This is probably SO obvious I'm not seeing it, like all the times I'm looking for my sunglasses and they're on my head.

I know how to figure return on investment and IRR if I have a starting amount, and it grows or shrinks. but what about when I make an investment in a heating system. I assume the investment immediately goes to zero (I am conservative and don't want to count on any return on investment from the increased value added to the building). How do I figure my investment return if I invest 10K, it goes to "zero" by virtue of that being the cost of the new heating system but it saves me $3,000 per year?

Thank you!