re: Updated: Should fans suck or blow?

This is not neccacarily true that you shouldnt have a fan sucking air but my heatsink has 1 fan blowing air through it and another sucking air out of it... so therefore none of what anyone has said is true!

re: Updated: Should fans suck or blow?

Re PZ Politics, yes Paul we do. Makes as much sense as someone trying to explain logical block addressing after sinking a few cold ones.
How come we allow people that we wouldn't buy a used PC from to govern a country?

(Now THERE'S a question and a half Mike. Remember the old saying, it doesn't matter who you vote for, a politician always gets in. -PZ)

re: Updated: Should fans suck or blow?

Isn't it time this subject was closed? The 6 years of comment have probably generated enough hot air themselves to contribute significantly to global warming.

(Sorry Mike. For a minute there I thought you were talking about Australian politics. I imagine you get your fair share of coverage over in NZ. -PZ)

re: Updated: Should fans suck or blow?

Fans dont really cool anything, they just draw outside ambient air in to displace the warm air inside the case, and the rear fan exhausts it.
As to should fans suck or blow, go and sit behind a pedstal fan and see if you feel cooler.
And in many cases it depends on the type of application.
Frank.

re: Updated: Should fans suck or blow?

Government Sucks, Tax Sucks, Fans move air, so set your intake fans to move the coolest air over the hottest components and your exhaust fans to smoothly remove the hot air from the case. Job done. Simple!

re: Updated: Should fans suck or blow?

Hi,
I have actually worked on this quandary, The answer is this■ considering the CPU is fixed to a motherboard and surrounded by other components that also generate heat it would be more beneficial to the CPU to blow cooler air down towards the motherboard, thus blowing away any harmful warm air created by other components, if it were to suck, it would actually draw heat towards the CPU from other components on the motherboard.
The best way you can help to cool your computer down is to introduce a third fan! (some computers already have them) not forgetting the power supply fan, mainly fitted inside the back or at the bottom front, the idea of this is to draw all warm air out of the case. On some ■gamer■ computers there is a fan fitted to the side of the case (inside) this is to assist the CPU fan and blow cooler air over the heat-sink.

Regards John.

re: Updated: Should fans suck or blow?

Surely the way to resolve this question is to run a test. 1. Run PC with fan blowing - Check temperatures. 2. Same again with fan sucking. I did own a PC where the CPU heatsink had a fan that sucked. It was provided with its own air escape channel to the outside, thus isolating it from the rest of the case. Worked fine.

re: Updated: Should fans suck or blow?

OK here we go again.
I am discounting all other influences such as heat radiation etc. in this
First of all, Fans don't cool - they only move air. What does the cooling is replacing the hot air in the cabinet with cooler air. just that simple.
Your heat sinks are radiative devices. They take heat produced by electrical devices and transmit it to the local environment - inside the case.
Your fan (Which by mechanical action actually ADDS heat to the air) moves that heated air either by pulling or pushing it out of the cabinet thus allowing the cooler outside air to replace it.
This means that the cooling is dependant upon the temperature differential between the air coming in to the case and the air inside the case. The closer they are in temperature, the less cooling there will be. There are other factors such as air mass and air density involved. The quicker you move that air the less time it has to heat from the internal radiation and the more heat can be removed - up to a limit.
If you have trouble understanding this, as yourself
"Why does a fan in an oven not Cool the food?"
Now, hOW you get the air to move is up to you.
I still advocate positive venting; our cabinets dissipate kilowatts of heat via this method but you do what you wish.

(Thanks Mike. There's a lot of sense in what you say. But you'll never convince some people. -PZ)

re: Updated: Should fans suck or blow?

G'day,
Guess I'm the one T O'S refers to in terms of positive pressure ventilation.

However..... to directly address the CPU fan question, I'll be the devil's advocate again!

Blowing dirty air onto a CPU heatsink is a *bad* idea. The fins soon load up with dust and detritus and rapidly lose their heat exchanging efficiency. Unfortunately, this also blows hot air and dust onto motherboard components, including memory slots and electrolytic capacitors.

From an engineering stand point, it makes far more sense to draw air over the relatively cool motherboard, up through the heatsink fins, and blow the resulting hot air AWAY from the motherboard. I dare you to say it ain't so!!

Norm, VK3XCI

(Yes, but where does that air come from Norm? Any moving air must have some contaminants in it surely? That's why some people go to so much trouble filtering the air that comes INTO their PC. 73's -PZ)

re: Updated: Should fans suck or blow?

