Understanding the Problem of a Heater with a Cracked Heat Exchanger

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If you are preparing for the heating season by scheduling your annual furnace inspection, then you may be surprised when your HVAC person tells you that the heat exchanger has a crack in it. This is a serious situation, and your heating professional will likely tell you this. If you are confused about the problem, what it means, and how a fix will be completed, keep reading.

What Is the Heat Exchanger?

Inside your furnace, you will see a series of metal pipes or long tubes that run across the top of the heater. These tubes or coiled metal parts are the heat exchanger, and they will sit just above the combustion chamber of the furnace. The combustion chamber will burn gas, oil, or propane fuel to create heat. The warm air and the combustion gasses that are created in the chamber rise through the heat exchanger and up through the venting system of your home. The combustion gasses then release out through your chimney. As the heat exchanger heats up, a blower will force cool air over the exchanger. The air warms and then moves through your vents to heat your home. 

Heated gasses and air do not move through your home. The heat instead transfers from the metal coils to the cool air blowing past them. The heat exchanger and the combustion chamber are part of a closed system that is only open to the outdoor chimney and vent. 

What Are the Dangers of a Cracked Heat Exchanger?

Since heat exchangers are made out of metal, heat will cause them to expand. Many exchangers are made out of steel, and steel is a highly durable material. However, if steel is warmed or cooled too quickly, then steel can crack. This often happens if your furnace sits in an extremely cold basement or if the system is burning too hot for the heat exchanger to handle. 

Smaller cracks will often form in a heat exchanger at first. Over time, these cracks will widen and open up more and more. Even a small crack can allow some of the combustion gasses that run through the metal tubing to escape. These gasses include carbon monoxide, and the gasses will be forced up through your vents with the help of your furnace blower. This carbon monoxide is dangerous and can reduce the amount of oxygen that your body is able to hold in your blood. Unfortunately, carbon monoxide is colorless and odorless, so poisoning is extremely difficult to detect and is best avoided. 

How Is a Cracked Heat Exchanger Repaired?

If you have been informed that your furnace has a cracked heat exchanger, it is wise to stop using your heater as soon as possible. Even a small amount of carbon monoxide in your home is dangerous. Your heating specialist will need to attend to a repair of the heating system. There are several ways that the heat exchanger can be fixed. If the unit is a steel one, it may be able to be repaired with a welded patch over the crack. Your HVAC professional will typically need to complete a thorough inspection of the entire heat exchanger with a thermal camera first to make sure only one crack is present and needs fixing. If numerous cracks are present, then the exchanger unit may need to be replaced.

Some furnaces and heaters will have heat exchangers that are attached directly to the combustion chamber. This makes replacement difficult and expensive. A new heating-system installation may be suggested. While this may not be ideal, it is often the safest choice when a cracked heat exchanger is found and a repair is needed. To help offset costs, opt for the most efficient heating system that you can afford to replace your old one and talk to a contractor such as Hartman Heating, Air and Fireplaces to get started.