I am the second owner of a 3500 sq. ft. home with a ClimateMaster Tranquility 27 geothermal system and electric auxiliary heat. This is my fourth winter in the seven year old house, and I've noticed that my electric consumption during the heating season seems to be trending upward from year to year. I realize that my first winter in the house was unusually warm and that last winter was unusually cold, so I decided to try and compare with electric consumption with heating degree data. My electric utility has a website where I can download daily consumption in an Excel spreadsheet and I can also download weather information (minimum temperature, maximum temperature, heating degree days, etc.) from the government website in another Excel spreadsheet. I was expecting to see a rather strong correlation between HDD and electric consumption in the "mild" weather (when the auxiliary heat was not running) and a different correlation in the very cold weather (when the auxiliary heat was running a material percentage of the time.) I was also expecting to be able to see the approximate temperature (either in HDD or minimum temperature) when the auxiliary heat was running for a material percentage of the time. When I made my analysis I didn't find quite the correlation that I expected, and I found some recent data that didn't even look reasonable (especially when compared to prior year data.) I've listed four consecutive day's data from the last two years for comparison. Date Minimum Maximum HDD kWh 1/6/14 -15 5 70 220 1/7/14 -14 8 68 185 1/8/14 6 25 49 113 1/9/14 11 31 44 78 1/6/15 9 19 51 67 1/7/15 -6 12 62 147 1/8/15 -7 20 58 363 1/9/15 1 21 54 198 We keep the thermostat in the mid 60's, the compressor seems to run nearly all the time when the outside temperature is below the low 20's, and the inside temperature rarely drops below the set point. The auxiliary heat (20 kw) obviously runs in the "cold" weather, but I don't have a way to track the run time. Has anyone else tried to compare their electric consumption with degree days? If so, what did they find? What does my 2015 pattern suggest? (My first thought was bad data from the utility----but they deny that as a possibility.) The reported usage on 1/8/15 suggest that my auxiliary heat ran for at least 15 hours. I find this hard to believe, but is it possible that the heat pump contributed almost zero heat even though it ran (almost?) all the time? Any other thoughts?