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front intake pointless?

A

albumleaf

Senior member
I have two 120mm fans in my case along with my psu fans.. the front 120mm fan can't pull in any more air than the back one can push out, so why not just let the rear 120mm fan and the psu run and let air passively enter the case through the front opening reducing noise?
 
If the front fan isn't taking in much air, taking the front fan out isn't a bad idea.
It is not necessary I believe.

-Frank
 
The front fan is good to keep more airflow in your case. I can't really explain it, but someone else should be able to.
Also, it will keep your front components cooler by forcing air in.
 
You could theoretically get away with this however you will most definitely see a reduction in total airflow throuh your case and a subsequent rise in case temp. 2 fans pulling air simply can not pull the same airflow as 2 fans with an assist fan pushing air into them. Also it will completely change the airflow dynamic within your case and possibly create hot spots where none existed before. i'm not saying that the difference would be drastic, just that there is no way it would be equivalent.

If you don't believe this, take two room fans and place them so one blows into the other.....then turn the one off. You'll see what I mean.

Add to this the fact that your hard drives may run hotter and you are probably ahead to keep the front fan running. If noise is your main consideration, why not buy a fan controller and you can back the fans off a bit when you desire a more quiet enviornment and then crank them back up to speed when you are gaming etc and really need the cooling?
 
Yeah you defintitely need some air coming into the case. I use a side and front intake and then exhaust fan below the PSU.
 
I go with the more air out version simply because heat from the sinks expands the air allowing the sinks to work more efficiently. The exhaust fans should be closest to the heat source to get it out. The front fan I aggree helps keep the botton HD cool and the southern district of your mobo. The idea is that you want plenty of exhaust and a breeze on the non-actively cooled parts (Southbridge, ram, mosfet regulators.

With just 1 or 2 120 exhaust fans, you might consider ducting incomming air to the following regions.
1 HD: array put a grill and filter in a 3.5 or 5.25 slot right in front of the drives.
2 South bridge. consider a small 40 mil fan blowing up accross the SB to the Ram (on most boards this works).
3 Ram(s) See#2
4 Video, if it is a ATI9800, Nvidia6800 or greater and does not have it's own exhaust fan not counting the little muffin fans that blow air accross a headsink. Put a slotted PCI slot below the card so that incoming air hits the face of the card.
5 Northbridge and CPU consider a duct that drops outside air right into the HSF of the CPU, on most systems this covers the NB also.

I'm considering a PVC pipe mod where I pipe in air from the from grill through a filter with a series of holes a reducer and 45 elbow directing airflow right to the hot spots listed above. My intention is to use the rear exhaust, psu, NB and Video fans only letting the ducting do the rest. Note my rear exhaust fan is my CPU fan(tt103 Heatpipe).

 
It's better if you have a negative pressure system - if you have more CFM flowing out than being taken in by forced air (fans), it'll create a negative air pressure and draw air in, causing more efficient ventilation.
 
Because then you'll have dust clogging up any cracks in the front of the case (including CD drive bezels) and your HDs won't get any cooling.
 
if you file holes to make them larger so the front 120m can get airflow it would help because 1) it brings air from outside your case into it and its usually colder, and it redirects to colder air to the back half were the mobo and everything is
 
I actually noticed a 5 degree temp drop when I have a front intake installed in the case. I dind't think it would make any difference at all, but it did.
 
Originally posted by: ariafrost
It's better if you have a negative pressure system - if you have more CFM flowing out than being taken in by forced air (fans), it'll create a negative air pressure and draw air in, causing more efficient ventilation.
Click to expand...
While it is true that having an exhaust fan will create suction, it will not create more efficient "ventilation." The key parameter that you want to look at is what actually achieves 'ventilation' - it is the velocity of air moving in the case. The higher the velocity, the more the air will be able to dissipate heat.

