How could a little crack be a problem?
Service technicians / contractors who turn a furnace back on because the crack in the heat exchanger is not serious are not doing the homeowner a favor in the long run. In fact that contractor is not following American Gas Association guidelines. The crack itself is only a sign of troubles to come. The cause of the crack needs to be established, and repairs have to be made, or the crack along with the associated danger will grow larger. Heat exchangers with cracks do not heal themselves; cracked heat exchangers need to be replaced. The cavalier act of turning a furnace with a cracked heat exchanger back on without making repairs is in fact putting the technician, the contractor, and the homeowner at risk. Heat exchangers are, simply, fire containment boxes that are inside of the duct system. They keep the fuel and fire on one side (venting through to the outside) and the supply air for heating on the other. Blower fans in most furnaces wait for the heat exchanger to warm up before they
