The average energy cost to run a furnace depends on the type of fuel it uses, the efficiency of the furnace, and local energy prices. Natural gas is often considered one of the more cost-effective options, totaling an annual cost between $400 to $700, while electricity tends to be pricier at $1,600 to $2,200 annually. Furnace efficiency is crucial in determining energy costs, as more efficient models require less energy to produce the same amount of heat. Regular maintenance, proper insulation, and thermostat management also play key roles in overall energy consumption.