A crack is never a good sign under any circumstance. It should never be ignored as it indicates a problem or fault that could potentially be dangerous. When there is a crack, it is only right to act to fix it in time.

Our gas furnaces’ heat exchangers are prone to cracks, and once it is suspected that this component is damaged, we should seek solutions at once. But now, the question is, how do we even know when our heat exchanger is cracked?

Cracked heat exchanger symptoms suggest that our furnaces are in bad shape, though we may not be able to detect them. Hence, it is essential to be aware of these signs to determine when this component is defective. Then, we can proceed to repair it immediately to avoid any hazards.

In this article, we’ll cover everything you need to know about cracked furnace heat exchanger symptoms.

What is a Heat Exchanger?

A heat exchanger is a component in a gas furnace, an HVAC unit that warms your home in cold weather. This exchanger is a system that comprises coils and tubes in a constant loop, and the primary function of this setup is to heat the air that passes through it.

The heat exchanger system extends from the furnace’s burner assembly to the chimney vent. This gas furnace unit is confined within a metal chamber, which helps to distribute warm air in the home.

In the process of providing warm air to your home, the walls of this metal chamber are heated by the hot combustion gases from the furnace. While the walls are continuously stoked, the cold air in your home is sucked into the air ducts and passed along the hot metal chamber. Once the air has warmed up, it will be redirected back into the rooms of your home.

Signs of a Cracked Heat Exchanger

A mere look may not be enough to tell that your furnace’s heat exchanger is broken. However, there are a few cracked heat exchanger symptoms that suggest there are faults with your heating system, and they include:

Yellow Furnace Flame

Ideally, the flame of a gas furnace is blue. A blue flame indicates that your furnace is in good condition and the heat exchanger is functioning correctly. But when the furnace flame is yellow, there is likely a problem with your heat exchanger. This color change could also hint at an unclean burner.

A fully-functional furnace burns with a stable blue flame. So, if you notice an unsteady blue flame, the chances are that there is an issue with the unit.

Soot Production

Sometimes, the formation of a yellow furnace flame results from the incomplete combustion of gas. This produces a lot of soot and carbon deposits within the furnace. While there are many reasons why gas may not burn completely in your furnace, including the broken burners, a cracked heat exchanger is usually the culprit.

Emission of a Foul Smell

A cracked heat exchanger is known to pollute the air with an offensive odor. Notably, this foul smell can be likened to that of formaldehyde – a colorless gas compound used to produce various household materials. This formaldehyde-like stench is dangerous to your health and could irritate your skin and eyes.

Corrosion and Rust

When you notice that your furnace’s external components are starting to rust or wear off, there is a strong possibility that the internal parts are in a similar condition. Ultimately, this means that your heat exchanger may have begun to suffer wear and tear.

Quite frankly, this deterioration is a common problem in household furnaces. It is connected to the expansion and contraction of the unit’s components due to alternate heating and cooling. Also, the continuous exposure of the furnace components to moisture and other mineral elements is the leading cause of rust and corrosion.

Water Leakage

This is one of the major symptoms of a cracked furnace heat exchanger. Water leakage can also be caused by other things, such as a leaking whole-house humidifier or a clogged HVAC drain system. In any case, a professional HVAC technician should be able to help decipher the actual cause.

Causes of Cracks in Heat Exchangers

Your furnace could be working perfectly one minute, only for it to show symptoms of a cracked gas furnace heat exchanger the next. Here are some possible reasons your heat exchanger would crack.


Overheating is one of the main reasons why oil furnaces develop cracked heat exchanger symptoms. It is caused by heat accumulation in the system, resulting from slow airflow within the furnace.

Alternate Heating and Cooling

Furnaces heat up when they are in use and become cool during their period of inactivity. It is worth noting these temperature changes can affect your heat exchanger, causing it to develop cracks from continuous expansion and contraction.


As the walls of your heat exchanger continuously wear off, it could eventually get cracked.

Age of the Furnace

Towards the end of its 15-year lifespan, the heat exchanger in a furnace is prone to cracking. So, it would be best to find a replacement as the current one nears its final days.

You can forestall heat exchanger problems by periodically maintaining your HVAC system. If your furnace is already showing any of the cracked heat exchanger symptoms listed above, it is not advisable to fix it yourself. There is a need to contact a professional HVAC technician to have a look at your furnace.

Anderson Air offers free in-home consultation, and you can contact them by visiting Their team of skilled professionals is always ready to help you put your heat exchanger system in perfect order.