I need help with setting a plug to turn on when my hvac is running.
I had to install an inline fan in my hvac system to get more heat into an addition on the house. I dont want this fan to run all the time when the hvac is not running.
If your thermostat exposes State it is easy. But some thermostats don’t expose State like my Honeywell T5 and Google Next don’t expose State. The following is an example when State is exposed.
If state isn’t exposed you would need to base your automations on temperature
And this is the point we ask, what is the make and model of your thermostat? What make and model of outlet is your fan plugged into?
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Makes sense and a miss on my part for not including the model info. I am running a Honeywell t5+ and the plug is legrand radiant wifi matter.
I do not have state displayed. So sounds like i need to do so thru temperature automations.
This in my first attempt.
On my furnace there is an output for a humidifier. When the furnace is on, the humidifier output is 24VAC. I use it as an input to a relay, along with a humidity sensor, to determine if my furnace-mounted humidifier turns on.
So, you could use this as a trigger for your fan. The humidifier output would be a trigger for a relay that turns on your fan. I use a Shelly z-wave relay (driver=z-wave switch) to drive mine. Since it is a smart relay, you could also use the relay state to drive a smart plug instead of directly wiring them together.
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Appreciate the response.
I dont love my thermostat.
Anyone have recommendations on one that displays heating status on smartthings?
I’d swap out the thermostat to make life easier. Always have issues with the thermostat not responding to smartthings
Another way to solve this problem is an airflow switch, such as this one. Perhaps you wish to do other actions in conjunction with the logic “HVAC is ON” and if that’s the case there are other duct-mounted airflow switches that may fit the bill when paired with some Z-Wave (or Zigbee or whatever) input device to the SmartThings system.
Lots of options, but choice is good! 
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