Newer, more efficient furnaces are often considered to be better for the environment than less efficient models. However, determining how much of an impact a furnace has on the environment requires weighing a number of factors.
Most furnaces are powered by natural gas, and others are powered by heating oil. Furnaces powered by fossil fuels have become far more efficient over the years, although they still release carbon dioxide into the atmosphere. Furnaces have to reach a certain efficiency level to meet government certification requirements, and some of these upgrades drive up their prices.
Electric furnaces can be friendlier for the environment, depending on how they are powered. Solar and wind power plants do not emit carbon dioxide, although they are rare in the United States as of 2015. Nuclear power also releases only trace amounts of carbon dioxide.
Wood-burning furnaces are somewhat controversial. Wood releases carbon dioxide when it burns, but trees planted to replace the ones cut down absorb a roughly equal amount of carbon dioxide over time. Because of this, some consider wood-burning furnaces to be carbon neutral. Burning wood, however, also releases a significant amount of particulate matter into the air, which can cause and aggravate respiratory problems and cause some environmental harm. Those in remote locations, however, may find them to be a superior option compared to furnaces that burn fossil fuels.