A: See Chapter 2 in the book. I recommend keeping the furnace and replacing your AC units with heat pumps. Heat pumps cost less to run if you power them with solar panels. See below for the likely difference to your heating bill and carbon footprint from adding heat pumps:
Adding a heat pump will have dramatic effect on a home’s heating bill and carbon footprint, but the effect varies considerably depending on what heating fuel is currently being used and what the source of electricity is for the home.
Effect of adding a heat pump:
| If currently heating with natural gas | If currently heating with heating oil | |
| If using Eversource or National Grid electricity (at 23c/kWh and 0.87lbs CO2/kWh) | 150% increase in heating bill 10% cut in carbon footprint | 25% increase in heating bill 45% cut in carbon footprint |
| If using Municipal Light and Power electricity (at 14c/kWh and 0.87lbs CO2/kWh) | 50% increase in heating bill 10% cut in carbon footprint | 25% cut in heating bill 45% cut in carbon footprint |
| If using Rooftop solar panel electricity (at 8c/kWh and 0lbs CO2/kWh) | 10% cut in heating bill 100% cut in carbon footprint | 50% cut in heating bill 100% cut in carbon footprint |
This assumes that the heat pump achieves a year-round COP (coefficient of performance, or efficiency) of 2.3, which is the average found in a review of the work of several researchers on Mitsubishi, Daikin and Bosch heat pumps in New England. Both ducted and ductless systems were included. In general, ducted systems had higher COPs than ductless systems and Mitsubishi had the lowest COPs, as low as 1.3 in one case. The manufacturers claim COPs of between 3 and 5 for these units. None of them perform to the manufacturers’ specifications under real-world year-round conditions in New England.