Your landlord wants to replace the old, inefficient gas furnace in your apartment, but they want to understand the potential cost savings before making a decision! The existing furnace (Option A) has an average efficiency of 70%. They are considering two replacement options: (Option B) a 90% efficient gas furnace and (Option C) an air to air heat pump with an average coefficient of performance (COP) of 2.85. For the sake of simplicity, assume that the efficiencies and COPS above are consistent annual averages that account for total HVAC system efficiency. After analyzing the utility bills, you conclude that the existing furnace consumes 21,500 kBtu of natural gas over the course of a typical winter, and you note that the cost of electricity is $0.11/kWh while the cost of natural gas is $110/therm. Calculate the annual operating cost of each option (A, B, C listed above). Which option has the lowest annual operating cost? How much money do you save each year by switching to that option?