Q: I just replaced my natural gas furnace so I don’t want to do heat pumps. Does it still make sense to do the other 3. If so, in which order?
A: Yes it does. Insulation (and draft sealing), and triple-glazed windows (either replacing the whole window if the window is rotten or adding window inserts if the window is in good shape) will cut your energy bills not matter what the source of heat is. I suggest doing insulation and draft sealing first because they have the highest return on investment and often pay for themselves in a few months. Windows take longer to pay for themselves. The incremental cost of triple-glazed windows over the cost of double-glazed windows will pay for itself on our house in about 6 years. The cost of window inserts pays for itself in about 5 years – see chapter 3 in Zero Carbon Home for details. After that, I would do enough solar to offset your entire electric bill. If you are thinking of getting an electric vehicle or two then add on about 3,000kWh a year for each car. In most places this would be about an additional 3kW of solar panels or about 8 additional panels. This will get you about 12,000 miles per car at around 2c per mile. A gasoline car doing 30 mpg costs about 10c per mile. An average roof in MA can generate 3,000kWh per year from a 3kW array which will cost you about $8,000 before subsidies and about $3,000 after the federal and MA subsidies.