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I have a ceiling fan on our bedroom's vaulted ceiling. Since we don't want 7' pull-cords, the speed is stuck at full-tilt, which is no good. The fan has separate switches on the wall for lights and fan on/off, though, so I tried putting a dimmer switch on the fan. Can that do any damage to the fan's motor, or is there anything else I'm not thinking of that could be a problem? I've noticed the fan makes a little bit of a groaning noise when I have the rheostat down, but since I've never heard the fan at slow speeds, maybe that's normal.

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If possible, try to find your fan's manual (paper or online). It's usually written in it. I know one of my fan asked for a specific dimmer model. – Maxime Morin Feb 19 '13 at 3:05
up vote 11 down vote accepted

Check the fine print

To find out if the dimmer can work with the fan, you'll have to inspect the dimmer. For this, you'll have to remove the cover plate and possibly pull the switch out of the box (in which case, make sure you shut off the power at the breaker). If you see the text "For Incandescent Only"; or something similar, you should not use this dimmer with a motor load.

enter image description here

Using a standard dimmer with a ceiling fan can damage the motor, and/or cause the dimmer and/or motor to overheat and cause a fire.

There are a few better options available to you.

Install a fan control switch

There are many different fan control switches available; with a wide range of styles and functions, you should have no problem finding just what you want. A simple control like this 3 speed fan control, will run you about 20 bucks, and installs using the existing wiring.

3 speed fan control

Install a remote control

If you're up for a bit more wiring, there are universal remote control kits available. You'll have to wire the receiver into the fan housing, so it's a bit more complicated than installing the wall control. But once the receiver is installed, you can place the wireless remote anywhere you like. There are a ton of these things available, so you shouldn't have any trouble finding one you like. You can even get a cool touch screen control, if that's what suits your fancy.

Touch screen remote

Install a new fan

If installing a new fan is an option, you could simply select one that comes with a remote control.

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My switch is this model, whose spec sheet online lists "Ceiling fans" under "Direct load type compatibility". So it sounds like I'm in the clear? – Dov Feb 21 '13 at 19:00
@dov The Spec sheet does indeed list ceiling fans in the "Direct load type compatibility" section, however, this is the feature list for the Diva® product line. Make sure you check the documentation and labeling on your specific device. – Tester101 Feb 21 '13 at 19:11
Ah, from the instruction pamphlet: "CAUTION: Use only with permanently-installed 120V~ halogen or incandescent fixtures. To avoid overheating and possible damage to other equipment, do not use to control receptacles, fluorescent lighting fixtures, motor-driven appliances, or transformer-supplied appliances." Thank you very much for helping me not to burn down my house! – Dov Feb 22 '13 at 1:05

Common AC electric motors have a high impedance on starting because velocity is 0, This draws a large initial current to get the motion started and as velocity increases impedance drops and the current draw decreases.

A dimmer will reduce the wattage to the fan motor meaning that you are increasing the impedance over time, meaning that heat will buildup until it becomes a potential fire hazard. This is the same reason that you shouldn't use a normal dimmer switch for incandescent bulbs as they have a large initial current draw.

In other words, don't do it. They make smart switches that can sometimes do this in a safer way.

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I don't know but I suspect a dimmer is a bad idea, but you can get 3 speed fan controls that are designed for this purpose. For instance this one.

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Under powering can certainly damage electronics, including motors.

It's possible, though, that your fan might be fine.

I would look for a fan designed to be used with a dimmer, find out what kind of dimmer it needs. Alternatively, many fans have their own integrated speed controllers.

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It's possible, though, that your fan might catch fire. – Skaperen Feb 19 '13 at 6:59

I know this is an old forum posting but thought I'd add to this topic with my experiences.

I'm no expert on this but I tried putting a 3-way fan switch on an older fan kit only to hear a non comforting noise coming from the fan motor after speaking to an expert I was told that the older fan's and motors weren't designed for those type of switches and would burn the motor up.

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Most bathroom ceiling vent fans are shaded pole motors and will not draw current anything like an AC three phase motor. Maybe search shaded pole motors and dimmer switches.

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This does not answer the question. – Tester101 Sep 10 '14 at 17:12

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