Question about fan control

[smash]

I have a 172mm comair rotron fan. Its rated at 12v-2.26 amps
I would like to have variable fan control. My question is
what kind of pot or rheostat to use?
The most common ones are 5watt and 25 watt, and if my math
is correct my fan is at 25watts already. From watt I hear turning down the power increases the watts? So a 25w pot or rheo would be at max from the start. The other thing is that when the power is turned down they heat up.
In a plastic box this could get ugly!!

If I'm wrong let me know. any and all suggestion are appreciated

[flounder43]

My 5 watt rheostat works fine with my 4.6 watt 120mm fan.

[Veland]

I'm no expert, but AFAIK the watt rating must match the maximum power of you fan. 2,26 A should turn out like about 26W, so 25W reostat is a bit small. Also as the fan slows down, it need more amp and you end up with a higher Watt drawn. There are other discusions where people who actually know what they're talking about give formulas for calculating Watt rating and Ohm, so search for them for some good info.

But reostats at 30+ W are expensive..

[WyrmMaster]

The other option to to use a switch and switch from 12 to 7 volts. Not as much control, but you dont have the heat problem.