I am hoping that I have positive pressure with the additional 3x120's in the front panel. Plus I also have an extra 120 open hole in the back panel. What I wanted to do was keep the air coming into the front of the case and exit the rear and through the top panel.
Thanks for you input and I am open for more suggestions. Do you have more ideas now that I have told you how many fans I actually have which is 15.

If you've got six 70 CFM fans in front (did I read that right?) and your 80's are only 20 CFM then, ya', I'd say have all six in front IN with the four in back OUT. That should actually balance pretty well even adding in the PSU fan, which is usually low-CFM too ...

QuietIce said:

If you've got six 70 CFM fans in front (did I read that right?) and your 80's are only 20 CFM then, ya', I'd say have all six in front IN with the four in back OUT. That should actually balance pretty well even adding in the PSU fan, which is usually low-CFM too ...

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Yes, there are six 70 CFM in the front. Okay well thanks for your help, I appreciate it.

thorilan said:

try em both outside the case and listen to htem to see which you like. performance wont be different enough usually to worry about anything compared to sound profile

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Thanks for your advice, I will do this and pick the quietest config.

http://martin.skinneelabs.com/Radiator-Fan-Orientation-And-Shroud-Testing-Review.html

Push Vs Pull - This depends on fan speed/power. The high speed fans at 2000RPM with a 38mm fan thickness provided the best performance in a push condition. The slow speed fans with 1350RPM with a 25mm fan thickness provided the best performance in a pull condition. I would estimate that performance line is likely to cross in the 1500-1700RPM range where they are equal. So.... slow speed = pull, high speed = push, medium speed = it doesn't really matter.

2 fans Push/Pull vs others - It was very clear that when using two fans per radiator section, that the radiator intself acts as a flow spreader and provided great benefit to straightening out the air for the second fan in a push/pull configuration. Just like doubling up with a pump, there is a pressure benefit to doubling up on fans and this translates to about a 20-30% performance gain. The added fan pressure simply means and added gain in air flow and corresponding performance. None of the experimental pull/pull or push/push configurations provided any noteworthy benefit as it seams the air is simply too disturbed from the first fan to allow the second to perform properly when air is moving. I would always recommend a push/pull configuration for two fans and add a shroud to both sides if space allows.

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I would say that the things that help alot is to use Shrouds. Push or pull is similar but adding shroud help alot for less noise and more performance.

Im Pulling with 50mm shroud and it VERY silent and effective.

Spawn-Inc said:

http://martin.skinneelabs.com/Radiator-Fan-Orientation-And-Shroud-Testing-Review.html

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Thanks for the link, the review answered a lot of questions for me.

Boulard83 said:

I would say that the things that help alot is to use Shrouds. Push or pull is similar but adding shroud help alot for less noise and more performance.
Im Pulling with 50mm shroud and it VERY silent and effective.

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The article above does a nice comparison between the different configurations. Thanks for your input, I need to play around with different config's and see which works best.

NP ! skinee is the best

QuietIce said:

If you've got six 70 CFM fans in front (did I read that right?) and your 80's are only 20 CFM then, ya', I'd say have all six in front IN with the four in back OUT. That should actually balance pretty well even adding in the PSU fan, which is usually low-CFM too ...

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Is there a calculated amount of postive pressure within a case that would be considered the norm, and if so would it be measured using CFM? You've got me wondering how much positive pressure I should be looking for in my build

I suggest push in the front and pull in the back. I found this to be the best configuration, lowering the temps by 10c or more over the other configurations. When things start getting dusty, you can end up with 10c more for a total of 20c which is not good.

This configuration all makes more sense if you have a PSU in the standard spot, since PSU's are generally pulling from inside the case anyways. Pushing from the back would mostly get that air sucked into the PSU exhaust before it has a chance to flow over other components. Plus this way, your PSU helps the strength and coverage of your pull and keeps it all streamlined so you don't end up with 'dead areas' where air doesn't flow and builds up heat.

starrant said:

Is there a calculated amount of postive pressure within a case that would be considered the norm, and if so would it be measured using CFM? You've got me wondering how much positive pressure I should be looking for in my build

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You should be looking for the smallest amount of pressure possible and I'm sorry if my earlier post mislead you on that.

