A gas furnace combusts natural gas, and this generates the heat that warms the air. However, the hot combustion gases cannot come into direct contact with the air that moves through the furnace and into the home because the gases are harmful to breathe. The way a furnace trasnfers the heat from the combustion gases to the air is through a component called the heat exchanger, a chamber that collects the gases so that its metal walls heat up and warm the air moving around the exchanger.
Once the heating process is complete, the leftover combustion gas byproducts safely exits the furnace through a vent. This ventilation stage is critical for the furnace’s safe operation. Problems with the venting can lead to the toxic gas byproducts (principally carbon monoxide) to go the wrong direction and end up in the house and also speed up the effects of corrosion on the furnace.