The Toxic Dangers of a Cracked Heat Exchanger

The heat exchanger is the part of your furnace that warms the air flowing through your heating system. It also has another critical function: it keeps your indoor (breathing) air separate from the toxic gases your furnace creates during combustion. A crack in this essential furnace component can compromise your indoor air quality.

How Does the Heat Exchanger Work?

When your furnace and its heat exchanger are working correctly, here’s what happens:

• Your furnace creates heat energy by combusting (burning) fuel like gas, oil, or propane.
• For safety reasons, this combustion happens in a sealed chamber. You don’t want flammable gas filling up your home. You also don’t want the poisonous flue gases created by the combustion process to enter your air supply.
• The heat energy created by combustion warms up your heat exchanger.
• At the same time, the blower “blows” cold air from your home over your heat exchanger, and this warms up the air.
• Your heat exchanger acts as a barrier between that air from your home and the poisonous flue gases so that the two won’t mix during the air-heating process. This ensures that you’ll have air that’s safe to breathe.

Unfortunately, many heat exchangers don’t last forever. The exchanger goes through frequent temperature changes, which causes the metal to expand and contract. Over time, this stresses the material, making it more prone to cracks. Other factors can cause this to happen prematurely, which we’ll discuss more below.

Why Is a Cracked Heat Exchanger Dangerous?

A cracked exchanger allows your furnace’s flue gases to mix with the “breathing air” inside your home. This could trigger many adverse health effects. When your heating system is sealed and functioning properly, those fumes are vented outdoors, where they can’t accumulate in harmful concentrations.

Just what comprises flue gases? The exact composition varies based on the type of fuel your furnace uses and how efficiently it’s using it, but typically, you can find these harmful substances in combustion gases:

• Nitrogen oxides
• Sulfur oxides
• Soot particulates

If your furnace simultaneously has a cracked heat exchanger and a combustion problem, toxic concentrations of carbon monoxide (“the silent killer”) might also infiltrate your home’s air supply. All of these substances are dangerous to breathe even in low concentrations, and they pose an especially high health risk to infants, children, the elderly, and those with lung or heart conditions.

What Causes a Cracked Heat Exchanger, and How Can You Avoid this Problem?

As mentioned above, sometimes a heat exchanger will crack simply due to old age. However, other factors can cause added stress to a heat exchanger beyond everyday expanding and contracting.

• Lack of airflow. When your heating system doesn’t have enough air flowing through it, the heat exchanger can overheat and form stress cracks. The easiest way to avoid this is by routinely replacing your air filter.
• An oversized furnace. When your furnace is too large for your home, it will run for extremely short cycles, putting the exchanger through frequent heat stress. Condensation also tends to collect in oversized furnaces, which can cause the exchanger to rust. When replacing your furnace, always opt for a professional installation to avoid sizing issues.

Can You Remember the Last Time Your Furnace Had a Safety Inspection?

During an annual HVAC maintenance appointment, your technician from Tom's Mechanical, Inc. will provide your heater with a professional tune-up and check for any potential safety issues, including a cracked heat exchanger. Schedule your appointment online or by giving us a call at (972) 388-3669.