How dangerous is a crack in my heat exchanger?

How dangerous is a crack in my heat exchanger?

Had an HVAC technician out to service your equipment? Did they find a crack in the heat exchanger? Did they tell you that you needed a new furnace? What’s the big deal? Are you in any danger?

First of all, before you do anything else…

Ask your technician to show you the crack(s). There are companies out there that use this tactic to scare customers into making a rush decision to purchase new equipment.

Reputable companies will have sent their technicians to seminars or classes on how to identify hazardous cracks in heat exchangers. Always ask your technician if he/she is certified to identify cracked heat exchangers.

Why do all furnaces eventually develop these cracks?

Any furnace from any brand made by any company will eventually develop a crack in the heat exchanger… It’s just a property of these furnaces! The heat exchanger is meant to hold the combustion from your fuel source in-line with the air that flows through your home. As the combustion happens, the metal of the exchanger expands until it cools off again and contracts. All of the expanding and contracting stresses the metal and eventually leads to failure.

What do these cracks look like?


These cracks above are very serious and also very obvious. They were from a furnace that was not too old and they were located near the burners at the hottest part of the exchanger.

What is the danger?

Cracks in the heat exchanger are no laughing matter. There are two major dangers with these cracks: The first is the potential for the furnace to catch fire and potentially spread to other parts in the home. The second danger is carbon monoxide emissions.

Flame-outs and Furnace fires

Flame-outs occur when an incorrect mixture of gas and air get mixed and combusted in the heat exchanger. Uncombusted gas builds up in the exchanger until it reaches a high enough volume to be explosive. When that point is reached, the gas combusts and forces flames and air pressure out of any accessible hole in the heat exchanger… including the cracks.
Maintaining proper fuel to air mixtures is a routine item to check in most annual maintenances.
Furnace fires are fairly common. According to FEMA, they occur about 1,800 times per year. Damage associated from furnace fires varies with the severity of the surrounding structure however it is estimated that the average loss for furnace fires is roughly $5,027.

Carbon Monoxide leaks

Carbon Monoxide poisoning can be a scary thing. It can also be a scare tactic used to entice you to purchase a new furnace. But how bad is it really?
For Carbon Monoxide to leak into your living space from your furnace, the proper variables must be in line…

  1. There must be an improper mixture of air and gas to produce Carbon Monoxide.
  2. There must be a crack or leak from the heat exchanger into the home air flow.
  3. The inducer motor that pulls air through the heat exchanger must be not functioning properly.

Any 2 of the 3 variables will not result in Carbon Monoxide emissions into the living space from your furnace. However, it may not take much for your furnace to have all 3 variables.

If you feel that you’ve been “had” by another company, give us a call! We offer a free Second Opinion to give you peace of mind when it comes to your furnace safety.