Reply to Blick,
What are you plotting on the second graph with the element, "HVAC ? Temp 2˚ F"?
That is a remote temperature transmitter with the probe stuck into the forced air vent nearest to the central heating unit, an all season heat pump. HVAC stands for heating, ventilating and air conditioning. I use the HVAC for heating as well as a propane heater with sufficient capacity to heat the whole house by itself. It used to be a wood stove, but I got tired of that after 3 seasons being here. Heat pumps are not very efficient when the temperature gets down into the 20's F. Plus, the propane unit is good insurance for if and when the power is lost.
Graphing the HVAC unit gives me a good idea of how much it is running. With both units on their respective thermostats set to the same temperature, the lag in keeping the room temperature on set point with the HVAC unit at lower temperatures is picked up by the propane unit. When it get warmer outside the HVAC keeps up better and therefore takes more of the burden of heating the house.
At first, I tried running the house on just propane, but it warmed one end of the house a little too much and the other not quite enough. And, I ran out of propane after 6 weeks of mostly mild Winter weather. By the time it turned really cold, I was using the shared load system and still ran out of propane after 6 weeks.