Older furnaces can develop major issues. One of those issues is referred to as a “cracked heat exchanger.” In Boise, we run our furnace and heating systems the majority of the winter, which equates to shorter life/longevity. Yearly and routine maintenance will certainly prolong the life of your heating system but will also guarantee safe operation all winter long.

So, let’s break this down and hopefully provide some perspective on this common furnace problem.

What Is a Heat Exchanger?

All winter long, the heat exchanger is responsible for holding the flame and removing the harmful byproducts of combustion- carbon monoxide, water vapor, and caustic condensation. These byproducts escape out of the furnace through the venting system and vent outside where it is safe. The heat exchanger dissipates the heat into your home via the airstream when the furnace fan motor kicks on.

Most furnaces have more than one heat exchanger ‘cell’. The more cells, the larger the furnace’s heating capacity is. We like to think of the heat exchanger as the heart of the furnace heating system. It is a vital part of the safe and guaranteed operation all winter long. The heat exchanger is responsible for exchanging heat- how amazingly simple! Ha!

Higher efficiency furnaces have 2 heat exchangers- a primary and a secondary. The secondary heat exchanger in a higher efficiency furnace contains a lot more condensation than the primary and is usually where the crack or fracture will develop. While it can be more difficult to troubleshoot and perform a thorough inspection, we must check this part of the furnace for any cracks in the heat exchanger.

The heat exchanger is like the heart of the furnace. It is one of the most important components to furnace operation.

What Causes a Cracked Heat Exchanger?

Because heat exchangers are holding such an immense amount of heat from the flame and combustion, major amounts of stress wear down the poor spots throughout the chamber. Bends, welds, and rivets are all considered poor spots where excess heat stress can cause quicker and more severe damage. Take note of the picture below:

Nearly all premature heat exchanger cracks are caused by overheating. When a furnace cannot get enough airflow, the heat exchanger overheats and suffers excess stress from expansion and contraction. Over time, the heat stress causes cracks near weak areas such as bends or welds. The most common cause of an overheated heat exchanger is as simple as a dirty air filter. A clogged air filter restricts airflow through the furnace, overheating the heat exchanger, and eventually resulting in what is normally referred to as “stress cracks.”

An oversized furnace can also cause overheating and heat exchanger cracks. “Oftentimes we see furnaces that have too little ductwork,” says James Barrett, a technician for Access Heating & Air Conditioning. Undersized ductwork is the number one cause of a cracked heat exchanger. This is oftentimes overlooked by other companies in the Treasure Valley who simply overlook the underlying issues related to furnace failure.

One of the byproducts of combustion is water. When a furnace first lights, the flame impinges on the cold heat exchanger and water vapor from the flame condenses on the inside of the heat exchanger. After just a few minutes of run time, the heat exchanger is warmed, and the condensation evaporates out through the venting. However, an oversized furnace will heat the home so quickly that the furnace shuts off after only a few minutes, so the heat exchanger stays wet and rusts from the inside out. The frequent cycling of an oversized furnace also increases the expansion and contraction of heat stress on the heat exchanger. A lot of heat exchangers first develop this “flame impingement” before actually developing a crack in the heat exchanger itself. This is the first sign of failure.

Certain brands have lower quality aluminum and steel alloys which do not last as long as stainless steel. It is becoming increasingly difficult to find a brand that has a heat exchanger built for the long haul-20+ years in today’s market. But, with proper installation methods, we can get longer life.

Lack of routine maintenance also shortens the life of the heat exchanger and can cause premature failure from a cracked heat exchanger. Our maintenance packages cover gas pressure adjustments and general/light cleaning of the air movement systems which allow greater airflow across the heat exchanger. Routine maintenance that homeowners can provide is to change their air filters consistently. Dirty air filters cause restriction and less airflow to travel across the heat exchanger.

If a heat exchanger has cracked and your furnace is less than 10 years old, it would be worth the time to diagnose why the heat exchanger cracked. Regardless of whether you replace the furnace or just the part. You don’t want to replace the heat exchanger and not address the root cause/issues…

How To Properly Diagnose A Cracked Heat Exchanger

Because of the amount of surface, a heat exchanger contains and all the nooks and crannies inside the furnace, it can often be difficult to properly diagnose a cracked heat exchanger. We have seen other companies mark the sides of a heat exchanger with a pencil and show that to a homeowner with a fancy high-powered imaging camera. A non-suspecting homeowner can easily fall prey to a company just looking to sell equipment instead of taking care of the customer’s home and the safety of the family.

Thankfully there has been a study, by the AHRI, (AHRI Guideline X-2009) that provides some governance that protects the homeowner and our company. Many companies will diagnose the levels of CO in the home. While this can be helpful for the safety of the occupants it does not provide an accurate diagnosis of a cracked heat exchanger. There are too many variables that can throw a simple CO reading test off, like an inversion in the Treasure Valley, or a leaky and uninsulated home. The AGA (American Gas Association) states that if there is a crack in the heat exchanger (which they define as “a separation of 2 materials”) then the gas supply line needs to be shut off and the furnace system red-tagged to prevent future operation until the issue is resolved. Sound serious? A cracked heat exchanger is not to be taken lightly because of the safety risks it can pose to your home.

Finding a crack or fracture, that is visible, is most important. Even if there is a high level of CO in the home, this doesn’t necessarily point to a cracked heat exchanger. It is the job of our technicians to locate the crack and then explain, with visual confirmation, to the homeowner the problems and solutions for repairs.

We use a variety of testing procedures, from simple mirrors to analyzing the combustion from the heat exchanger. Downflow furnaces compared to up flow models impact the methods of how we test. There are many visible signs, or “red flags” that our licensed technicians can find inside the furnace before even inspecting the heat exchanger. During our inspection, we sometimes find a crack that needs to be verified by a second, third, and sometimes fourth angle. Finding a crack in the heat exchanger has a significant impact on the comfort and safety of your home so at Access Heating & Air Conditioning we make sure to go the extra mile for your benefit.

Warranty on a Cracked Heat Exchanger

Most furnaces that are 20 years or newer have warranties that cover the part replacement for the cracked heat exchanger. However, the availability of the part and the cost of labor is what often drive Boise homeowners to replace their furnaces instead of fixing the part. It is worth the time to explore both options before moving forward. Newer furnaces, like Trane, have 99-year warranties on their heat exchangers.

Why an Entire Blog Post About Cracked Heat Exchangers?

There are many companies, as we are finding more and more these days, that just want to scare homeowners into buying a new furnace while under pressure during the coldest part of the winter. It is certainly difficult to make a level-headed decision when your home is freezing!

Every winter we run second opinion calls and find that the heat exchanger isn’t cracked. And sometimes we find the right cracks and fractures where another company just marked the heat exchanger cells with a pencil to make it look like it was cracked! We take this service and diagnostic procedure very seriously because the safety of our homeowners relies on our expertise.

We are one of a very select and few companies in all of Idaho that have licensed heat-exchanger experts. If another company is telling you to buy a new furnace, we can provide a free second opinion over the phone. If you feel like a visit is necessary, we can perform that service for you as well. Our licensed service technicians can go through your system from top to bottom and make sure that your furnace is operating safely and properly.

Call us today to service your furnace and heat exchanger! An ounce of prevention is worth a pound of cure!


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