I have an old squirrel cage fan from who knows where (a furnace at one point). Something like 12″ by 12″. is there any way to determine the CFM output. I realize that rotational speed must be figured in. If there was ever a label on the structure, it is gone.
-Paul
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Here I thought this was about my ex-wife's boots.
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Did you want to know the fans output or the actual velocity inside the duct?
Even if it did have a label on it, that would only give you a rating as length, size, & offsets in the duct will effect the actual cfm.
You can get a gauge like this one that will give you real numbers.
View Image
http://www.valuetesters.com/Extech-AN100-CFM-CMM-Digital-Thermo-Anemometer.php
And, really, the cfm is related to the heating calculations for the house, which set the number btuh to deliver. From the btuh one can then cipher the cfm per room. The per-room gives a duct & register sizing, which then defines the trunk sice back to the blower.
The returns are supposed to be sized similarly.
Sometimes.
Sales rep from the hvac outfit may or may not do that sort of thing (very much a milage may vary situation).
Too many cfm can be like putting a four-barrel carb on the lawn mower; too few like putting the mower's carb on your V8. (Oh, and there's a very real possibility that the ducts were never sized to any system, let alone the present one, too <sigh>.Occupational hazard of my occupation not being around (sorry Bubba)
CFM output that the fan is capable of in it's current state with the original pulleys. I'm intrested in trying this fan to push air down an 8" pipe. 6" side pipes attached by means of Wyes would go to planer and table saw. I'm hoping for a venturi effect to draw dust and then be pushed to a collection bin. I saw a similar setup at a sawmill. Of course if this dosn't work, I can always spent th extra and put a "normal" system in place.-Paul
I've helped build a couple of dust collection tables that used an old furnace squirrel cage & motor.
Most of the furnace stuff I've seen is in the 1750 rpm & 3/4 to 1hp motor which will not do what you are describing as you need a lot more velocity to create the venturi effect.
As I replied to Junkhound, I somewhat expected that answer. Ah well, back to the drawing board.I do have a 40" direct drive three blade fan (I think it has a 7 horse motor on it) that we had for a hay dryer. I know that pushes enough air but the electric meter spins like a top when you hit the switch.-Paul
..... in it's current state with the original pulleys...... saw a similar setup at a sawmill.
Believe this - Wont work with old furnace squirrell cage blower. The sawmill fan was much sturdier.
Actually have been there, tried that. Needed to speed up the squirrel cage fan (with 3 HP motor also) to get high enough velocity, at which point the blades on the squirrel cage bent all the heck outa shape and didnt blow nothin!
Welded up and balanced an 18" dia radial vane rotor that fit inside the old fan housing, that worked, 3 HP at 3550 RPM direct drive.
As I somewhat expected (but had hoped for the best). :-(