Suck or blow?

[mh2360]

Now that i've got your attention...

I was fitting a new case fan when it occured to me, is it better to blow cool air into the case or suck the hot air out, in order to keep the system cool?

[greymalkin]

most every cooling system ever made works off the same principle....get the heat out...the cool air will come in as a result.

the vague topic descriptions are generally not helpful.

[gadgetguy]

In general you want to expel the heat so if you only use one case fan it should suck the heat out. If you use multiple fans and your case is designed for it, it's better to create a flow with one end pulling air in and the other pushing the hot air out.

[Bodyslide]

2 fans on the Front of the case pulling air in, then one or 2 fans pulling the hot air out.....

[lordsmurf]

2 fans on the Front of the case pulling air in, then one or 2 fans pulling the hot air out.....

This is the winner.

[redwudz]

I like 2 intake fans in front, blowing over the hard drives and two exhaust fans in back. Low RPM if you don't like noise, 120MM low RPM even better.

[ROF]

Now that i've got your attention...

I was fitting a new case fan when it occured to me, is it better to blow cool air into the case or suck the hot air out, in order to keep the system cool?

Both is considered optimal. Typically a tower case is fitted with fan ports in the back, front, and side. If you have a side port you should exhaust the air out since your processor fan is usually close by blowing air that way anyways. The front fans are typically located in the bottom of the case, which is a good place to intake fresh cool air. The fan is the back of the case located about midway up the back of the case should be the main exhaust since it will exhaust radiated heat from your power supply and processor out of the case. In order for any case cooling system to operate efficiently any case covers should be securely in place.

[CrayonEater]

2 fans on the Front of the case pulling air in, then one or 2 fans pulling the hot air out.....

That's how I do it.

[DarrellS]

That's how I have mine also (2 front intake, 2 back exhaust and a horn on the side for the processor fan) but I was reading somewhere that it is a good idea when you buy a case to to drill holes in the top of the case (or one big hole and a screen), in front of the power supply and above the processor and mount an exhaust fan there to get rid of the heat that rises to the top.

I've also thought of connecting something like dryer hose and running the hot exhaust air out of the house instead of into the room where it gets pretty warm if you're not running an efficient air conditioner.

[redwudz]

I've heard that before about having a top exhaust. Probably the best way as heat rises, but most people don't want the noise of a fan blowing out the top. You could check the temps near the top of the case. In all the computers I've assembled, the PS fan sucks out any warm air near the top, so that idea doesn't seem worth the effort.

I also have a problem with some cases blowing air into the CPU cooler from the side. If the fan doesn't have a filter on it, they tend to blow all the dust in the air directly into the CPU cooler, which may cause problems in the long run. The front intake fans don't seem to have that problem. Really, if you need that much cooling, you might try a different CPU or CPU cooler. JMO.

I have known a few people that exhaust the hot air from the case to the outside. It's also a way to cut down the noise from the exhaust fans. It's a nice luxury if you can do it.

[dvd3500]

Tests done back in the 90's showed that as far as CPUs were concerned blowing air onto the heatsink showed a marginal improvement over "sucking".
Case wise though everything here is what is always said. Get the air moving. Turbulent air always cools better.

[ROF]

I also have a problem with some cases blowing air into the CPU cooler from the side. If the fan doesn't have a filter on it, they tend to blow all the dust in the air directly into the CPU cooler, which may cause problems in the long run.

Actually I find this kind of setup in most cases(no pun) to be absurd. Most modern CPUs have a Fan/Heatsink combo. This fan typically blows the hot air upwards and away from the chip. Upwards being towards the side of the case. If you add a fan on the side blowing air back towards the CPU(this side fan is usually twice the size of the CPU fan) you are actually defeating the purpose of your CPU cooler.

[lenti_75]

suck AND blow....this is the way

[ROF]

I look around for TGPO when I need alot of hot air blown out of my case.

[ViRaL1]

So the consensus is blow the front, suck the back?

