What Is A Cracked Heat Exchanger?

What Is A Cracked Heat Exchanger?

One of the biggest issues we find with older worn out furnaces in the Sioux Falls area is a rusted out or cracked heat exchanger. Many times there are cracks or rusted out spots that the client doesn’t even know about and are completely unrelated to the reason why they called for service. We only find these heat exchanger cracks by using a highly advanced heat exchanger inspection camera.

As a homeowner, getting the news that your heat exchanger is cracked can be a tough pill to swallow. Some clients try to ignore the issue and live in denial of the seriousness of a cracked heat exchanger since it is often unrelated to why we were called out.  Since the furnace is still operating as though there were no problem they don’t think they have to do anything to solve the issue.  The reality of a cracked heat exchanger means that the furnace needs to be condemned until their the heat exchanger is replaced or a new furnace is installed. Failure to take action means potentially putting your life as well as the life of your family in jeopardy.

cracked water heat exchanger

A Cracked Clamshell Style Heat Exchanger

Don’t get me wrong, I don’t want you to think that every crack in a heat exchanger is going to result in death or violent illness due to carbon monoxide poisoning. However, according to the American Gas Association:

“Any visible crack or hole is reason for requiring replacement of the heat exchanger or furnace.”
-American Gas Association

What does the heat exchanger do?

At it’s most fundamental level, a heat exchanger allows for the exchange of heat between two air streams without the air mixing. The return air from the home and the hot exhaust from the combustion of gas are seperated by sheet metal and tubing that typically snakes back and forth to allow for the maximum amount of air to pass over it and the most heat to be exchanged between the two streams. As the furnace’s blower motor blows the return air through the heat exchanger the air becomes warm and the heat exchanger is cooled before the inducer motor pulls the exhaust gas out of the furnace and vents it outside of the home.

Tube Style Heat Exchanger

Tubular Style Heat Exchanger

Inside of your furnace or boiler there is actually a fire burning.  Natural gas or propane is being burned and the byproduct of that process is energy in the form of heat, along with water vapor (H2O), carbon dioxide (CO2), carbon monoxide (CO), carbon (or soot; C) and Nitrogen Oxides (NOx). With the exception of some additional water vapor in the home during the winter months for humidification, CO2, CO, soot, and NOx are pollutants and all of them can cause sickness or be fatal in high enough quantities.

Why Do Heat Exchangers Crack?

Heat exchangers are not designed to crack early or often. They are designed to provide safe operation of the furnace during its life expectancy, which is typically about 12-15 years.  However, there are many factors which can accelerate the wear and tear on a furnace’s heat exchanger which will cause them to fail much sooner.

Sometimes heat exchangers fail from age and normal usage.  In Sioux Falls it is not uncommon for furnaces to see over 1,000 hours of use each winter.  If we assume the average heating cycle is 15 minutes long, then that heat exchanger is heating up and cooling down about 4,000 times per year. Sometimes it takes 10 years and sometimes it takes 20 years before the heat exchanger cracks. Then again, sometimes they never crack and they are replaced simply because of other expensive repairs or the efficiency gain is enough to warrant replacment of the furnace.

More commonly, the cause of a cracked heat exchanger is misapplication or poor maintenance of the furnace.  All too often, furnaces are massively oversized or used incorrectly which causes the heat exchanger to fail prematurely. When a furnace is oversized, a number of problems can exist including short cycling and cycling on limit.  Both of these cause the heat exchanger to heat up and cool down far more often than if the furnace was closer to the proper size for the home or, better yet, was able to use a lower stage or modulate its heat output for smaller loads.

Another reason for heat exchanger failure is lack of airflow.  The primary cause of low airflow in your furnace is a dirty filter. If your filter gets clogged with dust and dirt and the air simply can’t get through, your furnace will overheat and die.  The heat simply won’t be able to get out and the furnace will likely cycle on its high limit until it ceases to function or you change the filter.  Poor airflow can also be the result of a plugged indoor coil, poor ductwork design or installation or simply not having enough ductwork to support the size of the furnace.  Meanwhile, your heat exchanger will go through a lot of stress when it is constantly overheated and cooled back down.

Sometimes it can be relatively easy to see cracks in a heat exchanger. However, what about when the cracks are just beginning or what if it doesn’t seem to be in a serious area?  At Comfort Heroess, LLC we concur with the American Gas Association and AHRI that any crack, hole or other failure of the heat exchanger is reason to replace the heat exchanger or the furnace itself.

What we do when we find a cracked heat exchanger?

If while we are inspecting your furnace we discover a crack, rusted out section or evidence of any other failure in the heat exchanger we will immediately condemn the furnace and get options together for you to either replace the heat exchanger (if it is still available) or replace the furnace. When it comes to the risk of carbon monoxide poisoning there is no safe limit for you or your family.

If you would like to have your furnace inspected and cleaned it’s not too late in the season. Call our team of licensed professional furnace mechanics and we will get your systems checked out for you!

Comfort Heroess, LLC serves homeowners in Sioux Falls, SD and the surrounding areas.