I know enough to be dangerous, in that it makes me think there should be a way to do this. I was reading a paper This Thermal House. And one thing kind of stuck in my mind when I read about the circuit equivalent. In electronics, we sometimes simplify a circuit to do things like calculate the battery equivalent, etc. Can the same be done with a house and calculating the R-value. If I know the temperature change over time inside and outside the house, could I calculate an average R-value estimate? Part of my thought process here is that I could put the super fancy R-2000 window in. But if I leave the window open all the time, I'm sure I've kind of blown the R-value.