We finally received our first winter electric bill yesterday. Between living in central Texas, where summer hangs on into October, and our well-insulated house, we didn't even turn the heat on until about Thanksgiving, so this bill covering December 8-January 10 was our first full month of winter. The total bill, including water, wastewater, garbage service, etc., totaled $128.74, of which about $60 was actual electrical usage.
I'm going to try to compare our utilities here versus a winter month in the condo, like I did with our first summer bill after we moved in, but winter is a little more complicated because our furnace and water heater in the condo were powered by gas, whereas now our geothermal heat and water heating (also assisted by the geothermal system) appear on our electric bill. And since our water was sub-metered by the condo association, I need to add our December 2008 gas ($63.26), electric ($70.14), and water ($25.16) bills, which comes to $158.56. Now, for a fair comparison, I have to add our current gas bill to our current total, but since our only gas appliance is the range, that's only about $12, for a total of about $140 for utilities last month. Adjusting for the $15 of garbage service that we currently pay to the city, versus garbage service that the condo association paid (but we ultimately paid, of course, through our monthly fees), we're looking at about $174 in the 1,200 square foot condo versus $140 in our nearly 2,300 square foot house.
Looking at it in terms of electric usage, we used 787 kilowatt hours (kwh) of electricity last month, whereas we used 621 kwh for a comparable time period in the condo. However, the true comparison is 787 kwh of electricity in the house versus 621 kwh of electricity plus 5,000 cubic feet of gas in the condo...and if there's some way to convert gas to electricity for comparison purposes, I don't know it, so we'll just have to settle for an apples-to-oranges comparison on this.
Looking at it one last way (but sparing you the math this time), if we extrapolate our energy usage (not including fixed customer charges, etc.) from the condo to a house that's twice as big and built with comparable (traditional, not "green") systems, insulation, etc., we could expect that our utilities would have come to about $270 last month. Thus, my best estimate is that building green (which is certainly not cheap) saved us about $130 in energy last month -- which, at our unbelievably low interest rate, covers principal and interest on about $26,000 of our mortgage.