[SingSing]

My experience is blowing at the most likely to fail part, if you want to start at the minimum - one fan. Pc is an electronics system, and it will certain go down in single point failure. The most likely candidates are CPU, Harddisk, GPU, MOBO chip.

The enclousure engineers I have worked with, calculate heat disspation/flow based one fan-in, and create positive pressure that drive hot air out, because there is always one crucial candidate that is targeted for cooling.

This is like prefered give the handout to most needy vs donate to united way.

The ingress fan should be at the front, where cold air will be availabled. The back of the PC is warmer because the back of the PC are nomrally restriced by table, wall and clogged with cable, plus the existing heated power supply.

[ozymango]

Having had to come up with various creative ways of getting the heat out of water and air-cooled car engines over the years, I approach computer cooling from an aeronautical point of view.

Okay, don't mean to be too serious, but seriously, a lot does depend on case design, intake location, exhaust location, and component location. Got an old server case that has intake fans in the front bottom, exhaust top back, but if you stack two drives in the slots, the top drive gets very hot because whoever designed this case (and it's an old case) didn't understand the weird mechanics of air and fluid flow. Also the bottom drive blocks the top drive from getting air.

I'd say it's not so much a question of blowing or sucking, it's of air flow. Generally speaking, if you "blow" on some component, you sorta guarantee that the air flows over that component. That is, moving air from a non-ducted source (i.e. just air blowing from a fan, no tubes, no diverters, no barriers, no channels) can be "aimed" at a component. Therefore, the moving air moves across that item, removing heat, and thus the component is cooled.

If the air is "sucked" around a component, there's your need for channeling or ducting of some form because you want that air to move around that component. A "sucking" fan doesn't care where it gets the air from, and if it's easier to pull air from the wasted space between the fan and component versus the little heatsinks on the component itself, it's gonna pull the air from the wasted space. Which is why you see some kind of "ductwork" inside any decent computer case or mb fan nowadays, to force the air to flow in a specific path.

Whether it's blown or sucked is immaterial, it's where the flow is routed that makes the difference. Thermodynamics is what it's all about!

[ROF]

So basically it doesn't matter if you suck or blow as long as you are doing it correctly?

[ozymango]

So basically it doesn't matter if you suck or blow as long as you are doing it correctly?

Well, I can only speak from my own experience ...

EDIT: And when blowing or sucking, those computers can carry all sorts of viruses, make sure you use proper protection at all times!

[SingSing]

So basically it doesn't matter if you suck or blow as long as you are doing it correctly?

* Blowing at a component is directional. I expect my CPU fan is blowing at the CPU. Non-ducted sucking from the volume is non-directional.
* Cooling a PC is related to cooling Electronics. The verification is to tape thermo-couples on those most likely to fail components and find out the decreament of their temperatures.

[vhelp]

Recently, I had to clean my CPU fan (one on the chip) and to my surprise,
it had (how shall I say) caked on dust in all the heat-zink's fins.

I don't know about you or other's here, but my instints tell me that this
is equivalent to putting on a blanket over the heat-zink's fins, which
adds *more* heat -- blocks the heat from escaping efficiently (faster) and
can only do more harm.. probably like causing the zink glue to detach.

..

Now, I'm still using my ECS brand mobo, K7S5A w/ an AMD 1800+ cpu in it.
This mobo was thought to be dead, until a previous blow-out of another
mobo caused me to run around crazy for any spare mobo's. And it was only
out of pure random "what-if", that my ECS K7S5A mobo was near by for me
to test. Long story short.. I don't recall what lead/made me believe that
the mobo was dead in the first place, but which lead me to the other mobo
(which died recently) and bringing me back to the ECS K7S5A mobo -- pretty
if you ask me.

