Is There a Crack in Your Furnace Heat Exchanger?

Now is the time of year to have your home or building furnace professionally checked for safety and efficiency.  If you wait until your system has a problem or the first cold weather to arrive, you’ll have to compete for service with everyone else who waited until the last minute. Then, it may cost more, and you’ll have to wait longer for service.

While monitoring an HVAC industry forum recently, I read a flurry of posts and some controversy about cracks in heat exchangers.  For those who need background for today’s topic, the heat exchanger is a major part of the combustion area of a furnace.  It is also an expensive component to replace, and can create the need to have a new heating system installed.

When fuel is burned in a furnace, the exhaust gas must goes outside the house through a vent pipe and the desired heat (minus the vented gas) must be moved (usually by ducts) from the furnace to the part of the house or building that needs to be heated.  The gas to be vented outside and the desired warmth for the inside of the building must be kept apart. However, heat exchangers can develop cracks or holes due to age, rust, deterioration, flaws in the metal, etc. Since toxic carbon monoxide gas is present (in varying amounts) during fuel combustion, this topic can literally be one of life or death.

In the forum I was reading, two schools of thought from HVAC contractors, inspectors and others on the topic are as follows:

a- If there is any kind of crack or hole in it, the heat exchanger must be replaced immediately. Their reasoning: anytime there is a crack, the combustion gas (and carbon monoxide) will (or has the potential to before the next inspection) enter the living areas. To this group, the potential injury or death is not worth any delay. They may even “tag” your heating system so it cannot be turned on until it is fixed.

b– If there is carbon monoxide detected in the system (the exact way it is measured can vary per the HVAC code in your state or local area), the heat exchanger must be replaced. They focus on being able to measure carbon monoxide at a specific point or level rather than focusing on the underlying (or potential) underlying cause. This group seems to be concerned about potential “overzealous” replacement of the heat exchangers, and that the expense involved might be an unnecessary one.

Consider Asking For A Second Opinion

I happen to be strongly on the side of group a, the cautious group.  Personally, having lived through a few accidents and serious illnesses,  my first goal above everything else is to stay alive and healthy.  I’m going to take action to minimize/prevent this risk. I also use a home carbon monoxide alarm as additional backup protection.  For those who have a different opinion, though, there are some steps you could take to help you make a sound decision. For example, if you get the sense that a recommended replacement of your heat exchanger is only or primarily for the financial gain of the installer or you are concerned about the cost,  you can call another trusted local heating A/C service company for a second opinion. For a major repair or heating system replacement that involves a heat exchanger, second opinions are often free of charge.

If you have central air conditioning and heating, your furnace may outlive the AC equipment by a few years. However, if you have to replace the furnace due to a cracked heat exchanger, you may want to replace the whole heating/AC system.  You can read reasons why on our page about system repair and replacement.

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