As of December 7th, the eGuage energy monitor has been installed for a full year, giving me the ability to know how much energy it took to heat our house for a full one-year period. The data was actually a bit better than I anticipated:
Total kWh used to heat the house for the period December 7, 2014 through December 6, 2015: 2,549.6534
At 15 cents per kWh (winter rate) that resulted in a total cost of $382.45 (This includes all charges on our electric bill).
Knowing that natural gas is generally much less expensive than electricity, I thought it might be interesting to compare the two. In other words, if we heated the house with natural gas, what would the cost have been? Here are my calculations. Feel free to let me know if you think my numbers are incorrect:
One kWh of electricity will generate approximately 3.14 kBtus of heat energy. Therefore, our house used 8,007 kBtus of energy to heat the house during the one-year period.
8,007 kBtus equals 8,007,000 btus.
A “therm” of natural gas produces approximately 100,000 btus and costs approximately 79 cents (of course, this varies by location).
Therefore, if our house had a 100% efficient natural gas furnace, it would have used slightly more than 80 therms of natural gas for heat (8,007,000/100,000) and that would have resulted in a cost of $63.25 for the year.
Now, of course, we can’t use natural gas for several reasons; natural gas is not available where we live, they don’t make a natural gas furnace small enough, and a Passive House is so tight that burning any fuel in it is not advisable. But I thought the comparison would help put the energy efficiency of a Passive House in perspective for those who use something other than electricity to heat their home.
Some other highlights from the one-year data:
The water heater used 715.516 kWh; about 31 cents per day.
The clothes dryer used 634.7463 kWh; about 28 cents per day on average.
The ERV used 369.02674 kBtus; about 17 cents per day. However, it should be noted that the ERV was off for an estimated 50% of the three summer months because we had the windows open.