Typically, gas furnaces cost about 10 to 25 percent more than oil furnaces initially, but the average cost of heating oil is higher than natural gas. Gas furnaces are also about 10 percent more efficient than oil furnaces.
In the winter of 2014 to 2015, the projected average cost of natural gas for U.S. consumers is around $630, while the average cost of heating oil for U.S. consumers is around $1,800. Natural gas is mainly produced in the United States and Canada, which makes the gas supply more constant. In contrast, oil supply depends on global supply and demand, which causes the price to vary more often.