Sounds OK to me Matt. You really should mount the fan on rubber blocks inside the case. The blocks should be like automobile engine mounts i.e with the screw or nut on one side of the rubber block not connected to that on the other side. That way the vibration and noise from the fan can't travel down a continuous line of metal (thread) to the body of the case. The pressure loss could be because the fan is trying to suck air through a blocked case grille or just because the grille itself causes some restriction, Setting the fan on rubber mounts in the case should allow some air to come into the fan from the sides of the fan as well and although this will not mean maximumum air into the front of the case it could be ok for your needs. Try it and see. I have no idea idea where you would get the blocks but maybe a computer or hobby type shop would have them.

re: Updated: Should fans suck or blow?

OK so im going to install my fans 2nite. I bought 2 Thermaltake Smart Fans. One for Intake and one for taking out air. The intake fan will be inside the case. So it wont be sucking up any new dust. I have a front grill to screw my fan onto but when i do i lose heaps of fan pressure and the fan gets louder. Im thinking of putting spacers/washers inbetween the grill and the fan. has anyone else done this?

(Hi Matt. I'd show that system to a friend and talk him/her through what you're going to do. From your description something sounds very wrong. Almost as though you're trying to suck air through solid metal. One fan working well - either in or out of the case - is better than two not working well. -PZ)

re: Updated: Should fans suck or blow?

My system cooling:
1x 120mm Front Intake Fan
2x 80mm Side Intake Fans
1x 80mm Top Exhaust Fan
1x 120mm Rear Exhaust Fan.

The olny problem I have is that the rear runs at 3500rpm moving 90cfm of air. VERY NOISY!!!

re: Updated: Should fans suck or blow?

well i think i have a diffrent kind of system.
i have standard fans and heat syncs on my cpu 2.8 prescot and gpu nvidia 6800 gt, my case is of a standard size, it has a small open vent at bottom front.
it has 1top fan sucking out, 1 side fan sucking out, i was reaching temps of 105 degrees in the bios reading not good, so i cleand it out took the heatsink apart removed a tonne of dust, then tried some new silicon gel on the chip, put it all back together etc, then i noticed my case had screw holes for a fan on mesh below where the psu(2 fan model.) sits put in a new fan that sucked out as well, and the temp has now droped from 31 degrees for mboard and 60 for cpu, this is a massive temp drop and the draw on the front vent is great.
the reason for this is:
negative pressure inside the case, if all the air is being sucked out of the case then it has to be replaced from somewhere, that is from of course the front vent, and the more suck you have the more air is drawn through.
thats physics.

re: Updated: Should fans suck or blow?

The way I have seen things air pressure If outwards will increase flow. Have a cut wire mesh area on the top of your case. This gives it a really good way to breath. So it can send the hot air out and pull in the colder outside air. Just with my 2 fans I get amazing results with my overclocked at 3.2 gighrz runs at 35C. Starting at 1.8 stock id say 95F is pretty good!

re: Updated: Should fans suck or blow?

Do you really need a case with a vented side panel with an 80mm fan?????

re: Updated: Should fans suck or blow?

Paul, Terry, I'm SO sorry to do this to you, but...

What if there were no fans? Of course, you would need a CPU fan and you need to design your system well and keep an eye on it to have it running ok with no case fans, but how will the system perform? Would you get more or less dust compared to in-fans and out-fans? How about if you maintained the case more often in terms of dust build up?

(Terry would always have fans because he's such a good tech writer. -Paul Zucker)

re: Should fans suck or blow?

two fans should hit air on the mother board to keep it cool and the heat released by the processor,heat sinketc.that hot air should be sucked out by two rear fans to keep it cool.it works i have done this and it works,since i keep downloading movies from the net, i had to make these changes.or the best solution is put a air conditioner.

re: Should fans suck or blow?

Fans should *never* suck air in--especially exhaust fans. The fan entryway into your case is the worst way to get cool air in because it will attract and ionize the dust coming in. Most cases have at least a filter or a design to deal with airlfow and incoming pollutants. Fans do nothing more than move air from one place to the next, and in the worst case, ionizing the dust particles to go settle in on all your internal components.

re: Should fans suck or blow?

