Cooling fans, can they be fitted either way round?

target7 · 18-06-2007, 05:31 PM

Hi all

First post and thanks for being there.

Something puzzles me and I feel sure someone here will solve the puzzle for me!!

If I use cooling fans to (a) draw warm air out of the case and (b) bring cooler air into the case - does this mean I have to fit fans different ways round to achieve each of those outcomes?

The only thing I notice when for example looking at an Antec 120mm fan I have which is in its original packing is the shape of the blades. When viewed in this way with the Antec circular logo facing me, the blades appear to curve backwards. Is this called concave? And, I imagine when this is fitted to the inside of the case, the logo will remain visible from outside the fan grille, and that the blades will curve backwards in the same way that they appear to me at present.

Perhaps they are all fitted in one way (like described above) and it has something to do with convection currents of the air within the case, and not which way round a fan is fitted to the case.

Be grateful to hear from those of you who know about such things please, as this has always concerned me and I would really like to understand this properly.

Many thanks.

RobertB · 18-06-2007, 05:44 PM

Yep, you'll need to alter the direction the fan points.

I draw in my air from the front & bottom, and out the back & top.

This way I don't suck in dust bunnies from the back and I can get rid of the hot air more easily (since it rises).

I "think" the side to which the blades curve back is where the air is drawn in. I couldn't remember when I built my most recent rig so I just tested them with my hand.

Not very technical, but it gets the job done.

Addis · 18-06-2007, 06:04 PM

For me, the side which has the power cable slotted into the plastic casing is the way which air leaves the fan.

Big B · 20-06-2007, 11:32 AM

You'll have to check the side of the fan, but they should have arrows indicating which way the blades rotate and which way the air is blown.

henry222 · 21-06-2007, 01:02 AM

It may seem obvious when you know...but you can fit them anywaya you like provided they obey two rules: correct supply, not fighting each other. If your psu is taking air out of the case (the most likely) then a side-fan should blow air In, otherwise you are sharing the available airflow.
There are issues about sucking in dust, but largely it's amatter of taste - if you suck or blow, somewhere else blows and sucks - the truth is that you should keep things clean, this was a concern in the days of Floppy drives which were open to the elements, but modern pcs have no "open" parts and dust only sticks "where the airflow is low", so it doesn't matter IMHO..
Turn off the PC if sweeping the floor etc. or when sanding the woodwork...makes sense, eh? to put a cover on the PC (or place in another room) when it's cold.
But keeping the thing running-cool is the most important issue, esp the processor, the video-card (if fancy) and the PSU (but they are usually self-sufficient.
FWIW My own PC has a low power need, so just the psu fan and the one on the processor...so I fitted one inside to blow about anything the others missed and being inside the noise-level would be small.
If your PC monitors Processor temperature then check the performance against room temp - and try reversing the fan (by turning it round). Do not reverse the electrical supply...fans are electronic controlled and won't take being operated by reverse polarity.
I'm not sure about the badges or blade shape as you describe...the direction of blow can be determined by powering it up, then mark it.
\
obey the rule that they mustn't fight each other - - - Larger fans are said to be quieter, for a given airflow. The important thing is to keep everything as cool as possible, so don't obstruct the grilles, or place near a heat-source etc.
Good luck.

18-06-2007, 05:31 PM	#1 (permalink) Top
target7 Geek Trainee Join Date: Jun 2007 Posts: 3 Status: Offline	Cooling fans, can they be fitted either way round? Hi all First post and thanks for being there. Something puzzles me and I feel sure someone here will solve the puzzle for me!! If I use cooling fans to (a) draw warm air out of the case and (b) bring cooler air into the case - does this mean I have to fit fans different ways round to achieve each of those outcomes? The only thing I notice when for example looking at an Antec 120mm fan I have which is in its original packing is the shape of the blades. When viewed in this way with the Antec circular logo facing me, the blades appear to curve backwards. Is this called concave? And, I imagine when this is fitted to the inside of the case, the logo will remain visible from outside the fan grille, and that the blades will curve backwards in the same way that they appear to me at present. Perhaps they are all fitted in one way (like described above) and it has something to do with convection currents of the air within the case, and not which way round a fan is fitted to the case. Be grateful to hear from those of you who know about such things please, as this has always concerned me and I would really like to understand this properly. Many thanks.

18-06-2007, 06:04 PM	#3 (permalink) Top
Addis The King Join Date: Jan 2004 Age: 18 Male Posts: 5,257 Times Helpful: 404 My Mood: Drunk Status: Offline My Computer	For me, the side which has the power cable slotted into the plastic casing is the way which air leaves the fan. __________________ Never trust a program you don't have the source code for. My website \| Powerful Desktop Linux \| Linux for human beings \| Linux for power users \| Linux for ricers

20-06-2007, 11:32 AM	#4 (permalink) Top
Big B HWF Godfather Join Date: Dec 2001 Age: 28 Male Posts: 9,673 Times Helpful: 585 My Mood: Devilish Status: Offline My Computer	You'll have to check the side of the fan, but they should have arrows indicating which way the blades rotate and which way the air is blown. __________________ Hardware Forums\|HWF Rules\|My DVD's\|PSU FAQ\|HWF Folding Team

21-06-2007, 01:02 AM	#5 (permalink) Top
henry222 Geek Trainee Join Date: Jun 2007 Gender: Male Posts: 43 Times Helpful: 5 Status: Offline	It may seem obvious when you know...but you can fit them anywaya you like provided they obey two rules: correct supply, not fighting each other. If your psu is taking air out of the case (the most likely) then a side-fan should blow air In, otherwise you are sharing the available airflow. There are issues about sucking in dust, but largely it's amatter of taste - if you suck or blow, somewhere else blows and sucks - the truth is that you should keep things clean, this was a concern in the days of Floppy drives which were open to the elements, but modern pcs have no "open" parts and dust only sticks "where the airflow is low", so it doesn't matter IMHO.. Turn off the PC if sweeping the floor etc. or when sanding the woodwork...makes sense, eh? to put a cover on the PC (or place in another room) when it's cold. But keeping the thing running-cool is the most important issue, esp the processor, the video-card (if fancy) and the PSU (but they are usually self-sufficient. FWIW My own PC has a low power need, so just the psu fan and the one on the processor...so I fitted one inside to blow about anything the others missed and being inside the noise-level would be small. If your PC monitors Processor temperature then check the performance against room temp - and try reversing the fan (by turning it round). Do not reverse the electrical supply...fans are electronic controlled and won't take being operated by reverse polarity. I'm not sure about the badges or blade shape as you describe...the direction of blow can be determined by powering it up, then mark it. \ obey the rule that they mustn't fight each other - - - Larger fans are said to be quieter, for a given airflow. The important thing is to keep everything as cool as possible, so don't obstruct the grilles, or place near a heat-source etc. Good luck. Last edited by henry222; 21-06-2007 at 01:09 AM. Reason: tidying

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18-06-2007, 05:44 PM	#2 (permalink) Top
RobertB Geek Trainee Join Date: Aug 2006 Posts: 16 Status: Offline	Yep, you'll need to alter the direction the fan points. I draw in my air from the front & bottom, and out the back & top. This way I don't suck in dust bunnies from the back and I can get rid of the hot air more easily (since it rises). I "think" the side to which the blades curve back is where the air is drawn in. I couldn't remember when I built my most recent rig so I just tested them with my hand. Not very technical, but it gets the job done.

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