Intake fan to outake fan ratio

Xander2061 · 18 Feb 2007 at 00:41

My case has three fans attatched to it. Theres an 80mm intake fan on the front to draw air in over the HD. Then there's another 80mm on the side panel blowing air out of the case, and finally a 120mm fan on the air also blowing air out.

I want to turn the 80mm on the side panel around so that it looks better and doesn't shine so much light into my case (it has blue LED's on it and its detracting from my UV look inside the case).

I hear somewhere that you should either have greater intake or greater outake but I cant remember which. Is it going to be less effective to have the fan drawing air in?

stinka · 18 Feb 2007 at 10:13

you should have a better out take on the back of your case, sucking slightly more out than is being pushed in

ive got a Coolink SWiF-801 80mm i cut into my window blowing at my gpu its only like 20 cfm

ive got a 105 cfm YS-TECH FD1225 on back and a 64 cfm Scythe S-FLEX 1600RPM on front sucking in

ive also got a Akasa System Exhaust Blower sucking out a couple of slots below my gpu

this is ample in my modded antec p160 its like a wind tunnel
stinka

Xander2061 · 18 Feb 2007 at 12:18

Is it noisy? My PC right now is very quiet. Also my case isnt suited to having a larger fan on the side.

pieman109 · 18 Feb 2007 at 12:21

/\/\/\/\/\/\/\ what he said. Its better to create lower pressure in the case than there is outside and as high pressure generally moves towards low pressure, air will always be drawn into the case which should be cooler than what is being exhausted at the rear. Ideally, a smaller fan drawing in, larger fan exhausting out.

stinka · 18 Feb 2007 at 12:58

Xander2061 said:
Is it noisy? My PC right now is very quiet. Also my case isnt suited to having a larger fan on the side.

yeh, it aint quiet but im always gaming so headphones/loud speakers can hear it but its not that unbearable

Xander2061 · 18 Feb 2007 at 15:18

Great explanations, thanks for the help guys.

Captain Fizz · 19 Feb 2007 at 10:44

I would say the opposite.

Compared to the amount of air fans push, a little higher or lower pressure would make next to no difference.

Equal to slightly more intake than exhaust.
This means that dust only enters the case via the intake fans.

If you have low pressure inside the case, dust comes in at every available opening.
Over PCI cards, behind mobo, inbetween CD drives etc.

If you have more intake than exhaust - The only dust that collects is from and on the intake fans.
(If you use filters on the intakes, remember to increase the number of intakes by quite a bit)

pieman109 · 19 Feb 2007 at 12:58

Captain Fizz said:
I would say the opposite.

Compared to the amount of air fans push, a little higher or lower pressure would make next to no difference.

Equal to slightly more intake than exhaust.
This means that dust only enters the case via the intake fans.

If you have low pressure inside the case, dust comes in at every available opening.
Over PCI cards, behind mobo, inbetween CD drives etc.

If you have more intake than exhaust - The only dust that collects is from and on the intake fans.
(If you use filters on the intakes, remember to increase the number of intakes by quite a bit)

But therefore the air temp is gonna higher because the air inside the case is not being replenished enough with external cooler air which kinda negates the whole purpose of trying to lower temps as it were. The dust prob just means you've gotta clean it out a bit more regularly

Captain Fizz · 19 Feb 2007 at 13:25

pieman109 said:
But therefore the air temp is gonna higher because the air inside the case is not being replenished enough with external cooler air which kinda negates the whole purpose of trying to lower temps as it were.

IMHO - The difference is tiny.

I have tried various setups using one of my previous cases - Ran them with one fan turned round etc for some time - The difference in temp/airflow from having 'lower' pressure insude the case is not noticable - IMHO of course.

Air is still coming in, and still going out - As long as there is air flow going accross components, and cool air reaching heatsinks etc - Then there will be hardly any difference.

Most peeps forget their PSU acts as an exhaust anyway so usually have one more exhaust than they realise.

The difference between all fans at 12V and all fans at 7V is only 1 or 2 degrees IF the case is well designed / has had holes cut in it to make it cool better.
So the difference between having low or high pressure inside the case is minimal. (The difference in pressures is also miniscule when you compare it to any sealed system)

stinka · 19 Feb 2007 at 19:30

pieman109 said:
But therefore the air temp is gonna higher because the air inside the case is not being replenished enough with external cooler air which kinda negates the whole purpose of trying to lower temps as it were. The dust prob just means you've gotta clean it out a bit more regularly

in my experiance this is the case, and if you do a google search on fan placement this is the general opinion

gt_junkie · 19 Feb 2007 at 21:11

Captain Fizz said:
I would say the opposite.

Compared to the amount of air fans push, a little higher or lower pressure would make next to no difference.