Try looking at the other fans I've found the best way is to have the back fan (near the top) blowing while the front which is near the top sucking air in. I Think when you look at the cpu fan it might be better to have the CPU sucking in with this setup since in theory the hot air would be blown out. It keeps an AMD Athlon 3000+ at around 45 degrees on average (very good considering AMDs get considerable hotter than Intel chips hot, say 60 Degrees normally). My friends say "it's too cold" haha) Then Again, I do have 4 fans (adding an extra fan recently) if you include the CPU Fan. What do you all think?

re: Should fans suck or blow?

I believe the VERY best solution is to have a 'filtered fan' at the bottom of the tower blowing cool air in, with another fan at the top of the case, maybe the power supply, blowing out. This means that the air will properly circulate through the case and follows the law of physics in that hot air rises. As for heat sinks on processors etc., the fans should blow onto the heatsinks. Happy air control!

re: Should fans suck or blow?

I think you should have a look at the way your pc case is designed. most cases have a fan vent on the back that wil fit up to a 12cm fan. I personaly run my fans so as to suck all the hot air out of my case and the cpu fan to blow cold air onto the cpu. as mentioned before hot air rises so it make seince to have a fan at the bottom to blow air into your case and a high powered fan at the top to blow the hot air and the dust out or one at the front blowing in and one at the back blowing out even if you have a high powered fan blowing the air out its natural for most of the dust that gets draged in and cracks to be sucked out by that fan so unless your running more then one fan i believe they should always blow out of the case so as to keep it clean. I have had many computers come to me that have crashed but once opened and clean they work fine so keep in mind that dust is one of the biggest killers for your pc as is overclocking your cpu. There for if you dont overclock your pc and leave it the way it is ment to be then you should really need any more fans but if you wish to add a few more then keep them blowing out.

re: Should fans suck or blow?

You should always have more fans expelling air from your case then sucking air in.

Eg. Two 120mm fans expelling air at the back
and one 80mm fan at the front, refreshing.
This prevents the already warm air in the case being recycled again and again

re: Should fans suck or blow?

I agree with Mike P. fans should blow the air into the case so that the dust is not sucked into the case. In all wellbuild professional equipment that I have worked with while in the RAAF and various departments, all the equipment had fans that blew the air into the case and had filters on the fans that had to be cleaned every few hundred hours of use, if the filter is not cleaned regularly than the filter will clog up and reduce the airflow causing overheating of the equipment.
But as the normal domestic user normally does not, or forgets to clean filters, domestic computer manufacturers have opted for the easy way out by sucking air into the case through the various vents in the case hoping the dust does not settle in the case.

re: Should fans suck or blow?

It's not a matter of should they or not. If you look at the blades you will see that there is a curve in the surface of the blade. It has a trailing and a leading edge. When a blade is rotating in the correct direction the concaved side of the blade will be rotating into it's rotation direction and the convex side of the blade will be following. Most fans have an arrow to indicate it's direction of rotation. The only question is which way do you want the air to be moved and then you install the fan accordingly, eg mounted one way will push, turn it around and it will pull. The choice is yours. Remember to hook up the wiring as supplied as the motor has also as an integeral part of it's design a thrust side and if this is interfered with it will eventually damage the motor. Hint:: If you have a household fan,you know the one you switch on when it's hot look at the construction of it and you will get the drift.
Roger D

re: Should fans suck or blow?

My suggestion is a lot like MikeP in that you need to have positive pressure to keep out dust etc. That works well for cabinets or larger installations but it's a little inpractical for normal PC use. Many internal fans need to be able to blow cool air onto heat fins so you need a fan near the bottom, sucking in cool air, preferably through a good air filter. That pressurises the case as well but you need to let or force the hot air out - most important. Either a good opening or a outward blowing fan at the top. Make it slightly smaller and keep that pressure up. By the way, they're all the same, just turn them around to do what needs to be done.

re: Should fans suck or blow?

Fans neither suck or blow they just move air in 1 direction. You use this to get the best circulation over the parts that generate heat and remove this heated air from the case, it doesent matter if the air is pushed or pulled through the case

re: Should fans suck or blow?

The most efficient airflow would be found using 3 sets of fans,
* SIDE PANEL FAN - Set this to suck air into the case to help in ventilation,
* CPU FAN - Set this to blow air into the heatsink, as the side panel fan will be providing fresh air straight to this fan, allowing maximum cooling
* PCI EXHAUST FAN - Place a PCI exhast fan which will suck all air out, increasing overall ventilation and reducing the amount of hot air buildup. This fan will also allow some cooling for the other PCI devices around it and even ur AGP card if well positioned

re: Should fans suck or blow?

