If you were told that you have a cracked heat exchanger from a service technician the chances are great that is why you are here today. He or she may have even told you that they have to “red tag” the furnace due to safety issues. Most furnaces if left in a home long enough and under the right circumstances will develop a crack in the heat exchanger or fire box. There is plenty of information on the Internet when it comes to learning about what a heat exchanger is and what it does. Some of them are good and some leave much more to be desired.  This site was built for homeowners to explain what a cracked heat exchanger is in a furnace, how it can happen and what can happen when it occurs. Included is what flame roll out is and how it occurs. This site was not built for technicians so the explanations are hopefully simple enough to understand. If you think that you have a crack in your heat exchanger find someone who is qualified to determine that for you it’s not worth guessing.