Can you put a rheostat on a whole house fan?

piedmontJune 26, 2007

After hearing people in my area raving about whole house fans I had a 36" 6900CFM one installed in my house which is the largest I could fit in my hallway, it was purchased at Home Depot. I didn't install it nor wire it. Turning it on low, sounds as loud as a Harley Davidson idling in my house and I later found out the size of my house needed only a 1000 CFM. We can't sleep with it on, and our 2 cats get the *#$! scared out of them and run around in a panic the entire time, which usually means running over us trying to sleep.

It's a fixed pulley on a motor using a belt to drive the fan blades. The switch has a High/Low/Off. I don't know if this applies but I intercept the wires going to the motor and put in I think it's called a dual pole single throw. I did that because in winter I cover it with insulation and had a friend ask, "What's this" and flicked the switch. After that disaster I put in that switch so it can't be turned on accidentally when I have insulation over it. Does it sound like a system I can replace the High/Low/Off switch with a special fan rheostat? Thanks

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Most of the fan rheostats I've seen are rated for light duty, such as for a fireplace blower fan. If you can find one that is the same current rating as the fan (or higher) it should work.

You might also want to call the fan manufacturer, tell them your problem, and see what they recommend.

    Bookmark   June 26, 2007 at 2:46PM
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This type of motor cannot be speed-controled with a rheostat. You would be much better off to get a smaller fan installed. Perhaps you can sell this one on e-bay.
Even with the current fan, the noise level might improve with improved vibration resistant mounting for the fan and motor (it may not be isolated from one of the houses framing members), better ventilation from the attic to the outside (the air has to go somewhere), and more open windows (the air has to come from somewhere). You might also look into getting a larger pulley for the fan and/or a smaller one for the motor.

    Bookmark   June 26, 2007 at 2:55PM
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Maybe a dumb question. If it can't be controlled with a rheostat how does the high/low switch allow it to have 2 speeds? Thank you

    Bookmark   June 26, 2007 at 3:10PM
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If the fan uses an induction motor, which is likely, I think a ceiling fan control may be able to handle it IF the control is up to the load your fan presents. Check the fan's nameplate and the control's rating. It sounds like a big'un, so I expect that you'll have a tough time finding a control with enough capacity.

Note also that you will probably void the warranty by operating it with a speed control. It may even be a code violation if the installation instructions state that a speed control should not be used.

    Bookmark   June 26, 2007 at 3:30PM
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Induction motor that can have speed varied are a relatively new and will be labeled as 'suitable for...'.
A regular induction motor will be damaged by a speed control.
Special cores and windings are required to use a conventional triac dimmer (or even an 'inductive dimmer') with an electric motor.

    Bookmark   June 28, 2007 at 9:07PM
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Brick, you're probably right, but I would argue that a motor whose windings are already tapped for speed control is pretty likely to survive the torture of a triac control. At least that's been my experience - but I'll admit my experience isn't exhaustive, and perhaps I should be wary of suggesting such things.

Regardless, it's likely to void the warranty.

    Bookmark   June 29, 2007 at 1:37AM
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Taps for speed controlling an induction motor normally play with the number of poles the stator winding has.

    Bookmark   June 29, 2007 at 8:17PM
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try increasing the size of the pulley on the fan end.. is a good place for pulleys.

otherwise a rheostat will not work.
the triac based speed controller will if its size for the the motor.

the other way would be to block some of the air flow.
since the fan is driven with a belt the motor the motor isn't cooled by the fan


    Bookmark   June 29, 2007 at 10:39PM
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Yes, solid state. I've used one for 20 years now on a 3/4HP permanent split capacitor induction motor driven whole house fan(came with it). has the lowest price or you can pay two to three times as much. These switches are widely available.

I had to join to post this. I have twenty eight years industrial I&E experience. These other answers were killing me.

Here is a link that might be useful: KB Electronics

    Bookmark   June 29, 2009 at 3:11PM
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