100,000 BTU/hr furnace will use about 97 cubic feet of natural gas (100,000 ÷ 1,030 = 97.1) in one hour
100,000 BTU/hr furnace will use about 40 cubic feet of propane (100,000 ÷ 2516 = 39.7) in one hour
What exactly is Propane?
As defined by the Propane Education and Research Council, "propane is a hydrocarbon (C3H8) and is sometimes referred to as liquefied petroleum gas, LP-gas, or LPG. Propane is produced from both natural gas processing and crude oil refining, in roughly equal amounts from each source. Nearly 97 percent of propane consumed in the United States is produced in North America. It is nontoxic, colorless, and virtually odorless. As with natural gas, an identifying odor is added so the gas can be readily detected."
The Council also affirms there is no danger in the use of propane. "Propane is an approved, clean fuel listed in the 1990 Clean Air Act and the Energy Policy Act of 1992 and is one of the cleanest burning of all fossil fuels. Tests conducted by the U.S. Environmental Protection Agency show that propane-fueled vehicles produce 30 percent to 90 percent less carbon monoxide and about 50 percent fewer toxins and other smog-producing emissions than gasoline engines. Propane also is nontoxic, so it’s not harmful to soil or water."
Propane is labeled a 'green' fuel as it as relatively no emissions or toxins when burned and released into the atmosphere.