How do I determine when HVAC is 'running'?

I am putting temperature sensors in the registers so I can gauge the delta between the return temp and supply temp. I want to alarm if the delta is not great enough. The problem is that I need the following to happen:

  1. Must determine when the thermostat is calling for heat/cool
  2. Wait 5 minutes and take a reading on the supply temp sensor
  3. Calculate the delta between supply and return temp and notify if the delta is under some amount I determine.

I don’t think I am going to be able to do this without coding, but wanted to see if you had ideas.


What type of thermostat are you using and is it connected to smart home platform?

1 Like

Hi Terri. Thank you for replying. I have spent a lot of time in sharp tools since I made the post and figured out exactly how to do all of this. Thank you!