Energy Audit (WellHome)
As you'd need to maintain those $370/year savings for 54 years to gain any return on your investment you do need to consider other factors.


As you point out - you need to work out if it significantly increase the value of your home. Another side to this though is would it make your house significantly easier to sell? In a buyers market if you can offer things that others can't - full insulation, double glazing etc. then you might find a buyer more quickly and one willing to meet your asking price.
Pure environmental altruism is, by definition, impossible to put a figure on. Only you can decide whether $20,000 is an "investment" you want to make.


Finally, something that has just occurred to me. By doing this work you might get ahead of any future legislation requiring you to fit double glazing, extra draught-proofing etc. So if you can afford it now you won't have to make the investment later when you might not be able to afford it or when prices go up because there's more demand. The downside to this is that future laws might be stricter or have tighter limits which would mean that you still need to do some work.