Duct Question for the Experts

[goobee]

I want to run a duct from a 92mm fan on the bottom of my case to a 92mm fan on a SK6 heatsink. Should the fans be:

A.) Both with the same cfm?
B.) Intake higher cfm than the one on the hs?
C.) Intake lower cfm than the one on the hs?

I actually have 2 fans on the bottom of my case. Would it be more effective if I did like a "Y" and used both to force air on to the hs?

 

[Nessism]

Well first off I have to fess up and admit that I've never messed around all that much with stuff like ducting. Have had a few thermo classes in school however.

My guess is that it won't matter much which way you go fan wise. The intake fan will provide positive pressure in the duct feeding air into the CPU fan. This pressure may help feed a little extra air onto the heatsink but not all that much. I think the main benifit of a duct is to provide cool outside air to the cpu.

I'm thinking of building an exhaust duct similar to that used by Fong Kai. This way I will be pulling hot air out of the case. I think this is more important. Standard rule of thumb, the exhaust must be larger than the intake. This is the reason it is better to put the case fans on the back first - exhaust, and on the front second - intake.

Ed

 

[Woodie]

I have to jump in here...for normal ventilation purposes, like maxing CFM, Nessism is right, you deal with the exhaust side first. But, in the case of a PC case, the issues associated w/ having a negative pressure in the case means that air is sucked in from all areas on the case, allowing dust to enter w/ the air.

It's usually considered better practise to have a slightly positive pressure in the case, so all air intake is throught the intake fan and filter, allowing the filter to do its job of preventing (reducing) dust inside the case. Ducting the intake to the CPU is considered more effective, because it brings the coolest air (ambient) to the hottest point (the CPU). I'm don't know how much benefit there would be to putting an intake fan on the duct, but I suspect it would add significantly to the volume of air. That's because "pushing" air is easier than "pulling" air.

As usual, my advice is worth exactly what you paid for it, unless you're a subscriber, in which case you got ripped off!

 

[Nessism]

Woodie wrote:


<< It's usually considered better practise to have a slightly positive pressure in the case, so all air intake is throught the intake fan and filter, allowing the filter to do its job of preventing (reducing) dust inside the case. >>



FILTER?

I like your suggestion to have filtered incomming air. Many people, such as myself, often neglect this.


And suggestions on the best way to add a filter to an Antec 800 series case?

Ed

 

[Woodie]

<< And suggestions on the best way to add a filter to an Antec 800 series case? >>


Who are you kidding?? I'm still running my workstation w/ the cover off!

Seriously though, I'm hoping to build a small (half-height) rack mount cabinet to house them in, so I can filter the cabinet, rather than each individual device.

 

[goobee]

Rather than doing a complete duct, (doing an intake that feeds to the hsf then back out of the case) so that the air is completely isolated from the air inside of the case, my plan is to draw outside air directly to the hsf from an intake duct to the hsf's fan. Is that a feasible plan or should it be a complete ducting?