The heat exchanger plays a pivotal role in how your home's furnace operates. In essence, it's designed to harvest the heat found within the furnace's combustion gases and transfer it to indoor air without allowing the gases and indoor air to mingle with one another.
If the heat exchanger fails, you won't be able to operate your furnace safely. By understanding the warning signs of a failing heat exchanger, you can have it repaired before your furnace becomes unsafe to operate.
Common Reasons for Heat Exchanger Failure
Heat exchangers are typically designed to last for the life of the actual furnace. However, it's not out of the ordinary for a heat exchanger to experience some degree of metal fatigue. This usually occurs due to the constant stresses placed on it by frequent heating and cooling of the metal structure.
In some cases, this can cause cracks to form near and around the weakest areas of the heat exchanger. These areas tend to be the spot welds on the heat exchanger and places where the metal bends or thins out for structural or packaging reasons. Overheating issues caused by poor or deliberately blocked airflow can easily accelerate metal fatigue issues.
Another common reason for heat exchanger failure involves rust and corrosion. A modern condensing furnace also extracts moisture out of the air as a byproduct of the heat it also extracts. This condensation usually contains corrosive elements that could easily eat away at the surrounding metal. Rust and corrosion can leave behind microscopic holes that allow poisonous carbon monoxide gases to seep through.
How to Spot the Warning Signs
One of the many signs of a heat exchanger that's in need of expert attention is a condition known as flame rollout. This happens when an excess of combustion byproducts in the heat exchanger crowds out the available oxygen for the burner. The burner flame eventually rises above the burner in search of more oxygen, creating a flame rollout.
Keep in mind that this is just one of several warning signs when dealing with heat exchanger problems:
- CO detector alarms – If poisonous CO gases escape from the heat exchanger, your CO detector will likely detect the amount of CO gases currently present in the air and alarm you once current levels exceed recommended safe levels.
- Sudden heat loss – A sudden lack of heat can also be a warning sign of a failing heat exchanger, especially if an inspection of the burner and gas supply turns up empty.
- Visual damage – In a few rare cases, you may even be able to see a visible crack or signs of rust and corrosion on the heat exchanger itself. However, it's usually difficult to conduct a visual inspection without opening up the furnace.
Getting Your HVAC Technician Involved
When it comes to inspecting your heat exchanger, your HVAC technician can do a much more thorough job of tracking down and identifying potential problems. In fact, your HVAC technician may use one or more of the following techniques to inspect and verify heat exchanger issues:
- Pressure testing – All of the heat exchanger's openings are sealed up while the furnace fan operates. Using a pressure gauge, your HVAC technician can tell if there's any air leakage.
- Smoke bombs – Your HVAC technician places a small smoke bomb in the heat exchanger. Cracks and gaps are identified by smoke leaving these openings.
- Tracer gases – Instead of smoke bombs, your HVAC technician will use methane tracer gas to detect leaks.
- Salt solution – Your HVAC technician sprays a salt water mix into the combustion chamber and a small torch somewhere within the supply ducting. A leak in the heat exchanger will cause the flame to turn a different color.
If there are any problems with your heat exchanger, your HVAC technician may suggest to either repair the problem or purchase and install a new heat exchanger. However, the time and expense required for such a job often makes buying and installing a brand-new furnace a more cost-effective and relatively hassle-free solution.
Knowing how to identify potential heat exchanger problems is essential for proactive furnace maintenance. For more information on what you can do if you suspect a problem with your heat exchanger, contact a heating and air conditioning repair company in your area.