Now, the question arises: how do you know what the velocity in the case is? Simply put, you don't. It will vary from point to point within the case. So, you can only get a qualitative idea. Fluid dynamics tells us that the larger the pressure gradient, the higher the velocity of the fluid and, therefore, the more cooling will occur. By having an intake fan, you are maximizing the pressure for the exhaust fan so that it may create higher velocities in the case. If you remove the intake fan, then the velocities will be much lower.
 
Originally posted by: AlabamaCajun
I go with the more air out version simply because heat from the sinks expands the air allowing the sinks to work more efficiently. The exhaust fans should be closest to the heat source to get it out. The front fan I aggree helps keep the botton HD cool and the southern district of your mobo. The idea is that you want plenty of exhaust and a breeze on the non-actively cooled parts (Southbridge, ram, mosfet regulators.
Click to expand...
What you say would be true if the airflow in the case was poor to begin with. However, if you have any reasonable level of airflow around your sinks, then the 'expansion' of air due to heat conduction should play a negligible role in the overall heat transfer. The expansion of air due to heating would cause natural convection - the flow of air due to density differences. This only becomes a real factor when the air around the sink is stagnant.
 
Front intake also helps stir up the air inside the case to prevent hot spots. It's an unusual case that won't do better with a nice 120 up front.

.bh.
 
Originally posted by: albumleaf
I have two 120mm fans in my case along with my psu fans.. the front 120mm fan can't pull in any more air than the back one can push out, so why not just let the rear 120mm fan and the psu run and let air passively enter the case through the front opening reducing noise?
Click to expand...

That is not entirely true. The air inside your case is not only the one your front fan intakes; besides, I am certain your front fan is somehow obstructed by your case.

I agree that the front fan is a great way to keep the airflow constant in your computer, still, there would be no need for it if:
a.- the rear exhaust fan air is not hot or warm at all
b.- your hard disks are under 38°C
c.- you do not have a high end videocard.
 
two fans in series only increase the likelyhood of reaching the max airflow of the single fan. only necessary if the case is restrictive.. else it might not help much at all.
 
Originally posted by: 0roo0roo
two fans in series only increase the likelyhood of reaching the max airflow of the single fan. only necessary if the case is restrictive.. else it might not help much at all.
Click to expand...
Not really... If you only have one fan, you will have stagnant regions in your case. Air will choose the path of least resistance, which would not include your PCI/AGP slots, and just bypass the heat-generating portions of your case. This is exactly why intake fans on the front of the case are typically at the bottom and exhaust fans on the back are at the top.
 
well, given that i have more air outflow than inflow, i think i'm just going to yank the fan out and see how my temps do.
 
Originally posted by: albumleaf
well, given that i have more air outflow than inflow, i think i'm just going to yank the fan out and see how my temps do.
Click to expand...
How did you quantify that you have more outflow than inflow? Just curious.
 
running without front fan is perfectly fine as long as your harddrive doesnt overheat. if you seal all other openings in the case - forcing the rear fan to take in air only from the front 120mm fan hole, the hdd may still get enough air.

I run a 120mm fan at 6V for the front. Inaudible, and it blows just enough of a wisp of airflow over the harddrive to keep it happy.
 
Originally posted by: CycloWizard
Originally posted by: albumleaf
well, given that i have more air outflow than inflow, i think i'm just going to yank the fan out and see how my temps do.
Click to expand...
How did you quantify that you have more outflow than inflow? Just curious.
Click to expand...


i have two 120mm fans (1 front, 1 back) and two 80mm fans in my ps that exhaust into one. Thus, i have more airflow out the back than i do coming in the front.
 
Originally posted by: Tiamat
running without front fan is perfectly fine as long as your harddrive doesnt overheat. if you seal all other openings in the case - forcing the rear fan to take in air only from the front 120mm fan hole, the hdd may still get enough air.

I run a 120mm fan at 6V for the front. Inaudible, and it blows just enough of a wisp of airflow over the harddrive to keep it happy.
Click to expand...


the fan in the front of my case is practically inaudible.. but it's in one of those goddamn thermaltake fan brackets and because of the way my case is made, i can't screw the fan directly onto the case chassis.
 
