The heat exchanger in your heating system heats the air in your furnace and water in your boiler. It’s one of the key components that provides heat throughout your home during cold winter temperatures.

When ignited, either by gas, propane or oil, the system channels hot combustion gases into the heat exchanger chamber to heat the metal walls. If your system is a warm air furnace, the return air ducts suck the cold air in your home into the furnace, which then passes over the heat exchanger to warm the air that gets distributed throughout your home. If you have a boiler, the return water passes through a coil that is heated by the heat exchanger to deliver hot water through your baseboard, thereby warming your home.

The heat exchanger system begins at the systems burner assembly and ends where it connects to the chimney vent. The heat exchanger is where flue gases from the burner assembly pass through to vent harmful gases to the outside of your home.

If you suspect your gas furnace has a cracked heat exchanger, you shouldn’t ignore the instinct. A damaged heat exchanger can be potentially hazardous to your family if not repaired immediately, as it exposes toxic gases like carbon monoxide.

There are telltale signs you have a problem with your heat exchanger. If the burner flame looks yellow, the burner can be dirty or damaged, or your heat exchanger can be cracked. Typically, the flame should be blue, providing insight that your system is functioning efficiently.

If you notice a lot of soot around your heating system or at the air vents of your ducted heating system, it may be a sign there is carbon spewing from your heating system. Soot is an indication that gases are not burning completely – this is known as incomplete combustion. Faulty or cracked burners, a cracked heat exchanger, or an issue with the flue vent, are a few reasons this can happen.

The most notable sign of a compromised or cracked heat exchanger is a strong smell. The fumes usually smell like formaldehyde and are highly toxic to your body when inhaled.

If you discover that your heating system produces a formaldehyde-like odor, or if you are experiencing some unexplained health issues, you should immediately contact a professional heating contractor. Ignoring the issue will only expose you and your family to more harm and danger.

If there is water collecting around your heating system, it may also be a sign that there is a problem with the heat exchanger. However, that is not always the case. If you have a whole-house humidifier connected to your furnace, it may need to be serviced. Or if you have a hot water or steam boiler, the pressure in your boiler may be too high, causing your relief valve to leak. In any of these situations, it is time to call a heating professional.

There are a few reasons why a heat exchanger can crack, but the most common is overheating. If the airflow in your warm air furnace is too slow or if an air filer is blocked, heat will build up in the heat exchanger and cause it to overheat and crack. That’s why maintenance is so important. A technician will check to ensure proper airflow is provided.

A heat exchanger can also crack due to constant heating and cooling. As the exchanger heats and cools intermittently, the chamber’s metallic wall expands and contracts. As a result, the metal component will wear down and crack. This happens more frequently when a heating system is oversized.

Another reason your heat exchanger could crack is corrosion or rusting. Rust tends to eat away any metal and could cause a crack on the heat exchanger. A leak in a water boiler that goes unaddressed, or a defective chimney vent that gathers condensation can be the culprit. When routine service is not provided, these types of repairs go unnoticed and rust can build on components, thereby causing damage.


The average lifespan of a heating system’s heat exchanger is about 15 to 20 years. Operating a heating system with a cracked heat exchanger can be very dangerous. It will not only pose significant risks to your health but also cause it to operate less efficiently and increase the likelihood of damaging other components in the heating system.

If carbon monoxide gas seeps into your home, it can result in headaches, nausea, vomiting, and dizziness. Prolonged exposure to high levels of carbon monoxide can cause heart diseases.

If you believe that your furnace has a cracked heat exchanger – shut it down and call a qualified, licensed and insured heating professional. They will determine if you’ll need to replace your cracked heat exchanger or replace the entire system.

Cracked heat exchangers and carbon monoxide poisoning are responsible for hundreds of fatalities a year. To keep your family safe, you should invest in an annual inspection and maintain your heating system regularly.

Tom Scarangello, General Manager       Scaran Heating & Air Conditioning

(718) 984-0805