What goes in must come out - and vice versa, so CFM is the most common reference. The "perfect" set-up would have an exact balance of fans IN and OUT but, of course, that's impossible - there will always be a slight variance. I prefer to have just a little positive pressure because it's easier to trap dust as it's coming in at the fans. With negative pressure you've got a lot of little places around your case and components where air (and dust) is getting sucked into the case. I'd rather clean 2-3 specific places (well, 6 for your set-up ) than have to go all over the case with a cloth or hand-vac cleaning every little crack. Been there, done that, don't wanna' go back.

But that's just me. Some people prefer negative pressure (and I still don't understand why) and either way you go it's still better to keep it well balanced. Every fan is negatively effected by pressure whether it's outgoing fans straining for lack of air or incoming fans trying to push against the pressure. To keep a good flow of air you need a good balance of CFM IN and OUT because that maximizes your fan's performance, which in turn maximizes the airflow in the case ...

QuietIce said:

You should be looking for the smallest amount of pressure possible and I'm sorry if my earlier post mislead you on that.

What goes in must come out - and vice versa, so CFM is the most common reference. The "perfect" set-up would have an exact balance of fans IN and OUT but, of course, that's impossible - there will always be a slight variance. I prefer to have just a little positive pressure because it's easier to trap dust as it's coming in at the fans. With negative pressure you've got a lot of little places around your case and components where air (and dust) is getting sucked into the case. I'd rather clean 2-3 specific places (well, 6 for your set-up ) than have to go all over the case with a cloth or hand-vac cleaning every little crack. Been there, done that, don't wanna' go back.

But that's just me. Some people prefer negative pressure (and I still don't understand why) and either way you go it's still better to keep it well balanced. Every fan is negatively effected by pressure whether it's outgoing fans straining for lack of air or incoming fans trying to push against the pressure. To keep a good flow of air you need a good balance of CFM IN and OUT because that maximizes your fan's performance, which in turn maximizes the airflow in the case ...

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a good way is to use smaller push fans and larger pull fans.

I think you all are over complicating things. Just run the same fans on both sides of the rad and it will work well if you want to push-pull the rad. As for dust buildup in the rad, well it's going to happen no matter what you do. I just took my main system out yesterday and did a quick service on it and blew out the rads and man, the dust that came out of both rads was something. I'm glad a got an air compressor and that I had brought it outside. And believe it or not, I run filter grills on all the intake fans on my U2-UFO case, including the PA120.3 which is fed outside air from the front. I also changed out the waterblock from a Fuzion V. 1 to an Apogee XT and with the block changing and rad cleaning my average temps dropped from the high 40's to the low 40's while crunching Rosetta.

720x770 said:

a good way is to use smaller push fans and larger pull fans.

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Are you talking about push/pull on a rad or case airflow?

muddocktor said:

I think you all are over complicating things. Just run the same fans on both sides of the rad and it will work well if you want to push-pull the rad. As for dust buildup in the rad, well it's going to happen no matter what you do. I just took my main system out yesterday and did a quick service on it and blew out the rads and man, the dust that came out of both rads was something. I'm glad a got an air compressor and that I had brought it outside. And believe it or not, I run filter grills on all the intake fans on my U2-UFO case, including the PA120.3 which is fed outside air from the front. I also changed out the waterblock from a Fuzion V. 1 to an Apogee XT and with the block changing and rad cleaning my average temps dropped from the high 40's to the low 40's while crunching Rosetta.

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He's asking about case airflow (at least, that's what I was answering).
I would hope everybody uses identical fans in a push/pull for one rad!


Nice decrease in temps! Wonder how much of that is from the block change ...?

I'm not positive, but I think a good part is the block change. Not that the block is that much better, but rather the Fuzion was a used block and I never cleaned it out before using it. There was a little bit of junk caught in the pin array under the inlet area that I cleared out after the swap. The rest of the loop looks good and the water came out clear, so the junk might have been in there since I got the waterblock. It was time to do a spring cleaning on that system anyways. And I have an HK 3.0 to test against this XT too, so the system will be coming back apart in a few days for the HK tests.

have a 220 rad was 2 fans pushing fans at 75%duty cpu temps nice,,,,
same 220 rad with 2 more fans so in push pull , same exact fans, now fans are running at 40% and are virtually silent (hdd louder) little lower load temps and about the same idle temps....
my 2 pennies worth