One of the most common calls that heating and air conditioning contractors get during the fall and winter seasons, comes after San Diego Gas and Electric (SDG&E) performs a furnace inspection for a homeowner and tells the customer that they have a cracked heat exchanger. A cracked heat exchanger is a serious issue – so much so that SDG&E usually puts a red tag on the furnace and may shut off the gas, lock the utility meter or actually completely disconnect the furnace. A red tag on the equipment states that the furnace has been shut down and is dangerous to operate unless repaired or replaced.

A dysfunctional furnace can emit carbon monoxide, which is a colorless, odorless and tasteless gas formed when carbon-based fuels are burned with inadequate amounts of oxygen. This condition is known as incomplete combustion.
“A cracked heat exchanger in a furnace can emit carbon monoxide and put homeowners at serious risk,” said Gabriel Carini, president and owner of Carini Heating, Air and Plumbing, a heating and air conditioning contractor in San Diego, CA. “Carbon monoxide poisoning is deadly, which is one of the reasons all California homeowners are now required to install carbon monoxide detectors in their home.”

What Causes Heat Exchangers to Crack?
Cracks in metal surfaces can be caused by the natural process of stress and flexing as the metal contracts and expands during heat up and cool down cycles, especially near weak areas such as bends or welds. Eventually, this process results in cracks or failure of the heat exchanger. Over the years, every furnace will experience this type of failure. Different factors cause the failure but a lot is determined by how the unit is maintained, and the quality of your installation. The most common cause of an overheated heat exchanger can be as simple as a dirty air filter. A clogged air filter restricts airflow through the furnace, overheating the heat exchanger, and eventually resulting in stress cracks.

Another cause of furnace overheating and subsequent cracking is a furnace that is too large for a house and undersized ducting. Under-sized ductwork can cause a lack of proper airflow and result in the same kinds of problems as a clogged filter.

Unfortunately, cracked heat exchangers cannot be repaired, but consumers should beware of scams by unscrupulous contractors that immediately try to sell a furnace replacement without proving the heat exchanger is truly cracked. The heat exchanger is at the center of the furnace, so to replace this component, nearly the whole furnace must be disassembled, which can be costly. And even if the furnace parts are protected under warranty, labor and freight will start around $500. Without a warranty, a heat exchanger replacement could run as much as $2,000, which is around the cost of a new entry-level furnace.

“A cracked heat exchanger is pretty easy to spot using small video cameras that fit into areas that cannot be seen by the naked eye,” said Carini. “This allows for more thorough inspections because the heat exchanger can be viewed from different angles.”

For more information, contact: Carini Heating, Air and Plumbing, 619-843-0997,