"dpb" wrote in message
...
On 7/11/2013 8:49 AM, Ecnerwal wrote:
In ,
wrote:

Are they open-flow or is there air blockage via a damper system or
discharge/intake louvers or the like? That could drastically
raise the
flow restriction and raise motor loading if designed/sized solely
for
open unrestricted flow...

Careful with the assumption here - many fans draw _less_ current
"restricted" since they move less air, so they are doing less work.
Counter-intuitive, but often true. Toss on a meter and try it. I
think
it was Bruce who mentioned that many people kill furnace blowers by
"unrestricting" ductwork to the point that the motors overload...

Depends on whether the restriction raises head pressure
significantly...

Really on if the blades have stalled.