Automating Fan Control--Don't Use a Light Dimmer!

Continuing the discussion from Fan Light Dimming - Aeon Labs Aeotec Z-Wave Micro Dimmer:

Thanks for the shout. Yeah, basically you need to read the manufacturer’s directions for the fan, and check that against the manufacturer’s directions for the dim control.

Rate controls For home use are usually either TRIAC or VFD (Variable frequency drive). A TRIAC controller varies only the voltage. This is what’s typically used for a dimmer light because that’s exactly how you make the light brighter, you give it more voltage.

A VFD varies both the voltage and frequency.

But more importantly in this context, is how the dimmer knows to turn itself on. The short answer is the dimmer switch itself, if it uses a TRIAC, is very sensitive to changes in the voltage, and basically it can get confused and send the wrong amount of current at the wrong time. This is what’s responsible for flickers. The problem is that kind of “flickering” in a fan motor control can cause the motor to overheat.

Most of the time, it’s just not a good idea to use a dimmer intended for light switch as a motor control. There are almost always warnings on both the dimmer switch and the motorized device install guides.

There are variable speed controls that are made specifically for fans or other motorize devices… Sometimes they are using a TRIAC switch, but they include other circuits which control the actual amount of voltage sent. There are different ways to do this but they’re all designed to keep the motor safe from variations in the TRIAC distribution. However as you undoubtedly noticed when you start looking around, these type of controls are more expensive, and usually, noticeably bigger than the light switch dimmers. So I know it’s tempting to just grab a light switch dimmer instead, but it’s probably not to code, and it’s probably not safe.

None of this has anything to do with Zwave or zigbee or network protocols. Or SmartThings. It just has to do with the part of the switch that controls the current to the fan. It’s possible to use a networked relay to send current to a VFD switch which then controls the fan and still maintains safe control. So a lot depends on the exact wiring set up.

Which is also why it may be possible to do something with just the light portion of a fan that also has an independent light. It just all comes down to the details.

What Wall Switches are Available for Variable Fan Control? (That won’t burn down the house)

There are at least two Zwave wall switches that are specifically made for variable speed control for fans, one from GE and one from Leviton. Both are on the official “works with SmartThings” list, so that’s a good place to start. See the forum for more discussion of each.

The Leviton:

I don’t like the look of rocker switches–what else can I use if I just want to toggle on/off?

If you just want a toggle switch, you can use the SmartenIT zigbee relay (also on the “works with SmartThings” list) with most fans. That lets you use any switch you like (the relay installs inside the switch box). Again, check the ratings for your specific fan motor.

Or you can use any other networked toggle switch that is rated to match the specs of your fan motor. Again, read specs carefully.

What if I want to also control the light that’s in the fan fixture?

If you want to control the fan’s light separately you usually have three choices: either set up two separate wall switches, or use a two button switch, or, if the light is the kind that works with a pull cord, install a light control relay inside the fan fixture to control the light, and use one of the methods we’ve already discussed to control the fan. Please make sure you know what you’re doing if you’re trying this approach, the wiring can get tricky.

For further discussion of options for controlling both the fan speed and the fan’s Lights, see the following FAQ (it mentions Alexa in the topic title, but applies whether you are using a voice assistant or not:

For discussion of using a micro switch just for the light, see:


Note that the same physics apply regardless of the size of the fan. So it doesn’t matter whether it’s a ceiling fan, a small tabletop fan, or an in wall fan: don’t use a light dimmer.

If you just want on/off control, then look for an “appliance module” rather than a “lamp module.” (Of course always check the specs for the specific model fan to make sure the module can handle it.)

If you want control of the speed, then you either need to use one of the fan control switches like the Leviton or the GE, or for a small fan you can get a “motor control” device.


I purchased the GE Smart Fan Control, the box and device itself indicate that it’s a fan control, but when I try to add it in the SmartThings interface, it shows up as a GE Smart Dimmer … do I have a defective device? Or is there some sort of interface issue I’m running into on the app? I’ve been searching far and wide for someone who’s done this particular install, and haven’t found anything relevant yet. Thanks!

You need to install a custom DTH for it or it just shows as dimmer. It will still work. 0-32% is Low 32-66% is Medium and 67-100 is High or something like that. With the DTH below, you just have 3 levels only.


Great info. Thanks for posting.

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Just wanted to mention that there is a 2017 FAQ on devices to control a fan which has information on the most current options, including some that were not available when this thread was first posted.