Rotten Egg Smell Near an Outdoor Vent for a New Furnace

Furnace Fuel

• While some furnaces run on electricity, oil or coal, many use natural gas as a fuel source. In most instances, gas furnaces deliver the fuel to the combustion chambers through an enclosed system that eliminates the possibility of leaks. A strong odor of rotten eggs may indicate a gas leak in the fuel line.

Odor

• In its original state, natural gas does not have an odor. Gas companies and utilities add mercaptan, a chemical that gives the gas a strong, unpleasant odor. The purpose for adding this scent is to alert people to the possibility of a gas leak. One of the most likely places for you to notice this odor is near your furnace when the pilot light goes out. The smell is usually faint and relighting the pilot eliminates the odor.

Causes

• If you notice the smell when your furnace isn’t running, the point of origin is most likely in the fuel line or within the furnace, rather than the exhaust vent. The fuel line that enters your home from the main gas pipe may run near the vicinity of your exhaust vent, creating this odor in the air. If your furnace is on when you notice the smell, the cause may be an inefficient furnace system that fails to burn all the fuel within the combustion chamber. If this occurs, you may smell a slight odor of gas in the exhaust emissions that flow from the vent. Inefficient burning of the fuel can result in higher utility bills and may pose a risk to your safety, due to the flammability of the gas in your exhaust line.

Precautions

• Contact your gas company to inspect the source of the odor, especially if the smell is strong and pervasive. Gas that enters the outside air usually dissipates rapidly. A recurrent or continual smell of gas around your vent line requires investigation and correction by a licensed professional.