"dpb" wrote in message
...
On 7/11/2013 12:22 PM, Jim Wilkins wrote:
Just checked with a Kill-A-Watt. A muffin-sized centrifugal blower
draws 24W open, 18W with either the intake or exhaust blocked.

OK, let's recast what I was driving at...you're saying there's no
fan curve/as-shipped design point for which it's possible the OP has
done something to his ducting or louvers or the like that can result
in raising motor load above design so he shouldn't/needn't consider
that as a possible root cause/factor?

You said that, not me. I posted only the free-flow and fully blocked
readings for a small impedance-protected motor that doesn't represent
the loading curve of a larger one. The shape of the blades strongly
affects the pressure the fan can produce and the full-load power.
You'd need a wattmeter and a gage like this:
http://www.dwyer-inst.com/Product/Pr...ges/Series2000
to determine the conditions of that specific installation. I've done
it for the cooling fan for vacuum tube and solid-state radio
transmitters, not for HVAC.
jsw