Good question. I'm really benchmarking the system against itself, year on year, by comparing the weather outside vs. performance (output temperature of the HVA

Good question. I'm really benchmarking the system against itself, year on year, by comparing the weather outside vs. performance (output temperature of the HVAC unit, average temperature inside the house). I'm not trying to find an objective efficiency rating so much as monitor performance over time to see if it's changing.