Subtract one temperature from another and put the result in a tile

📐 Rule Machine®
1

I have a Sonoff temperature/humidity sensor in the return air duct to the AC and a second Sonoff temperature/humidity sensor in the ceiling duct from the AC.

Is there a way to subtract the value of the ceiling duct from the return duct when either changes and display the temperature difference in a tile?

Thanks for any suggestions.

2

One way would be to use your favorite rule engine to get the two values and do the subtraction, and then update a virtual sensor for the tile...

3

Using Rule Machine, create three variables. Assign your sensor values to the first two (these can be local variables) and then set variable 3 (probably a global variable) to the difference using the "variable math" operation to subtract the two. Display variable 3 on the dashboard.

You should expect supply air humidity to be 100%. And the higher the humidity in the return air, the lower your temperature difference will be (higher supply air temp).