regardless of noise, is higher CFM for a single exhaust fan ALWAYS better?

Turbonium

Platinum Member
Mar 15, 2003
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I know what CFM is. What I'm asking is if it's always the best choice to max out your CFM if noise isn't a concern.

I would assume yes. Convection, etc.

Case will have just the one exhaust fan.
 

996GT2

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Jun 23, 2005
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I know what CFM is. What I'm asking is if it's always the best choice to max out your CFM if noise isn't a concern.

I would assume yes. Convection, etc.

Case will have just the one exhaust fan.

Assuming you have decent intake airflow...yes.
 

richaron

Golden Member
Mar 27, 2012
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Assuming you have decent intake airflow...yes.
This. Not always better, usually tho. Depends on airflow coming in, some cases need higher pressure fans.

Most of the time my rig runs a single intake + filter. Case & performance needs specific; but I prefer positive pressure.
 

Turbonium

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Mar 15, 2003
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I literally have no intake fan. It just has a vent (situated "on top" of the CPU's HSF). I figure with an exhaust fan, it will help draw air in through the vent, due to negative pressure, and result in cooler internals.

Although I suppose this isn't technically negative pressure, is it? Since in always = out. I just want to get more air moving through the case (I assume that at present, warm air that escapes through the top exhaust vent is replaced by cool air... I just want to speed this process up).
 

richaron

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Mar 27, 2012
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I'm sure somewhere there is a pressure gradient :sneaky:

Yes above cpu is probably the best place for a fan to help convection. The question of higher cfm vs pressure ratings depends on how much area you have for air to flow in? empty fan slots? mesh etc
 

Turbonium

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Mar 15, 2003
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This is the case:

11-108-178-05.jpg


The case will be placed vertically, so that the left side in the pic is pointing up. That is where I will place the 80mm exhaust fan. The CPU HSF is directly underneath the other vent (the top of the case in the pic above). Just to clarify.

Again, there is technically no intake fan, but just that vent above the HSF with some relatively "wide" mesh as a filter - most of the air enters through here, given it's the easiest point of entry with the least resistance. The 80mm exhaust fan (which will go on the vent at the left side of the pic) I'm thinking of getting is rated at 27CFM.
 
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richaron

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Mar 27, 2012
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OIC. Sure, the higher the flow in that 80mm slot the better.

If want to visit crazyville, I think you should just remove the fan from cpu hsf & shove a single masive intake right above it :cool:
 

Meghan54

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Oct 18, 2009
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I'm sure somewhere there is a pressure gradient :sneaky:


Not much of one unless you measure directly in the flow of the fan. Since cases are pretty much a sieve---side panels aren't sealed, most cases have slot covers that have openings in them, etc., etc., it's pretty much as was stated above, in = out.
 

richaron

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Mar 27, 2012
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Not much of one unless you measure directly in the flow of the fan. Since cases are pretty much a sieve---side panels aren't sealed, most cases have slot covers that have openings in them, etc., etc., it's pretty much as was stated above, in = out.

Yes... Not much of one, hence sneaky eyes. Although it is all part of a continuum.

I think this in = out idea is confusing people, of course after equilibrium in = out. A positive pressure case isn't always increasing in pressure. Imagine it as latency, the in might have started first, then the out matches it's "speed". Having the same bandwidth =/ instantaneous.

I actually have 4 inlet fans in my case (no they are not running at the same time), if I turn them all on full speed it will still be in = out. But if someone tells me it's not positive pressure I'll think there's something wrong with them.

Edit: I think this was supposed to be more about the contiuum idea & less about bashing the in = out thing.
 
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aigomorla

CPU, Cases&Cooling Mod PC Gaming Mod Elite Member
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Sep 28, 2005
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CFM IS NOT STATIC.

STATIC is important when u need to push air.

CFM is important when you need to move the air inside something with no obstruction.

A Grill / Wall on the exhaust end / anything which can block the fan is an obstruction, so you want static more so then CFM.

And no... its not always the best thing..

If u have a fan in front of a radiator... u want static.
If you have a fan in front of a CPU u want static.
If you have a fan in front of hard drives.. again u want static..

If u have a fan in your front drive bay just bringing in air to your PC, you want CFM.
 
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