At the heart of every modern high-efficiency furnace lies the heat exchanger. As your furnace produces combustion gases by burning its fuel, the heat exchanger essentially scavenges the heat found within the combustion gases as they travel through the exchanger's various tubes or coils. The heat is then transferred to the passing air so it can be circulated throughout your home.
A failing heat exchanger represents a serious health and safety risk to you and other occupants in your home. Knowing the signs of heat exchanger failure along with what to do in the event of a failure can help you protect your home against this type of furnace breakdown.
Why Heat Exchangers Fail
Most heat exchangers fail due to metal fatigue. The constant heating and cooling experienced by a heat exchanger throughout its working life can cause the metal to weaken over time. This can result in stress cracks forming in areas where the metal is at its weakest (usually around welds, seams, and bends in the heat exchanger pipe or coil). Although these cracks are usually microscopic in nature, some cracks can grow large enough to allow carbon monoxide and other combustion gases to escape.
Rust and corrosion can also play a significant role in heat exchanger failure, especially in high-efficiency condensing furnaces that produce large amounts of corrosive condensate. As rust eats away at the heat exchanger, it can leave behind microscopic holes that allow poisonous combustion gases to escape.
Furnace overheating and short cycling can easily hasten a heat exchanger's demise. A clogged furnace filter or blockages elsewhere in the furnace ductwork can cause the heat exchanger to overheat and create new stress cracks (or worsen existing cracks). Short cycling prevents the furnace from running long enough to evaporate corrosive condensate, setting the stage for severe rust. Improper drainage can also lead to rust and corrosion formation.
Warning Signs to Watch Out for
If you're worried that your furnace may be experiencing heat exchanger failure, you may want to look for these signs:
- Your furnace fails to produce heat despite troubleshooting all other possible causes of a no-heat condition (including thermostat failure and faulty relay switches).
- Your carbon monoxide (CO) detector senses dangerous amounts of CO gas in your home's indoor air.
- Your furnace constantly experiences flame rollout, where the burner flame grows in search of oxygen due to the heavy presence of combustion gases.
- You can actually see signs of rust and corrosion or visible cracks in the heat exchanger.
If you see any of these warning signs in your furnace, then it may be time to take a closer look at your heat exchanger.
Dealing with Heat Exchanger Failure
Dealing with a heat exchanger failure isn't for the faint-hearted. In fact, it's a task that's better left up to the professionals. Your HVAC contractor will be in a better position to diagnose heat exchanger issues and make the appropriate repairs or replacement.
Your HVAC contractor may use a variety of diagnostic tools and techniques to verify heat exchanger failure. These techniques include the use of smoke generators, methane tracer gas, and saltwater solution to locate leaks within the heat exchanger. The most common diagnostic technique involves pressure testing, where every opening in the heat exchanger is sealed and pressures within the component are measured with a pressure gauge.
Replacing a heat exchanger is often a time-consuming and expensive task, with most contractors charging between $600 and $1200 for a typical replacement job. The work is often so extensive that many HVAC contractors will suggest you have the entire furnace replaced instead. If your current furnace is over 10 years old, it may be worth your while to have it completely replaced in the aftermath of a heat exchanger failure.
For more information and assistance with diagnosis and dealing with heat exchanger failure, contact HVAC contracting companies like Dick Kearsley Service Center.