My old box has 2x40mm fans blowing air over the H/D and 1x 80mm fan at the back of the box down the bottom sucking out the hot air.
This system has worked well for me for 10 years plus it helps keep the dust down.

re: Should fans suck or blow?

Case fans should suck in from the front and blow out if they're on the back.

As for heat sinks, the short answer is, someone has tried it and I guess it was not nearly as good. The long answer is basically what reply 4 said, that you can't suck from a particular direction, only blowing works that way. So a heat sink fan will suck equally from the sides as well as in front of the heat sink, and you'll probably get dead zones right in front of the fan and on top of the chip where air is hardly moving at all, not a good situation. You'd need to do some aerodynamics to work it out though.

If you blow, you can direct it straight onto the chip.

============
Reply 1: You'll only get a tiny rise in pressure inside the case before the air starts forcing its way out of gaps--they're not particularly air tight, and you won't get any heating from the extra pressure. You'll also reduce the efficiency of the case fans.

re: Should fans suck or blow?

Most well made cases have fan slots at the back and on the side of the case. One slot is normally higher - usually the back one and another lower - side one is normally in the middle of panel and thus it makes sens to have one fan blowing air in from the lower side slot and the other sucking air out at the higher rear slot.

re: Should fans suck or blow?

MikeP on the above post is absolutely correct. Although with my PC, I have 2 fans on the front bottom of the case sucking air into the case and 2 slower fans on the back sucking air out. This provides positive airflow while maintaining pressure inside the case.

All fan installations which suck air into the case should be filtered ! I have seen so many cases with so much dust flith on the inside, I'm always surprised how long they last.

Please also note the important of not have dust and dirt inside your PC is that the dust and dirt can become statically charged also. This can cause big big problems.

re: Should fans suck or blow?

Check out you'r Physics(Boyle's Law / Charles Law) If you force air into a chamber you increase it's pressure and it's Temperature. If you suck the air out you have a drop in pressure inside the chamber and a drop in Temperature.

Best Regards Malc..

re: Should fans suck or blow?

The case fan should suck the air out of the case allowing the lower temperature outside air in. Re-circulating hot air inside a sytem will only create a higher temperature.
The CPU fan should allso draw the air through the cooling fins not force it through. (Its not a car radiator)
Forcing it through the heatsink increases the pressure under the fan but reduces the effective airflow.
Make sure that the entire area above the fan heatsink is clear of cables, as this can allso reduce the air flow of the fan.

99% of condensing units on air conditioners work this way. (The outside box with the big fan)
and if your scared of dust getting into the system just use an arcrilic filter. (The only way to completly seal a case would be with a tube of silicon mastic.) :)

re: Should fans suck or blow?

I have to agree with what Julian says. Hot air rises so when I decided how to have the fan setup in mine I have two fans in the front of the tower which suck air in, two fans in the side panel of the tower which suck air in (both sets of fans are at the lowest possible point). I have two more fans in the tower which expel air. Both of them are high up in the tower (one on the top and one just underneath the PSU). The CPU fan blows onto the (copper) heatsink to disperse the hot air. As a result the maximum temperature I can get my Athlon 64 3800+ to run at is 41 degrees while the lowest temperature I have seen is 23 (bios readings - not software readings).

re: Should fans suck or blow?

Yeah, fans should take air away from the CPU. But a case fan, i fell, is best just keeping a fresh cycle of air, in the front and out the back. That way the fan at the back (presumably the most powerful) will suck all the warm air out.

Wayne

re: Should fans suck or blow?

A general rule i stick by is that for every 2 fans blowing, there should be one sucking. and the sucking ones should be at the front/bottom.

re: Should fans suck or blow?

MikePPosted: 08/09/2005
The objective is to have the air pressure inside the case slightly above the normal air pressure.

Blimey more Micks posting here than a Catholic Boys School! LOL

I agree with this Mick in pressurising the cabinet.

Many years ago whilst travelling in Central Australia our car sucked in tons of fine dust through what we thought to be good door seals.

On talking to a tour coach operator he explained that the coach luggage bins had fans to keep the internal pressure slightly above the outside air pressure. This did stop the fine dust entering the bins.
Same principal with a computer box also. IMHO

re: Should fans suck or blow?

This wisdom comes from years of maintaining computers in hot, dusty environments. such as General Stores in Outback villages, and and Radar installations on airfields!

1. Positive pressure ventilation is "a good thing". Draw lots of outside air through a filter into the case. Exhaust it via the power supply and perhaps one other fan.

