how do i measue fans for the computer. (lol i know)

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seems stuipid but where do i measure the actuall fan.  a picture will
be very helpfull.  also will going a couple of days w/ out fans  hurt
my comp.   just bought a new video card and power supply and the
previous fans were sottered into the power supply.  the new power
supply has a big fan moving some air in the computer but not that

could you also reccomend some good case fans. thanks.  


Re: how do i measue fans for the computer. (lol i know)

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Example: an 80mm fan measures 8cms across its entire width.
These are the ones normally mounted in the case.
Fans depend on your budget, and what you want to use them
for. ie. general computer use or high speed gaming.

Re: how do i measue fans for the computer. (lol i know)

(korky122) wrote:

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That is like asking whether it is OK to run your car without
water in the radiator. You know it is not being cooled

One thing you can do, is take the side off the computer, and
take a large AC powered fan, and point it at the components
in the computer. That will provide a measure of cooling
until you get your computer case cooling fixed.

For help with fans, it is usually a good idea to tell us
what computer case you are using. If you have a URL to
the web page with a picture of the computer case, that
helps. Knowing the vintage of the computer (how old it
is) and the processor type, allows the estimation of
how much cooling might be needed. If you had a 35W
Pentium 3 processor, you might not need quite as much
cooling for the computer case, as you would with a
115W Pentium4.

A general recommendation, would be one intake fan in the
front of the computer case, and one exhaust fan. The fan
in the PSU doesn't count, because it is so slow. Some
computer cases have room to mount a fan down low, in the
front of the computer, and room for one more fan, just
below the PSU in the back of the computer. Air moves
from front to back in the case, so the front fan
pulls in, and the rear fan pushes out.

   CFM = 3.16 x Watts / (allowed temp rise deg F)

If you had a computer that dissipated 150W while gaming,
and you set the computer case air temperature rise to
10F (well cooled) or 13F (OK cooling), then the number
of cubic feet per minute would be 47.4 and 36.5 CFM
respectively. (Note - the "dissipated" number is the
real amount of power the computer uses, and it is _not_
your PSU watts rating. You can use a 450W power supply
on a computer that is only consuming 150W, and the fan
is selected for 150W of heat and not 450W!)

60 x 25.5 14.83CFM 36.0dBA FBL06A12H1A  <-- "H" equals High
60 x 25.5 13.06CFM 32.0dBA FBL06A12M1A  <-- "M" equals Medium
60 x 25.5 14.83CFM 29.0dBA FBL06A12L1A  <-- "L" equals Low

80 x 25.5 35.31CFM 42.0dBA FBL08A12U1A  <-- You can hear this "Ultra"
80 x 25.5 30.01CFM 39.0dBA FBL08A12H1A
80 x 25.5 24.71CFM 33.0dBA FBL08A12M1A  <-- Quiet enough
80 x 25.5 17.30CFM 26.0dBA FBL08A12L1A

92 x 25.5 54.72CFM 47.0dBA FBL09A12U1A
92 x 25.5 45.89CFM 40.0dBA FBL09A12H1A
92 x 25.5 45.9 CFM 40.0dBA FBL09A12H1BX <-- BX means fan speed monitoring
92 x 25.5 35.30CFM 36.0dBA FBL09A12M1A
92 x 25.5 31.77CFM 33.0dBA FBL09A12L1A

120 x 38  86.49CFM 48.0dBA FBL12G12U1A
120 x 38  81.19CFM 46.0dBA FBL12G12H1A
120 x 38  67.07CFM 41.0dBA FBL12G12M1A
120 x 38  52.95CFM 35.0dBA FBL12G12L1A

In the very first entry in the table above, the external
dimensions are 60mm x 60mm x 25.5mm. That means the fan
is one inch thick. The fan is square, and the 60mm is the
outer dimension.

To get our 47.4CFM, we could use a 92mm "ultra" fan, with a
47.0dBA noise level. Or we could use a 120mm "low" fan, with
a 35dBA noise level. Larger fans can be used for quieter
operation, but will only give their rated CFM, if there
is sufficient vent space to draw or push the air.

You'll need to measure the mounting place for the
fan, and see which size it uses. Most fans don't come
with a high, medium, low rating, but you should be able to
compare the CFM and the noise level to the table of Panaflo
fans above, to get some idea what catagory they fall into.

If you are getting one of the higher air volume fans,
a speed adjuster is handy. You can get multi-channel
controllers that fit into a disk drive bay, or one like
this can hang loose inside the computer:

I've used a 120x120x38 in one of my computers, and
even with a fan speed adjuster, it is still loud.

When one fan pushes in, and the other fan pushes out,
the CFMs don't add together. But the fans will get
closer to their rated CFMs if run that way. I don't
understand all the details, but there is a curve for
fans, where the CFMs drop as the air resistance of
the case increases. If you had a fan from a vacuum
cleaner, that can handle more pressure drop than
a computer cooling fan. Once a computer cooling
fan is mounted inside the computer case, the air
volume rating drops, depending on how restrictive the
vent holes are. My big fan didn't move that much air,
until I opened more vent space for it.

Also, fans come in two wire and three wire form. In each
case, there is a 1x3 tiny fan connector for the mobo. The
"BX" fan in the above table, has three wires and allows
the fan RPMs to be monitored. As you can see in the table,
the rest of them only have two wires. The same is true
when you shop for a case fan - a lot of them don't have
the RPM wire, so you won't see the RPMs listed by your
computer monitor chip. It is hard to find a good fan,
that also includes an RPM signal, for case cooling fans.
A CPU cooler is much more likely to have the RPM signal


Re: how do i measue fans for the computer. (lol i know)

korky122 wrote:

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Re: how do i measue fans for the computer. (lol i know)

korky122 wrote:
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Not without a processor fan you don't. Not unless you want to repace
the processor.

You can get away without the case fans for a while. How long will
depend on your processor and other components. If you MUST, open up the
case and put a big house fan blowing on the motherboard.

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Re: how do i measue fans for the computer. (lol i know)

On Tue, 02 May 2006 14:30:48 GMT, no@spam.invalid (korky122) wrote:

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If you are talking about actual size its pretty standard. Most of the
old ones used 80mm. A lot of the newer ones are starting to use HUGE
120mm fans like my new Antec. That way you can use less fans or run it
at lower rpm for less noise.

I did run into a one weird fan a 90mm or something fan on the MGE case
I bought.

Re: how do i measue fans for the computer. (lol i know)

On Wed, 03 May 2006 16:37:59 GMT, ""

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Compaq/Dell/HP (Gateway??) also commonly use 92mm rear
exhaust fans.

Re: how do i measue fans for the computer. (lol i know)

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Good to know. You know I cant even remember what my Compaq had. I
think it had very few fans since I cant remember taking any of them
out when I threw the case away.  It was a fairly cheapo plasticky
small cramped mid case.

Re: how do i measue fans for the computer. (lol i know)

On Thu, 04 May 2006 10:50:55 GMT, ""

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Yep, Compaq has for years been one of the main OEMs who
liked to use the PSU fan to cool the CPU 'sink or moving to
the chassis rear fan when heat levels were getting too high
to have a lower RPM PSU fan do the entire job.

Sadly some of Dell's fans in recent years tend to get a bit
noisey from wear, or it seems a bit of wear in conjunction
with the PWM control used by the motherboard.  Some (all?)
are ball-bearing fans too, so it's not just a matter of
relubing them.

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