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FEATURED Positive case pressure vs Negative case pressure

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Positive Pressure VS Negative Pressure

  • Positive Pressure

    Votes: 238 53.0%

  • Negative Pressure

    Votes: 92 20.5%

  • Peer Pressure

    Votes: 52 11.6%

  • Who cares?

    Votes: 67 14.9%
  • Total voters
    449
Status
Not open for further replies.
I voted positive but i currently run my mainrig open air on my testbed.

The HTPC is positive with filters at intake. 2x140mm intake and a single 140mm exhaust.
 
briansun1 said:
what I am more suprised about is that there are not more drawings of the case with fans. any resons?
Click to expand...
Why would there be more of that? Its pretty easy to conceptualize with words, to me, what the airflow is doing... its a lot quicker to type than to make a terrible MSPaint (well, IM terrible at Paint, LOL!)
 
EarthDog said:
Why would there be more of that? Its pretty easy to conceptualize with words, to me, what the airflow is doing... its a lot quicker to type than to make a terrible MSPaint (well, IM terrible at Paint, LOL!)
Click to expand...

touche

I guess it is just me then because I suck at writing and can draw better then I can write.
I would think it is easyer to just draw it. but then everyone is diffrent
 
I currently run my main computer with positive pressure (230 CFM in/180 CFM out), I've had it as high as 300 CFM in/180 CFM out. I've got it on a fan controller, so I can balance the airflow however I like by shutting off fans or choosing between high/low speed.

I've tried both positive and negative setups, and I see no difference in temps between the two (provided there are both intake an exhaust fans spinning).

I did notice though that having only intake fans or only exhaust fans was worse than slightly positive, slightly negative, or a balanced airflow setup, by a good 5°C+.

I also found that an open case or test bench typically had lower temperatures than both positive and negative airflow setups.

My results involve a case who's design and internal airflow patterns are good enough that there is no discernible difference between positive and negative.

In past testing with an old less-efficient case though I did notice better temperatures with a positive setup than negative, I believe that result dealt more with my case not having enough airflow than to negative pressure being outright worse than positive.
 
There's a lot of variables involved. More than I want to go into for sure. I've managed to get my case quiet with 2-5c increase in case temp dependent on GPU mostly. I have 6 HDDs and a passive HD5770 GPU so of course there will be some heat in case. My case fan speed is based on CPU heat; 660rpm idle and 950rpm @ 48c on 980 on extended 100% load but no GPU as obviously even surfing jitters at 100% load.
 
Tech Tweaker said:
I currently run my main computer with positive pressure (230 CFM in/180 CFM out), I've had it as high as 300 CFM in/180 CFM out. I've got it on a fan controller, so I can balance the airflow however I like by shutting off fans or choosing between high/low speed.
Click to expand...


you don't have either! you have a damn hurricane in that thing!:rofl:
 
I would love to try a positive pressure setup, but I am seriously lost how that could be effectively done with a layout like mine (which seems to be quite popular). I have one rear 120mm plus two top 120mm fan spaces on both of my full-size towers. It would seem that all three of those locations are poor choices for intake fans.

Unless I were to intentionally pick slower fans for these locations, which would seem like a poor idea, wouldn't I need to find a minimum of four 120mm mounts elsewhere for intake? One of the two cases has room for dual 120mm fans up front and a single 140mm side. The other has a single 120mm front and single 120mm side. Are people with positive pressure simply not installing fans in the top spaces on their case, or are you all running multiple side/bottom intakes?

*edit*

I also just noticed lots of people seem to take their PSU into account when figuring their air pressure. Since 95% of performance cases are bottom-mounted, shouldn't this be a moot point? The air is coming from outside (under) the case and being pushed out the back- it never actually figures into the internal airflow of the system at all....
 
Last edited:
cfm specs are very very deceptive compared to reality.

216cfm is moving a 6x6x6' box of air every 60 seconds. Average case is approx. 2 cubic feet. That would be changing all of the air in the case 108 times a minute. Once every .55 seconds.

Lets say a case has 3 intake fans rated 73.6cfm @ 1300rpm with no restriction. Drop that to 700rpm with grill, filter, HDD cage, GPU cabling, and back grill and
I'm maybe moving 20-60cfm through the case..
which is changing the case air 10-20 times a minute..
that's new air in case once every 3-6 seconds.

So how much air is that 200-300cfm fan setup really moving? :D
 
Last edited:
doyll said:
Lets say a case has 3 intake fans rated 73.6cfm @ 1300rpm with no restriction. Drop that to 700rpm with grill, filter, HDD cage, GPU cabling, and back grill and
I'm maybe moving 20-60cfm through the case..

So how much air is that 200-300cfm fan setup really moving? :D
Click to expand...

Well, if we're talking about benchmark rigs, who said anything about needing filters, an HDD cage, or even a 3.5" drive to much things up? All I have is another pair of 80+ cfm rated fans in the middle helping ram the air through the heatsink and out the back ;)
 
Indeed.

So how much air is a 200-300cfm fan setup really moving with no filters? Is it enough to completely change the air in a 10' x10' room every 3-4 minutes.? :D

Edit: It's fun to talk about it. Main thing is that it does what you want it to do. ;)
 
I got positive pressure with a box fan blowing on my dog who just got out of the pond.

This thread has hashed it all and no one reads it all anymore.

It's a 'on the street' comment type of thread now. A lot like a short segment on the funny late night talk shows.

Still, it might have value if someone could extract the early 150 good comments and let the rest go to..............

We haven't reached Jerry Springer rehash release 17.5 yet at least. That video is gonna be really lame, but we are close here.
 
doyll said:
Indeed.

So how much air is a 200-300cfm fan setup really moving with no filters? Is it enough to completely change the air in a 10' x10' room every 3-4 minutes.? :D

Edit: It's fun to talk about it. Main thing is that it does what you want it to do. ;)
Click to expand...

That really depends on the fan. If it's a benching setup, yes. I used three taped together and stuck in a window to ventilate my whole house a couple summers ago. They'd pull the door open if it wasn't latched. Pulled the catdoor open too.
 
Bobnova said:
That really depends on the fan. If it's a benching setup, yes. I used three taped together and stuck in a window to ventilate my whole house a couple summers ago. They'd pull the door open if it wasn't latched. Pulled the catdoor open too.
Click to expand...

Did you have to wear googles when you entered the room? LOL

What fans were they?
 
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