What is a solar supplement? Here on the west coast of Michigan, we're having our 11th day in a row with 0% of potential sunshine...

I did a heat loss calculation on our house, and then calculated the heating season BTUs from NOAA data on degree-days for our area.

When I then compared this total to the gas bills over the last 4 years, the calculations corresponded exceptionally well.

Unfortunately, the calculations verified that I have very little attic insulation and leaky, junky windows!