Gas furnaces have become one of the most common types of home heating systems over the last few decades and have become more efficient and effective over time. With regular maintenance, gas furnaces can last for many years and provide consistent and reliable heat within the home. However, like all home appliances, they can have problems and failures which can become dangerous to the home’s occupants and lead to expensive repairs.
While there are many important parts of a furnace that all work in tandem to make the appliance function properly, the largest component inside of a gas furnace is the heat exchanger. Heat exchangers, which are typically metal tubes or shells, operate by transferring heat from one area to another. Natural gas or propane is ignited and the hot exhaust gas passes from the burners through the heat exchanger. As the metal of the heat exchanger heats up, air from the circulating central air system passes over the metal, heating up and moving the warm air throughout the home.
As a heat exchanger gets older, the chances of the exchanger becoming worn and cracked increases. Cracked heat exchangers are dangerous since the heat exchanger is what separates the hazardous combustion gases from escaping the furnace housing and circulating into the interior of the home. Carbon monoxide is a byproduct of combustion and can be extremely dangerous indoors. Since it is both invisible and odorless, carbon monoxide can be a silent killer.
Heat exchangers are put under a significant amount of strain over time and can become deteriorated or cracked when older. Metal in the heat exchanger cycles between hot and cold, resulting in the metal contracting and expanding repeatedly. This repeated cycle of contraction and expansion stains the metal and can eventaully result in cracks, deterioration, or damage in different areas of the exchanger.
Cracked heat exchangers are difficult to diagnose since the exchange is typically not visible without disassembling the interior furnace components. As such, the identification of a cracked heat exchanger is not part of a home inspection. One sign of a possible cracked heat exchanger, however, is if the color of the burner flames changes rapidly between orange and blue or flickers a solid orange. Natural gas furnaces in good working order will typically have burners that stay a relatively consistent blue color. If your furnace burners change color rapidly or are a solid orange color, having an HVAC contractor evaluate and service your furnace is recommended.