Equal to slightly more intake than exhaust.
This means that dust only enters the case via the intake fans.

I agree with Captain Fizz -

I had a P180 and found it real annoying cleaning it every other month as it filled with dust! It had 1x120mm intake and 2x120mm exhausts (all running at the same low setting) in the main compartment. When i decided to remove one of the exhausts and up the intake fan to medium i quickly discovered no intruding dust and identical temps!

Due to that success i kitted out my server case in a similar fasion - although on a bigger scale!!! It presently has 3x120mm intakes (2x 5v and 1x 12v) and for exhaust an 80mm @7v and my tagan 580.

gt

Xander2061 · 20 Feb 2007 at 01:20

Aren't you both basically saying the same thing, more exhaust than intake?

gt_junkie · 20 Feb 2007 at 10:07

Xander2061 said:
Aren't you both basically saying the same thing, more exhaust than intake?

No, more intake than exhaust.

That will create positive pressure in the case and force air out of every available gap meaning dust will only try to enter the case at the intake fans.

Makes for a much cleaner pc if you have decent filters on those intake fans.

Look at it this way - Any temp gains from a negative pressure layout would quickly be lost due to dust build up on heatsinks which would lead to overheating components!

gt

pieman109 · 20 Feb 2007 at 10:52

"Look at it this way - Any temp gains from a negative pressure layout would quickly be lost due to dust build up on heatsinks which would lead to overheating components!"

Not if you cleaned it more regularly

Any ways, I've always worked on the principal that you need to get the warm out first (big 120mm fan exhausting) and pull cooler air in using a 120mm funning slower than the exhaust. Its all down to airflow really I reckon, you don't want a build up of warm air in the case which is where allowing components to get warmer.
In practice though, temps usually remain at or near a set point unless you've got summat mounted incorrectly like a cpu heatsink.

gt_junkie · 20 Feb 2007 at 11:04

pieman109 said:
Not if you cleaned it more regularly

I know. But it gets annoying!

I figure that if you don't want to then you don't have to! My temps didn't change so it was doing a similar job whilst not introducing biblical levels of dust!

Best thing for the OP to do is try both solutions and see which suits.

gt

stinka · 20 Feb 2007 at 18:01

my rig is in my lounge so i hoover it once a week when i do the house hold hoovering

its like a dust magnet inside

stinka

CaDLoN · 21 Feb 2007 at 16:04

I always had a preference for Positive case pressure i.e. more forced in than bening sucked out.

But all depends on youre preference & whats achiveable with youre particular rig & components

Snapshot · 22 Feb 2007 at 07:31

CaDLoN said:
I always had a preference for Positive case pressure i.e. more forced in than bening sucked out.

Same here. There's no point to the filter over the intake fans if the air is being sucked in round the optical drives, etc.

shadowscotland · 22 Feb 2007 at 17:28

My 2p worth

after 20sec the case reaches equalibrium: (numbers are unitless)
10 in + 8 out + 2 losses (via holes) = 10 'flow' (high pressure case)
10 out + 8 in + 2 gains (via Holes) = 10 'flow' + dust (low pressure case)
The 'flow' is the same, negative pressure has more dust

.

[slightly OT]
Air flow routes are more critical:
A direct 'flow' of 8 will have same cooling potential that a turbulent 'flow'' of 12.

.5 (distance) x 100 (temp gained) / 10 (flow) = +5 Case temp (baseline)
To reduce temps, reduce one or more of the three factors.

Less distance for air to travel (more planning/better case)
.4 x 100 / 10 = 4
Use a cooler chip (AMD / C2D)
.5 x 80 / 10 = 4
More air flow (Bigger/faster fan)
.5 x 10 / 12.5 = 4

Back to my example above to acheive base line temp.
.4 x 100 / 8 = 5 (A direct flow of 8)
.6 x 100 / 12 = 5 (turbulent flow of 12)

Practical usage:
So you've oc'ed your chip, 50% more heat .5 x 150 / 10 = 7.5 (to hot)
You have various options.
.5 x 150 / 15 = 5 (an extra 50% more air flow)
.4 x 150 / 12 = 5 (an extra 20% more air flow well routed)
.4 x 125 / 10 = 5 (Improved cooler plus well routed flow)
.01 x 150 / .5 = 3 (liquid cooling direct on heat source, water flow 1/20 of air)

[/slightly OT]

CaDLoN · 22 Feb 2007 at 23:59

Holy Flaps Batman!!! i've only had 8 beers & am completly flaberghasted!!!

Simple version, blast more air in wher ya want it = good stuff, it'll find its own way out so dont worry too much about extraction!!!

4 x 8 8.246 / pie * 33 + 9 = a load of b0ll0x :confused:

Trial & error is the bst way for your box & equipment, plus its more fun that way
Go have fun tinkering with a load of fans