Signs Your Furnace Heat Exchanger Has Gone Bad

A gas furnace’s heat exchanger is mainly responsible for heating the air so that it is safe and warm as it circulates through the ducts and vents to the rooms in your home.

If problems occur with the heat exchanger, it can affect the entire heating system and present serious health risks to the family due to carbon monoxide leaks. If serious furnace problems occur in midwinter, Calgarians are in for a big shock as the temperatures plummet and the heating system needs fixing.

So, understanding the signs of a bad heat exchanger and what to do if problems occur is an important part of troubleshooting a malfunctioning furnace. Let’s find out more.

The heat exchanger in gas furnaces is usually a large metal box with metal tubes running through it. This component is considered central to the furnace, heating the air and helping to maintain the safety of the combustion process.

To create heat, a gas furnace combusts gas in a sealed chamber. The gases produced stream into the heat exchanger, heating the tubes. Toxic “flue gases”, such as carbon monoxide, are shielded from entering the blower, which helps to transfer heat from the exchanger’s hot surface to the atmosphere. The warm air is distributed through the home’s ductwork while the toxic flue gases are channelled to the chimney flue and vent outside the home.

For this to be a safe and effective process, the heat exchanger must have an air-tight seal and remain free from damage. This will prevent unhealthy gases from escaping and contaminating the air you breathe in your home.

In high-efficiency or “condensing” furnaces (over 90 percent efficiency), there are usually two heat exchangers while older, more traditional furnaces (70-80 percent efficiency) feature just a single heat exchanger.

Most furnaces sold in Alberta nowadays are considered high-efficiency and have two heat exchangers.

The primary heat exchanger is usually made of aluminized steel and is positioned close to the burners. The combustion gasses encounter this component first.

The secondary heat exchanger in high-efficiency furnaces extracts additional heat by changing water vapor to a liquid, generating heat for the home that would otherwise be expelled through the chimney flue and lost. This component is usually made from stainless steel or a coated steel material that can withstand moisture and acid.

Because of the greater stresses (heat and gas exposure) placed on the primary heat exchanger, it is usually more likely to crack and become damaged.

Heat exchangers go bad and fail for several reasons. They are exposed to high heat and a variety of gases that can cause problems.

Standard wear and tear accounts for many issues. Because heat exchangers are made of metal, they continually expand and contract as the furnace powers up and powers down. After 15-20 years of doing this, it’s quite natural for problems to arise.

If regular furnace maintenance is neglected, damage is likely to occur earlier than this. It’s important, therefore, for a professional to inspect and service your furnace at least once a year before the winter.

Typical issues include a dirty, clogged air filter that restricts airflow through the furnace causing the heat exchanger to overheat and leading to stress cracks over time. Another reason for a failed heat exchanger is a furnace that is poorly sized for the home, especially an oversized furnace, which can cause dangerous cracks to appear.

A crack in one of the cells of the heat exchanger could mean that toxic gases, including carbon monoxide (CO), sulfur dioxide (SO2), and nitrous oxide (N2O or laughing gas) may leak into your home and pose a risk to your family. CO is a colorless, odorless gas that is particularly difficult to detect without specialist equipment.

It helps to know the common signs of a cracked heat exchanger so that you can then take evasive action and prevent dangers by calling a professional plumber or HVAC technician, The main signs are:

• Unpleasant or strange odors (especially the smell of formaldehyde)
• White soot buildup in or around the furnace’s burners
• Visible corrosion or cracks in other furnace components, such as the draft diverter box or inducer motor
• A change in the color of the gas flame from blue to orange or yellow (which may indicate the presence of carbon monoxide)
• A rattling, popping or banging noise as your thermostat turns on the heat, caused by the expansion of the cracked metal
• An alarm from a carbon monoxide detector alerting you of the presence of CO

A furnace will usually run with a cracked heat exchanger, continuing to heat your home. If your furnace stops working completely, it’s likely due to something else.

However, it’s still essential to understand and identify the main signs of a cracked heat exchanger because it can be a “silent enemy”, causing you and your family harm even while everything appears to be fine.

Ultimately, a cracked heat exchanger is not safe and needs attention or you will be risking your health. Exposure to carbon monoxide can even be fatal.

Preventing such worries with an annual inspection and tune-up of your furnace is the best way forward for Calgary homeowners.

If you’re in Calgary, our licensed professional plumbers can help you resolve all common winter plumbing problems. Call Pete the Plumber at (403) 257-1766 to arrange a visit.