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Re: [AGA-Member] Small, quiet, large quieter, high velocity noisier, low velocity quieter fans

A few thoughts about fans, especially the tube-axial type
like computer case fans.

A fan's ability to cool hot items is purely a function of
how much air it moves in a given period of time. The tips
of the blades do 90% of the work, so a bigger diameter
means much more air moving, other things being equal. 

For a 3" fan to move as much air as a 4" fan it needs to
spin about 2-3 times as fast. It moves less air per
revolution so it has to move air at a higher velocity if
it's going to move the same volume of air in a given period
as a larger fan.

The faster a fan turns the louder it is. The higher the
velocity of the air, the louder the fan.

The other thing affect fan performance is the bearings.
Despite all the diff hype and names for bearing types,
there are basically two that are used: Sleeve bearings and
ball bearings. Sleeve bearings tend to be cheaper. They can
be quieter initially than ball bearings, but ball bearings
tend to wear better and those fans will remain quiter over
the long run, other things being equal. Cheap bearings of
any type won't wear well and won't be quiet.

A room fan is sometimes all one needs to hold down aquarium
temps, either to move heat away from the aquarium or to
move hot air out of a room with several aquaria. Room fans
are usually the cheapest and easiest, but not the quietest

One rarely sees figures for volume of air movement (cfm)
and noise (dBs) for fans unless one goes to the
manufacturer. Mouser.com sell several brands (high and
medium quality) and post specs in the catalogue and on-line
for many of the dozens and dozens of fans they sell. 

If you see remarkable specs for a fan from a manufacturer,
check how long they've been in business and how they are
regarded in the industry. Some of the fly-by-nights post
remarkable specs that defy the laws of physics and the fans
they sell are actually made by one of the other
long-standing companies, who would give much less
remarkable specs for the same fan.

Some of the big names in case fans are EBM/Pabst (a little
pricey but very high quality), Adda (your computer probably
has several of these inside regardless of the brand on the
label), Bi-sonic, Qualtek, and Orion. There are some
others; that's not a complete list.

Have plants, have fun,
Scott H.
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