Compare the running cost of gas heating versus electric heating.
Comparing heating fuels only works if you compare delivered heat rather than purchased energy, because the two systems convert differently. A gas furnace at 92% AFUE burns about 1.087 therms for every therm of heat in the house. A heat pump moves heat rather than making it, so at a seasonal COP of 3 it buys one kilowatt-hour for every three it delivers — which is why electricity at four times the price per unit energy can still win. Convert the annual heat demand to therms on the gas side and to kilowatt-hours at 293.07 kWh per MMBtu on the electric side, divide each by its conversion efficiency, and multiply by the local price. Set the COP to 1.0 and you get the resistance-heating comparison instead, which gas nearly always wins.
Gas vs Electric Heating Cost
Gas cost = heat MMBtu x 10 / AFUE x price per therm; electric cost = heat MMBtu x 293.07 / COP x price per kWh
Roughly when the electricity price per kWh divided by the COP falls below the gas price per therm divided by 29.3 times the AFUE. At $0.17/kWh and $1.35/therm with a 92% furnace, the crossover is near a COP of 3.4.
Rated COP is measured at mild conditions. Seasonal performance falls as outdoor temperature drops, and any resistance backup heat that engages on the coldest days runs at a COP of 1.0, dragging the average down.