I've got several cases running on slight negative pressure and dust is not a big problem though once a year I have to blow out the inside of the case, i Have cats too.

Creating a faster moving draft will not necc. cool more efficiently due to the amount of bypass you end up with. Yes the expansion is minimal but in all case just as others have stated it is still more effiecient to draw air out, the inflow is best for turbulance and in most cases the intake is mounted away from the from panel an is not really sucking in from outside but happens to be where most of the intake air comes in. What I've seen is the intake fan blasts air out in a cone thus hitting the walls and bottom of case and upper HD(yes cools lowest drive) and then proceeds to bounce around the case and moves a lot of air at the PCI slots and Video. Ive also observed with streamers that the air hitting the bottom HD accually swings upward and creates an occilation around the dimms and northbridge area. Beyond that point I saw no further benefit as the exhaust draft is working on the area around the cpu and mosfetVRs. With all cases differing slightly, this scenary varies somewhat.
<strong>Flow chamber test!</strong>
If you don't have a window case, use a sheet of plexy to cover the side. Tape 1/8 inch by 4 inch long plastic streamers to the bottom of lowest drive, bottom edge of VGA, one near the top of your dims and one near your northbrige. Just be sure none of them get sucked into your fans. Power up the rig and place the plexy against toe opening. You sould see movement in all the streamers. If not, you may have to tidy ups some cables especially those flat ATA cables (fold them in half along the length to reduce size. make sure none are hanging below the HDs, zip tie them to the side if they do. Stuff extra cables on top of floppy or CDRom drive away from the warmer drives and away from the MOBO airspace.

Improve Airflow and Quieter Fans, cut out punched metal cheese grater slots and lovers, replace with the wire type grills.
 

the fan in the front of my case is practically inaudible.. but it's in one of those goddamn thermaltake fan brackets and because of the way my case is made, i can't screw the fan directly onto the case chassis.[/quote]

Double sided foam tape! Stops rattles and keeps stuff in place.

Would'nt that be a "Thermaldamn" fan bracket :G
 
Originally posted by: AlabamaCajun
Creating a faster moving draft will not necc. cool more efficiently due to the amount of bypass you end up with. Yes the expansion is minimal but in all case just as others have stated it is still more effiecient to draw air out, the inflow is best for turbulance and in most cases the intake is mounted away from the from panel an is not really sucking in from outside but happens to be where most of the intake air comes in. What I've seen is the intake fan blasts air out in a cone thus hitting the walls and bottom of case and upper HD(yes cools lowest drive) and then proceeds to bounce around the case and moves a lot of air at the PCI slots and Video. Ive also observed with streamers that the air hitting the bottom HD accually swings upward and creates an occilation around the dimms and northbridge area. Beyond that point I saw no further benefit as the exhaust draft is working on the area around the cpu and mosfetVRs. With all cases differing slightly, this scenary varies somewhat.
Click to expand...
You're going to have to define your terms a little better if you want to make such sweeping generalizations. A faster local velocity will always create more heat dissipation in that locality. Further, it will induce greater turbulence, meaning bypassing should decrease as mixing and fluctuations increases.
<strong>Flow chamber test!</strong>
If you don't have a window case, use a sheet of plexy to cover the side. Tape 1/8 inch by 4 inch long plastic streamers to the bottom of lowest drive, bottom edge of VGA, one near the top of your dims and one near your northbrige. Just be sure none of them get sucked into your fans. Power up the rig and place the plexy against toe opening. You sould see movement in all the streamers. If not, you may have to tidy ups some cables especially those flat ATA cables (fold them in half along the length to reduce size. make sure none are hanging below the HDs, zip tie them to the side if they do. Stuff extra cables on top of floppy or CDRom drive away from the warmer drives and away from the MOBO airspace.

Improve Airflow and Quieter Fans, cut out punched metal cheese grater slots and lovers, replace with the wire type grills.
Click to expand...
You could just get some dry ice and set it in front of the intake, then pour some water on it. 😛
 
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