It doesn't seem like the chart of costs includes the effect of summer A/C.

And the chart that is shown peaks in winter a couple months early.

Overall, it seems to significantly underestimate my energy costs.

The conclusion is also confusing: it says I would save $89/year or $24K in 15 years. Huh?

$89/year doesn't seem like enough to justify any investment, and $24K is about $1600/year or ~95% of my current costs, which seems too high to believe.