In article , dpb 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...

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