2. Negative pressure ventilation is "a bad thing". Blowing air out of the case sucks dust and detrius through every little crack, including floppy drives (remember them?) and optical drives.

3. CPU fans... look at the mother board. If the CPU fan blows down through the heatsink there is probably dust and debris sprayed all over the mobo, (including the RAM sockets), where the air exits the fins on the heatsink. This is "a bad thing". Depending on the airflow within the case, if the CPU is near the power supply, warm air bing drawn into the psu by the exhaust fan passes over the cpu, to be drawn down to cool it and then blow hot air over the mobo, again includin the RAM. Another "bad thing".

Summary.
Use positve pressure ventilation with a high volume of fitered air, baffled to pass over the mobo if required.
Suck this air through the cpu heatsink and blow it upwards away from the other components.

Works for me under conditions which a PC was probably never intended to operate.

Norm, VK2XCI

re: Should fans suck or blow?

I have a slowed down 12cm fan at the front SUCKING lots of air INTO the case; high volume at low speed! At the back, near the CPU, another fan 8cm SUCKS hot air out of the case. These 2fans cause a huge draft across the inside of the case drawing away most heat.

The PSU fan also draws air out of the case past its components. But best of all, I have a duct from the CPU fan direct to the exterior, where much colder air is drawn in and blown onto the heatsink! Works a treat!

Suck or Blow?... depends on your point of reference!
Airflow is everything!
Cheers
Bert

re: Should fans suck or blow?

my cpu fan blows onto the heatsink. my case fan at the front sucks air in through the mesh at the front, and my fan at the back suack air out of the case, this way the air is constantly being passed through.

re: Should fans suck or blow?

When it comes to Heatsinks - fans should blow into the heatsink to force the hot air out of the fins. However, when it comes to the case, the fans should extract air to take the hot air out of the case. This is because the hardware creates heat while running. If you just feed the case full of air, the compressed air will heat, and will not cool the components (which is opposed to what you are trying to achieve). When there is a lack of heat, the components will be forced to cool.

re: Should fans suck or blow?

your computer fan should be blow and must be compare volts not like higher or lower .. i dont want see your computer turn into pizza!! huh?

go buy good fan to make chip cool down !! all the best for your help .. we are help you computer people problem

congratution Paul you are Ace

re: Should fans suck or blow?

For tower cases I always have the bottom vent expelling air from the case.

This vent is closest to the floor (or desk top) where the dust is, and I have found that having this fan blow air out of the case reduces dust build up significantly.

re: Should fans suck or blow?

Blow. Have you ever tried sucking air across hot food to cool it, NO, you blow on it. The reason, I believe as to why fans blow on heatsinks is because by blowing, it can direct air more efficiently and penetrate into all the little nooks and crannies to disperse the heat more effectively. In order for sucking to be this efficient you would require some type of shroud around the heatsink so that the air would be drawn up through the entire heatsink rather than just sucking in from the sides.

re: Should fans suck or blow?

I work on the design of server and data-coms cabinets; this is my opinion on heat and airflow design
All PC cases should have fans that either suck air in through filters or blow air in through filters. The air should be permitted to exhaust under pressure.
The objective is to have the air pressure inside the case slightly above the normal air pressure. This is known as positive venting; it prevents dust and contaminates getting into the case through joins in the covers or vent slots.
If fans suck air out dust will be drawn in through any unsealed joints because the air pressure inside will drop. Air always moves towards the area of lowest pressure. Hot air rises. The coldest air is usually low down therefore it makes sense to make use of natural convection in airflow design.
My choice would be an external filter (for ease of cleaning) with two high volume fans on the inside providing redundancy, drawing air in through the filter at the bottom of the cabinet. A primary vent would be at the rear just above the CPU height with a single low volume exhaust fan (to maintain the internal pressure and to draw air over the CPU) and the transformer fan at the top being a secondary vent. Leave at least a hands width between the exhaust vent and the wall.
On the subject of dust, I would never advocate standing the PC on the floor, especially a carpet. If you can■t put it on a desk, at least keep it off the floor.

re: Should fans suck or blow?

I think it's obvious. Warm air rises so why shouldn't the fan HELP by sucking the air away from the CPU!?

I suppose it really stems as to how many other fans you have in your case and which way they are blowing.

There's no use having a case fan suck air into a case and a CPU fan sucking air FROM the CPU when they both face each other, know what I mean? You have to consider air flow.

Regards

Julian