Right, that’s a bad financial investment. If I put $100 in the stock market, in 10 to 15 years, I will have $200 to $300, on average. If I put $100 into solar panels, in 10 or 15 years, I will have break even.

In the US, most people don't live in one house that long.

That should be a wash with the value that a house gets sold for.

Yes and no. A house's value is largely based on the price of other comparable houses in the area that have recently sold. It's very possible to "overimprove" a house and you will not recoup those costs when you sell. Whether the furnace is brand new or 10 years old will have a negligible impact on the selling price.