Keeping Your Home Cool during the Sweltering, Summer Months

How To Spot Heat Exchanger Problems With Your Gas-Powered Furnace

by Anthony Graves

The heat exchanger plays a critical role in the operation of your gas-powered furnace. Unfortunately, it can also be your furnace's Achilles heel, especially if your furnace hasn't been maintained properly. The following explains some of the issues you can run into when it comes to your heat exchanger. You'll also learn how to spot heat exchanger problems and what you can do to have these issues cleared up promptly.

Common Heat Exchanger Issues

Metal fatigue is one of the most common types of heat exchanger failure. The frequent thermally driven expansion and contraction of the heat exchanger's metal surface can provoke microscopic stress cracks throughout the component. Over time, these cracks can grow large enough to allow combustion gases to escape the heat exchanger. Although metal fatigue is usually an issue faced by heat exchangers in older furnaces, it can occur prematurely if the furnace overheats due to short cycling or ductwork blockages.

Severe rust and corrosion can also lead to heat exchanger failure. It's a common problem in high-efficiency condensing furnaces, since these units produce corrosive condensate as a byproduct of the combustion process. Rust and corrosion can eat away at the thin metal surface of the heat exchanger, leaving behind microscopic holes and other weak areas where combustion gases can escape.

Warning Signs

Here are a few warning signs to look out for when it comes to heat exchanger failure:

  • No-heat condition - A lack of heat is often the first sign of heat exchanger failure, although it's a good idea to rule out other potential causes.
  • Flame rollout - A heat exchanger failure resulting in excess soot buildup and oxygen starvation can cause the burner flame to grow beyond the burner opening and roll out of the heat exchanger.
  • Unsafe CO levels - Heat exchanger leaks can also cause odorless, colorless carbon monoxide (CO) gases to leak into your home; if your CO detector constantly goes off, you may want to have a professional check your heating system for combustion gas leaks.
  • Visible rust or damage - In some cases, the toll taken on your heat exchanger can actually be seen from outside your furnace; if you can actually see rust, corrosion, or cracks in the heat exchanger, then you should shut off your furnace immediately and call your technician as soon as possible.

Diagnosing Heat Exchanger Issues

For starters, your HVAC technician may decide to perform pressure testing on your furnace's heat exchanger. This usually involves sealing all of the heat exchanger's openings and watching for any changes in air pressure while the blower fan is in operation. Tracer gases and smoke generators may also be used to detect cracks and other unexpected openings in the heat exchanger.

Another common testing method involves the use of a saltwater solution, which is sprayed into the combustion chamber during operation. A small torch is placed further along the supply air ductwork. If there are any leaks in the heat exchanger, the saltwater vapor will cause the torch flame to momentarily change color.

Should You Repair or Replace?

In some cases, it may be possible for your HVAC technician to make minor repairs to your heat exchanger. For more serious issues, however, your technician will usually recommend a complete replacement of the heat exchanger. Unfortunately, the cost of replacing a heat exchanger can easily approach that of purchasing and installing a brand-new furnace. If your furnace is more than 10 years old and needs a heat exchanger replacement, you are usually better off replacing the entire furnace instead.

For more information, contact an HVAC company like Custom Comfort.