Furnace Overview

Educate yourself. Understanding is the best way to make sound decisions.

Heat Exchanger

The smaller metal “box” inside the furnace cabinet is the heat exchanger.  (See the figure above.)  (Additional heat exchanger images on Google.)  The heat exchanger is where the gas burners are located.  The heat exchanger is designed to be heated by the burner flames while the furnace blower moves room air across the outside of it.  Under normal conditions, when the furnace is running, the air coming into blower from the house (return air) is generally 60 to 68 degrees F.  As the air passes through the furnace, the heat exchanger warms the air.  The discharge air coming out of the furnace and moving through the duct work will be somewhere between 40 and 90 degrees hotter than the return air.

The heat exchanger is what separates air flow of the fuel burning process from the blower-driven air that moves through your house.  This is a box-in-a-box arrangement.  When the furnace blower is running, it pushes air through inside of the outer cabinet across the outside of the heat exchanger.  The force of the blower-driven air is much greater than the air pressures inside the heat exchanger.  As a result, any crack or hole or split results in air being pushed INTO the heat exchanger.  There is no way air will move from inside the heat exchanger to the indoor air stream.

Natural Gas

Natural gas is a flammable gas, consisting largely of methane and other hydrocarbons, occurring naturally underground.

 Natural gas burns more cleanly than other fuels, such as oil and coal. Burning natural gas produces both water and carbon dioxide, it produces less carbon dioxide per unit of energy released than coal, which produces mostly carbon dioxide. When someone tells you that a cracked heat exchanger will give you carbon monoxide poisoning, ask them how since burning natural gas doesn’t produce carbon monoxide under normal conditions. If incomplete combustion occurs, then carbon monoxide is generated. Incomplete combustion typically comes from to little air available for combustion. Modern high efficiency furnaces receive combustion air from outside the home allowing more than adequate combustion air. If the intake is blocked or other abnormal condition a problem may occur with inadequate air available.

Feature 3

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