Diagnosing And Correcting Heat Exchanger Failures

The heat exchanger is one of the most important parts of your home's furnace. Consisting of a collection of chambers and passageways, it keeps your furnace's combustion gases separate from indoor air while allowing heat to pass from one medium to another. A heat exchanger failure can signal a quick end of your furnace's heating days unless it's properly diagnosed and repaired.

How Do Heat Exchangers Fail?

A heat exchanger in a typical furnace can last as long as the furnace itself - roughly around 15 to 25 years, under most circumstances. During that time, a heat exchanger can experience metal fatigue due to the constant heating and cooling it's subjected to. This metal fatigue can cause cracks to form around the welds and bends of the heat exchanger, exposing your home to carbon monoxide (CO) dangers.

Aside from old age, there are other ways that a heat exchanger can fail:

  • Restricted airflow caused by a clogged furnace filter or undersized ductwork can cause the heat exchanger to overheat, accelerating metal fatigue and causing the heat exchanger to develop stress cracks.
  • Short cycling can prevent condensate formed within the heat exchanger from evaporating, allowing it to foster rust and corrosion within the heat exchanger itself. Corrosion can create microscopic cracks and holes throughout the heat exchanger.

Cracks and holes in a heat exchanger not only allow poisonous CO gases to seep out of the furnace, they also allow air to seep within the heat exchanger itself. This often leads to airflow disruptions that cause flame rollout, rendering the furnace unable to warm your home.

How Can You Check for Failure?

In most cases, a heat exchanger failure often leads to a no-heat condition for your furnace. In others, a crack heat exchanger can actually set off your CO alarm if CO gases escape in large enough concentrations. You can attempt to pinpoint the crack or hole in question through a visual inspection of the heat exchanger itself. Although the vast majority of cracks are found this way, it can be surprisingly difficult to conduct a thorough visual inspection on a modern forced air furnace.

It's better to let your HVAC technician hunt down the source of your heat exchanger leaks, using the following inspection methods:

  • Smoke Bomb Test – Your HVAC technician places a smoke generator within the heat exchanger and looks for smoke escaping through holes and cracks.
  • Wintergreen Oil Test – Your HVAC technician turns on the blower fan and sprays oil of wintergreen or a similar odorant into the combustion chamber. If the smell of wintergreen oil permeates throughout the home, cracks within the heat exchanger may be present.
  • Pressure Testing – The technician seals all openings on the heat exchanger and turns on the blower fan. A pressure sensing gauge is connected to the heat exchanger's pressure sensing port. Gauge readings can indicate whether air from the blower fan is leaking into and pressuring the heat exchanger.
  • Tracer Gas Test – With all openings sealed, a methane tracer gas is fed into the heat exchanger. Your HVAC technician passes a leak detection device around the outside of the heat exchanger in search of escaping tracer gases.
  • Salt Test – Your HVAC technician sprays a salt solution into the combustion chamber and mounts a torch through a hole created in the supply ducting. If there's a leak in the heat exchanger, the salt solution will cause the torch flame to change color.

What to Do When It Fails?

A heat exchanger failure presents you with two solutions: you can have the heat exchanger repaired or you can have it replaced.

Heat exchanger repairs typically consist of welds or patches that either seal or cover up cracks and holes throughout the surface. While such repairs are doable, they're usually more trouble than they're worth. The patches can fail in short order due to excess heat and continuing rust and corrosion. Patches can also present a safety risk for anyone operating the furnace.

The better option involves a complete replacement of the heat exchanger, as well as a correction of any underlying problems that could contribute to heat exchanger failure. It's a safer option that also nets your furnace better performance and energy-efficiency throughout its remaining lifespan. Contact an HVAC company at a site like http://rbincorporated.com/ to have your heat exchanger replaced.


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