Final answer:
A conventional hot water heater using natural gas has an efficiency of about 85%, while an electric hot water heater can achieve 100% efficiency. However, if the electricity used comes from a natural gas power plant, more total fossil fuel energy may be used.
Step-by-step explanation:
A conventional hot water heater using natural gas has an efficiency of about 85% in transferring heat into the water, while an electric hot water heater can achieve 100% efficiency by using a heating coil immersed in the water. However, if the electricity used by the electric hot water heater comes from a natural gas power plant that has an efficiency of 40% in converting thermal energy into electricity and 95% efficiency in transmitting it to the house, then the total fossil fuel energy used by the electric hot water heater will be more. By calculating the ratio, it is found that it will take 2.2 times more gas at the power plant compared to the home to produce the same result in heated water.