An open wood-burning fireplace emits between 50 and 100 grams of particulate waste per hour, along with large quantities of water, carbon dioxide (CO2), and trace amounts of various other gases. The gaseous emissions from a wood fire are considered by some scientists to be environmentally benign, as a fallen tree will emit the same amount of CO2 gases whether it is burned or left to rot, and the same tree will have converted many times that amount of CO2 to oxygen during its lifetime.
The main environmental concern regarding wood burning is the inhalation of the exhaust particulates, especially those known as PM-10’s, which are particles small enough to lodge in the lungs. Today’s approved woodstoves were created to address this issue; they are required by law to produce less than 4.5 grams of particulate emissions per hour.
The combustion of natural gas doesn’t produce significant particulates; it is the gaseous elements in gas exhaust that are of environmental concern. Gas exhaust is composed mostly of water, CO2, and nitrogen dioxide.
The CO2 from natural gas doesn’t enter the atmosphere unless the gas is burned, so the combustion of gas fuel is considered by some scientists to be a much more significant (and avoidable) contributor to the so-called “greenhouse effect” than the combustion of wood. Further, nitrogen dioxide emissions from natural gas exhaust combine with water in the atmosphere to form nitric acid, which is a factor in the environmental hazard known as acid rain.
Environmentalists seem to have formed two camps regarding the relative environmental impact of the two fuels. The anti-particulate emissions extremists would ban wood fires altogether, while those who view the greenhouse effect and acid rain as the larger environmental threat would strongly disagree, and would also point out that wood fuel is a renewable resource, while natural gas is in limited supply.
Both camps would agree that neither fuel should be burned frivolously: wood fires and decorative gas logs in open fireplaces waste the fuel resource and contribute needlessly to airborne pollution. If you are deciding how best to use your fireplace, install an approved wood insert or high-efficiency gas insert.