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Quick Fan Question. HELP

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moosedick

Member
Joined
Apr 17, 2001
I have an enlight 7237 case with a pIII 700 mhz. I have an intake fan and an exhaust fan (one is more powerful than than the other by about 5 cfm). Here is my question: Should I have the more powerful fan taking air in or blowing it out the back?
 

e_storm

Member
Joined
Mar 16, 2001
Location
Chicago, IL
I'm certainly no expert, but from what some of the cooling gurus have said, sounds as if positive pressure in the case is better than negative.. meaning that you would want more cfm blowing into the case. I don't know if a difference of 5 cfm in either the negative or positive direction will make that much of a difference though... but again I'm no expert. Keep in mind that the psu is exhausting case air too.
 
W

William

Guest
you are actually going to have a slight negative pressure if you take into account your PSU fan. There is a debate on what is better, but what is more important is having good airflow and low case temps, how you get those varies. For instance, Hoot with cohesive air cooling only uses one BIG fan and gets great temperatures. How far are the case temps off of ambient? If you are within say 5C then you are doing great.
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
I modde the front and rear fan oipenings on my 7237 to accomodate 92mm fans, but if you want to use 80s, Go with something like the Sanyo Denki 44cfm blowing in and a Sunon 36cfm blowing out. Furthermore, I tried both ways and here's what worked best for me. If your HSF blows into the HS, bring air in the rear and out the front. If your HSF draws air out of the HS, bring air in the front and out the rear. Please don't parrot the "Oh but heat rises..." phenomenon. That only matters with no forced air circulation.
Lastly, again from my experience, For greater than, or equal to, 70W CPU overclock setups (1.33 @ 1.75V), in a mid-tower, I recommend a minimum of 55cfm thru-case circulation. That much flow overcomes eddy currents that tend to create dead-air spots. Run that amount of unidirectional, thru-case airflow and your box will run a few degrees above room, at the most. The Sanyo Denki 92x32mm fans deliver such performance and are quieter than many 80mm fans delivering less airflow.

For a Full tower, I would use two Panaflo 120x38mm 86cfm fans to achieve unidirectional thru-case airflow, or two pair of the Sanyo Denki 92x32mm 55cfm fans.

Defintiely shoot for "in one end, out the other" aka unidirectional thru-case flow, no matter what you wind up going with. Having a guzzillion fans blowing every which way can be detrimental to performance.

Hoot
 

SCOdoubleT

Registered
Joined
Apr 30, 2001
I've always heard that you want the fan nearest to the HSF to be blowing out. That way hot air would be removed from the CPU and the case, this will help keep both temps lower. I have 1 80mm fan blowing in, in the front and 1 80mm blowing out in the back, and another slot cooler blowing out in the back. I think it's more important to remove the hot air, then fill the case with air that can't be removed as quickly.
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
Think about this model a second. Air is drawn into the HSF, blows down through it, deflects off the baseplate and washes out on all sides of the bottom. Right up above the HSF is an exhaust fan. That washed out, warmer air gets coaxed up towards the exhause fan, where it goes past the HSF intake again. Some of it goes back down through the HSF and the cycle repeats. If the fan next to the HSF is blowing cooler air in from outside the case, a lot of it gets sucked back down into the HSF, exits like the above description and since the lower front fan is on exhaust, that warmer air moves away from the HSF towards the exhaust fan, while more cooler air continues to come in next to the HSF intake. Some people balk at the idea of drawing that warmer air across their motherboard as it heads towards the lower front exhaust fan. The air is not that much warmer if you have enough of it passing through the case. I've tried it both ways many times, with many different combinations of case fans and using the rear entry approach yields about 2-3C cooler CPU.
 

Phil

Senior Member
Joined
Jan 13, 2001
Location
Bolton, UK
Hoot (Jun 20, 2001 11:55 a.m.):
Think about this model a second. Air is drawn into the HSF, blows down through it, deflects off the baseplate and washes out on all sides of the bottom. Right up above the HSF is an exhaust fan. That washed out, warmer air gets coaxed up towards the exhause fan, where it goes past the HSF intake again. Some of it goes back down through the HSF and the cycle repeats. If the fan next to the HSF is blowing cooler air in from outside the case, a lot of it gets sucked back down into the HSF, exits like the above description and since the lower front fan is on exhaust, that warmer air moves away from the HSF towards the exhaust fan, while more cooler air continues to come in next to the HSF intake. Some people balk at the idea of drawing that warmer air across their motherboard as it heads towards the lower front exhaust fan. The air is not that much warmer if you have enough of it passing through the case. I've tried it both ways many times, with many different combinations of case fans and using the rear entry approach yields about 2-3C cooler CPU.

Did you see my diagram? :D
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
You're talking about Justins thread Phil? Yes, I did. The blowhole makes all the difference in the world.

Hoot
 

Hoot

Inactive Moderator
Joined
Feb 13, 2001
Location
Twin Cities
With a Radio Shack Nibbler for the sheet metal, a hand drill for the mounting holes and "A Cool Hand, a Keen Eye and Horse Sense". ;D

Hoot
 

Kingslayer

Senior Member
Joined
Jun 12, 2001
Location
Port Charlotte, Florida
The one thing that I have noticed is that if you put the more powerful fan blowing in, and the less powerful sucking out, you will shorten the life of the more powerful fan. You create a positive pressure, and the more powerful fan has to work harder.

Big whoop fans are cheap, but I found it interesting.

The big thing is that every case is different. Coming here and asking the question you did didn't really give you a direct answer. But, with the answers you got you recieved knowledge on what to watch out for and the basic concept of cooling. And that is much better than "put the big fan here". Because every case is different, and different hardware makes different impacts in the flow, you can now judge your answer on your own.

And yes, blowholes make a huge difference. I was skeptical at what the could really accomplish. Put one in the wifes machine and I was amazed.