On 10 Apr 2005 05:25:18 -0700, wrote:

Another key consideration is warranty and repair cost. I've seen many
reports that indicate that variable speed DC motors are prone to much
more frequent failure. There is not only the motor but the power
control circuitry that can fail and to replace either costs a lot more
than a std motor.

Exactly why we opted for the regular continuous fan instead of the
variable; cheaper all around, and the energy savings from the variable
speed wasn't worth the risk of failure and subsequent
repair/replacement costs.