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Old 04-06-11, 03:50 PM   #1
MN Renovator
Less usage=Cheaper bills
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Default 800CFM of air, how much power?

I was always curious why my electric bill in December and January was so much higher than my other months. I don't use much energy, mostly the refrigerator, electric clothes dryer, laptop, and climate control.

The refrigerator wasn't running more in a colder house, my electric clothes dryer is used about the same as any other month because I wash everything about the same rate and the number of loads per month are about the same. Laptop is never off because it doesn't use much power running and I'm almost always on it when I'm at home and its usually doing something for me anyway such as file serving or something else. ...but I'll get the point.

My extra power usage, which I always thought was from the furnace, really is using a heavy amount of power. Today I was curious about how much a blower uses on a furnace so I pulled out my clamp meter pulled the cover over the blower and did a little test.

I attached the picture of the ammeter. 6.26 amps after its been running for two minutes. The updates about twice a second, its initial startup draw that the meter read was 9.48 but since it doesn't update often enough I know that it was only within about the first second but have no real knowledge of the real peak. Usually motors have a peak draw of 3x what they run at. 3 seconds after its running its at a little above 6 amps and then goes up to 6.26 after about 15 seconds, what I assume is some pressure building in the ductwork.

Either way, I don't really get it because this motor is a 1/6 horsepower shaded pole motor, so for it to consume 1/6 horsepower electrically it should be 125 watts or so, add a little bit more for inefficiency and then we call it a day. ...or so I thought.

Turns out it is using a full horsepower. I'm pretty confident this is the source of my high electric bill in the winter but I didn't think its use was that much. The motor is lubricated and it takes a good deal of time to spin down when its shut off.

What do you guys think, is it expected for a furnace blower to use this much electricity? Not quite $10 on the bill but this thing runs much longer hours when its pushing air when cooling the house with the air conditioner. I'll be clamping my meter on the outdoor condenser too when summer comes around.

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