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.
http://www.fancollectors.org/info/speed.htm
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.