But, the reason why I bring this up, is because I recall in a previous fan
insident (which I posted here a couple of years ago, I think) where my fan
was not on, and my cpu was baking -- hence, blew out. And, as I was trying
to say, in this latest and recent CPU/MOBO event of mine, I was cleaning my
cpu fan, and to my surprise, all of the fins were stuffed with this very
thick blanket of dust, and all caked in between each fin. So what caused
all this dust in the first place ?? Well, long story short.. I had screwed
the fan on the wrong side -- Top was screwed in, Bottom'wise
And all the air (and dust) was being pulled into the fins.

So, now try to imagine this happining on a larger scale.. say, your cpu case,
where all this air (and dust) are being focused into your case, with little
room to escape. Over time, what do you think will happen ??

I'm sure some of you know the answer

-vhelp 4082

[beric3236]

If you are concerned about noise I found a new fan, and no this is not a hijack just information, that is whisper quiet. It is produced by a company call enermax and has a db rating of 14, which I believe as I had it up to my ear and hardly heard the fan. My only regret on this fan is that they don't make one for the cpu size. Oh BTW - Don't forget to put something in front of the fan in the front of the case to help keep the dust out. If not you will have to blow the machine out on a regular basis.

[dvdguy4]

2 fans on the Front of the case pulling air in, then one or 2 fans pulling the hot air out.....

Its what im doing. Works great.

[gadgetguy]

... If not you will have to blow the machine out on a regular basis.

This should be normal maintenance anyway.

[SingSing]

2 fans on the Front of the case pulling air in, then one or 2 fans pulling the hot air out.....

Its what im doing. Works great.

When you get it, you can do the job with one fan insteads of four. But there are nothing wrong with Your approach. since thermo-couples and flow meter, data logger and ... are not household items. Also, wire up four fans is less work than the detail thermo analysis.

[Marty2003]

... Well, long story short.. I had screwed
the fan on the wrong side -- Top was screwed in, Bottom'wise
And all the air (and dust) was being pulled into the fins.

Maybe I've been wrong all this time, but I'm pretty sure the CPU fan is supposed to be blowing onto the heatsink. That's how all my CPU/chipset fans have been attached, and they came pre-attached to the heatsink, I didn't screw them on the wrong way. Here's where I think ROF is wrong too. I used to hang out at a case modding site and I've always been told intake from the front and side and exhaust from the back and top. It just doesn't make sense to have a side fan blowing out if the CPU fan is blowing onto the CPU. Maybe it's just AMD systems, because that's all I've owned, but I'm pretty sure I'm right on this.

[Cobra]

If you have a side port you should exhaust the air out since your processor fan is usually close by blowing air that way anyways.

Don't processor fans blow on to the heatsink? If so, your side fan should blow on to the CPU cooler, otherwise they'll be competing for air.

[SingSing]

I'm pretty sure the CPU fan is supposed to be blowing onto the heatsink. That's how all my CPU/chipset fans have been attached, and they came pre-attached to the heatsink, I didn't screw them on the wrong way. Here's where I think ROF is wrong too. I used to hang out at a case modding site and I've always been told intake from the front and side and exhaust from the back and top.

You did the work, you are right on the subject.

[Super Warrior]

2 fans on the Front of the case pulling air in, then one or 2 fans pulling the hot air out.....

Agreed. Having a balance of fresh air coming in, and old air going out, is the way to go.

If he does not have enough spots for 4 fans, and maybe 3 instead. Then its best to have two fans drawing air in front, and the 3rd exhausting air-out in back. Giving positive air-flow, as more fresh air is going in than what is going out.

If only places for two fans, then its simply 1 intake-fan in front, and 1 exhaust-fan in back will do the job.

[Super Warrior]

When you get it, you can do the job with one fan insteads of four.

Perhaps but if you have at least two fan-slots available, theres no reason you can't just put two fans in. Easy to install and decent quality fans are cheap. 1 fan for intake on the front, and 1 fan for exhaust on the back is the minimum to ensure good airflow throughout the system.

**I highly recommend to anyone in this thread looking to buy a casefan, BUY ONE WITH AN ADJUSTABLE SPEED knob on it.**

This way you can freely adjust the fans for desired air flow/noise level.