|Heating Degree Days||0.21||0.0||47.86|
If I'm reading this correctly, we're saving about 10 therms per month?
I'm a little suspicious of OLS however since both Therms and HDD exhibit strong seasonality. The econometrics literature doesn't seem to address regressing two seasonal series against each other. Most of the univariate time series literature is concerned with autoregressive processes, integrated series, etc.