return on investment if initial investment not counted

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!